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BPSK Modulation Using Operational Transconductance Amplifier

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Acknowledgement

I express my sincere gratitude to my mentor Prof. Baidyanath Ray for helping methroughout, with his valuable and worthwhile experience. He regularly gave me various ideas

and suggestions through which i learnt the subject in a practical approach. His encouraging

words constantly inspired me to be innovative in my approach and to cross the incoming hurdles

in an efficient manner. I also extend my thanks to the department for providing me with the

technical facilities as and when required.

I am also highly obliged to the Officer-In-charge ofDefence Research and Develoment

Organization, Advanced Technology Cell, Jadavpur University for accepting my project

concept. They granted Rs.7,000/- as economical help for our project purpose and Rs.3,000/- as

scholarship.

SIGNATURE OF STUDENT


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Contents Page No

LIST OF FIGURES 4

1. ABSTRACT 7

2. MODULATION 9

2.1 Overview 9

2.2 Purpose of Modulation 10

2.3 Digital Modulation 10

2.4 Fundamental Digital Modulation Methods 10

3. BINARY PHASE SHIFT KEYING 12

3.1 Introduction 12

3.2 Modulation Technique 12

3.3 Demodulation Technique 14

4. OSCILLATOR 15

4.1 Overview of Oscillator 15

4.2 Principle of Operation 15

4.3 Stability of Oscillator 16

4.4 Types of Oscillators 17

5.VOLTAGE CONTROLLED OSCILLATOR 205.1 Overview 20

5.2 Types of VCOs 20

5.3 VCO time-domain equations 21

5.4 VCO frequency-domain equations 21

5.5 VCO Parameters 22

5.6 VCO Applications 22


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Contents Page No

6.PHASE SHIFTER 23

6.1 Overview 23

6.2 Classification 23

7.CURRENT MODE DEVICE 25

7.1 Introduction 25

7.2 Current Conveyor 25

7.3 Switched Capacitor 28

7.4 Differential Pair Transconductor 29

7.5 Cross-Coupled Differential Pair 31

7.6 Operational Transconductance Amplifier 32

7.7 Reasons For Choosing OTA as Main Building Block 36

7.8 Model Parameter Of MOS Used For Simulation 36

8.BLOCK DIAGRAMS 37

8.1 Voltage Controlled Oscillator 37

8.2 Phase Shifter 37

8.3 BPSK Modulator 38

9.SIMULATED OUTPUT 39

9.1 Lineariaty Check 39

9.2 Voltage Controlled Oscillator 40

9.3 Phase Shifter 41

9.4 BPSK Modulator 42


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Contents Page No

10. SPREAD SPECTRUM MODULATION 44

10.1 DESIGN OF LFSR 44

10.2 DESIGN OF FCSR 45

10.3 DESIGN OF MODULATOR 45

11. PROGRAM & OUTPUT 46

11.1 LFSR PROGRAM 46

11.2 LFSR PROGRAM OUTPUT 46

11.3 FCSR PROGRAM 47

11.4 FCSR PROGRAM OUTPUT 49

11.5 COSINE PROGRAM 50

11.6 MODULATION PROGRAM 50

11.7 MODULATION PROGRAM OUTPUT 51

12.APPLICATIONS IN DEFENCE 5313.FUTURE PROSPECTS 44

14.REFERENCES 45


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LIST OF FIGURES

Figure Page No

3.1 Block diagram of BPSK modulator 12

3.2 waveform of BPSK modulation 13

3.3 BPSK constellation diagram 14

3.4 Block diagram of BPSK demodulator 14

4.1 Block diagram of a positive feedback network 15

4.2 Bode Plot of an Unstable System 16

4.3 Pole Location of Stable & Unstable System 17

5.1 VCO Response Curve 20

7.1 Black box representation of the current conveyor 25

7.2 Nullator-norator representation of CCI 26

7.3 First-order CMOS implementation of CCI 27

7.4 Nullator-norator representation of CCII 28

7.5 Switched capacitor non-inverting integrator 29

7.6 Differential pair transconductor 30

7.7 Cross-coupled differential pairs 31

7.8 (a) Schematic of OTA (b) Equivalent circuit of OTA 32

7.9 Structure of proposed OTA 33

7.10 High frequency half equivalent circuit model of OTA 34

7.11 Simplified circuit model of OTA 35

8.1Block Diagram of VCO using OTA 37

8.2Block Diagram of PhaseShifter using OTA 37

8.3 Block Diagram of BPSK Modulator using OTA 38


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Figure Page No

9.1 Waveform for Linearity Check 39

9.2 Waveform for VCO 40

9.3 Waveform for Phase Shifter 41

9.4 Waveform for BPSK Modulation Bit 1 42

9.5 Waveform for BPSK Modulation Bit 0 43

10.1 Block Diagram of Linear Feedback Shift Register 44

10.2 Block Diagram of Feedback Carry Shift Register 45


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Abstract

In a communication system message signals are transferred between two entities via a

communication channel. However, depending on the channel and signal frequency domain

characteristics, the message signals produced by various information sources are not alwayssuitable for direct transmission over a given channel. When signal and channel frequency bands

do not match exactly, channels can not be moved. Hence, messages must be moved to the right

channel frequency bandwidth. Message signals must therefore be further modified to facilitate

transmission. In this conversion process known as modulation, the baseband signal is used to

modify one or more parameters of a radio-frequency(RF) carrier signal.

There are two types of modulation techniques:-

I. Analog Modulation.

II.

Digital Modulation.

In analog modulation, the message transmitted through the channel is analog in nature.

Whereas in digital modulation the message transmitted through the channel is digital. Because of

the various advantages of digital communication digital modulation is widely used.

Now, any signal can be characterized by three parameters: amplitude, phase & frequency.

Thus, by changing one or more of these three parameters of the carrier signal different

modulation schemes can be observed. Different digital modulation schemes are as follows:

Binary Amplitude Shift Keying(BASK)

Binary Phase Shift Keying(BPSK) Binary Frequency Shift Keying(BFSK)

Quadrature Amplitude Shift Keying(QASK)

Quadrature Phase Shift Keying(QPSK)

Quadrature Frequency Shift Keying(QFSK)

Quadrature Amplitude Modulation(QAM)

M-ary Amplitude Shift Keying(MASK)

M-ary Phase Shift Keying(MPSK)

M-ary Frequency Shift Keying(MFSK) etc.

In BPSK modulation technique, our topic of discussion, two different phases of the

carrier signal is used to modulate the two bits 1 and 0.

To generate the carrier signal an oscillator is required . An oscillator is an electronic

device that generates a repetitive electronic signal by using positive feedback. The main factor of


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any oscillator is its stability. For the purpose of modulation different carrier signals with different

frequencies are required. If different oscillators are to be used for each of the carrier then the cost

of communication will increase sufficiently. To overcome this situation voltage controlled

oscillator is used so that one voltage source can be used to tune to different frequencies.

Analog design has historically been viewed as a voltage dominated form of signal

processing. This has been apparent in analog IC design where generally current signals are

readily transferred into the voltage domain before any analog signal processing takes place. A

key performance feature of current mode processing is inherent wide bandwidth capability.

Recent advances in integrated circuit technologies have meant that the analog IC design is now

able to exploit the potential of current mode analog signal processing, providing attractive and

elegant solutions for many circuit and system problems.

The basic building block in this project is an operational transconductance

amplifier(OTA) which is a current mode device. It is basically a cross-coupled differential

amplifier with an output current that depends on the difference in voltage at the inputs. The

reason for choosing OTA as the building block is its high bandwith, large transconductance and

good linearity property. OTA is advantageous over other current mode device like JFET,

MOSFET in the sense that OTA has the much higher capability of withstanding the noise &

atmospheric attenuation.

It has linear transconductance charactaristics with respect to the amplifier bias current,

this can be considered as a gain controlled block

It has a good power supply rejection & common mode rejection than any differential

amplifier, above other mentioned

This is the cause of choosing this device as a basic building block of our modulator.

Frequency hopping is the most popular method of transmitting/receiving radio signals by

periodically switching carrier frequencies. It is realized by using pseudo-random sequencesgenerated by hopping algorithms. As carrier frequency changes continually, it provides an

effective firewall against the adversarys ability to follow the changes in carrier frequency. Thus,the adversary encounters difficulty to recover the data or information being carried. In addition,

the frequency hopping provides an effective tool for protection against frequency jamming byadversaries.

The switching of carrier frequencies is done with the help of FCSR (Feedback Carry Shift

Register), which produces pseudo-random sequence. The basic building block of any FCSR is an

LFSR (Linear Feedback Shift Register).


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MODULATION

2.1 Overview

In electronics and telecommunications, modulation is the process of varying one or more

properties of a high-frequency periodic waveform, called thecarrier signal, with a modulating

signal which typically contains information to be transmitted. Any of these properties can be

modified in accordance with a low frequency signal to obtain the modulated signal. Typically a

high-frequency sinusoid waveform is used as carrier signal, but a square wave pulse train may

also be used.

In telecommunications, modulation is the process of conveying a message signal, for

example a digital bit stream or an analog audio signal, inside another signal that can be

physically transmitted. Modulation of a sine waveform is used to transform a baseband message

signal into a passband signal, for example low-frequency audio signal into a radio-frequency

signal (RF signal). In radio communications, cable TV systems or the public switched telephone

networkfor instance, electrical signals can only be transferred over a limited passband frequency

spectrum, with specific (non-zero) lower and upper cutoff frequencies. Modulating a sine-wave

carrier makes it possible to keep the frequency content of the transferred signal as close as

possible to the centre frequency (typically the carrier frequency) of the passband.

A device that performs modulation is known as a modulator and a device that performs

the inverse operation of modulation is known as a demodulator (sometimes detectoror demod).

A device that can do both operations is a modem (from "modulatordemodulator").

If we look at a general function for a sinusoid:

we can see that this sinusoid has 3 parameters that can be altered, to affect the shape of the

graph. The first term, A, is called the magnitude, or amplitude of the sinusoid. The next term,

is known as the frequency, and the last term, is known as the phase angle. All 3 parameters can

be altered to transmit data.

The sinusoidal signal that is used in the modulation is known as the carrier signal, or

simply "the carrier". The signal that is used in modulating the carrier signal(or sinusoidal signal)

is known as the "data signal" or the "message signal". It is important to notice that a simple

sinusoidal carrier contains no information of its own.
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In other words we can say that modulation is used because the some data signals are not

always suitable for direct transmission, but the modulated signal may be more suitable.

2.2 Purpose of Modulation

The aim of digital modulation is to transfer a digital bit stream over an

analog bandpass channel, for example over the public switched telephone network(wherea bandpass filter limits the frequency range to between 300 and 3400 Hz), or over a limited

radio frequency band.

The aim of analog modulation is to transfer an analog baseband (or lowpass) signal, for

example an audio signal or TV signal, over an analog bandpass channel at a differentfrequency, for example over a limited radio frequency band or a cable TV network channel.

Analog and digital modulation facilitate frequency division multiplexing (FDM),

where several low pass information signals are transferred simultaneously over the sameshared physical medium, using separate passband channels (several different carrier

frequencies).The aim of digital baseband modulation methods, also known as line coding, is to

transfer a digital bit stream over a baseband channel, typically a non-filtered copper wiresuch as a serial bus or a wired local area network.

The aim of pulse modulation methods is to transfer a narrowband analog signal, for example

a phone call over a wideband baseband channel or, in some of the schemes, as a bit streamover another digital transmission system.

2.3 Digital Modulation

In digital modulation, an analog carrier signal is modulated by a discrete signal.

Digital modulation methods can be considered as digital-to-analog conversion, and the

corresponding demodulation or detection as analog-to-digital conversion. The changes inthe carrier signal are chosen from a finite number of M alternative symbols (the modulation

alphabet).

According to one definition ofdigital signal, the modulated signal is a digital signal,and according to another definition, the modulation is a form ofdigital-to-analog

conversion. Most textbooks would consider digital modulation schemes as a form of digitaltransmission, synonymous to data transmission; very few would consider it as analog

transmission.

2.4 Fundamental Digital Modulation Methods:

The most fundamental digital modulation techniques are based on keying:
http://en.wikipedia.org/wiki/Digitalhttp://en.wikipedia.org/wiki/Bandpasshttp://en.wikipedia.org/wiki/Channel_(communications)http://en.wikipedia.org/wiki/Public_switched_telephone_networkhttp://en.wikipedia.org/wiki/Bandpass_filterhttp://en.wikipedia.org/wiki/Analog_signalhttp://en.wikipedia.org/wiki/Basebandhttp://en.wikipedia.org/wiki/Lowpasshttp://en.wikipedia.org/wiki/Channel_(communications)http://en.wikipedia.org/wiki/Frequency_division_multiplexinghttp://en.wikipedia.org/wiki/Line_codinghttp://en.wikipedia.org/wiki/Basebandhttp://en.wikipedia.org/wiki/Serial_bushttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Narrowbandhttp://en.wikipedia.org/wiki/Widebandhttp://en.wikipedia.org/wiki/Digital_transmissionhttp://en.wikipedia.org/wiki/Digitalhttp://en.wikipedia.org/wiki/Demodulationhttp://en.wikipedia.org/wiki/Digital_signalhttp://en.wikipedia.org/wiki/Digital_signalhttp://en.wikipedia.org/wiki/Digital-to-analog_conversionhttp://en.wikipedia.org/wiki/Digital-to-analog_conversionhttp://en.wikipedia.org/wiki/Digital_transmissionhttp://en.wikipedia.org/wiki/Digital_transmissionhttp://en.wikipedia.org/wiki/Data_transmissionhttp://en.wikipedia.org/wiki/Analog_transmissionhttp://en.wikipedia.org/wiki/Analog_transmissionhttp://en.wikipedia.org/wiki/Keying_%28telecommunications%29http://en.wikipedia.org/wiki/Keying_%28telecommunications%29http://en.wikipedia.org/wiki/Analog_transmissionhttp://en.wikipedia.org/wiki/Analog_transmissionhttp://en.wikipedia.org/wiki/Data_transmissionhttp://en.wikipedia.org/wiki/Digital_transmissionhttp://en.wikipedia.org/wiki/Digital_transmissionhttp://en.wikipedia.org/wiki/Digital-to-analog_conversionhttp://en.wikipedia.org/wiki/Digital-to-analog_conversionhttp://en.wikipedia.org/wiki/Digital_signalhttp://en.wikipedia.org/wiki/Digital_signalhttp://en.wikipedia.org/wiki/Demodulationhttp://en.wikipedia.org/wiki/Digitalhttp://en.wikipedia.org/wiki/Digital_transmissionhttp://en.wikipedia.org/wiki/Widebandhttp://en.wikipedia.org/wiki/Narrowbandhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Serial_bushttp://en.wikipedia.org/wiki/Basebandhttp://en.wikipedia.org/wiki/Line_codinghttp://en.wikipedia.org/wiki/Frequency_division_multiplexinghttp://en.wikipedia.org/wiki/Channel_(communications)http://en.wikipedia.org/wiki/Lowpasshttp://en.wikipedia.org/wiki/Basebandhttp://en.wikipedia.org/wiki/Analog_signalhttp://en.wikipedia.org/wiki/Bandpass_filterhttp://en.wikipedia.org/wiki/Public_switched_telephone_networkhttp://en.wikipedia.org/wiki/Channel_(communications)http://en.wikipedia.org/wiki/Bandpasshttp://en.wikipedia.org/wiki/Digital


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In the case ofPSK (phase-shift keying), a finite number of phases are used.

In the case ofFSK (frequency-shift keying), a finite number of frequencies are used.

In the case ofASK (amplitude-shift keying), a finite number of amplitudes are used.

In the case ofQAM (quadrature amplitude modulation), a finite number of at least two

phases, and at least two amplitudes are used.

In QAM, an inphase signal (the I signal, for example a cosine waveform) and a

quadrature phase signal (the Q signal, for example a sine wave) are amplitude modulated with a

finite number of amplitudes, and summed. It can be seen as a two-channel system, each channel

using ASK. The resulting signal is equivalent to a combination of PSK and ASK.

In all of the above methods, each of these phases, frequencies or amplitudes are assigned

a unique pattern of binary bits. Usually, each phase, frequency or amplitude encodes an equalnumber of bits. This number of bits comprises the symbol that is represented by the particular

phase, frequency or amplitude.

If the alphabet consists of alternative symbols, each symbol represents a

message consisting of N bits. If the symbol rate (also known as the baud rate) is

symbols/second (or baud), the data rate is bit/second.

For example, with an alphabet consisting of 16 alternative symbols, each symbol

represents 4 bits. Thus, the data rate is four times the baud rate.

In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is

constant, the modulation alphabet is often conveniently represented on a constellation diagram,

showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-

axis, for each symbol.
http://en.wikipedia.org/wiki/Phase-shift_keyinghttp://en.wikipedia.org/wiki/Frequency-shift_keyinghttp://en.wikipedia.org/wiki/Amplitude-shift_keyinghttp://en.wikipedia.org/wiki/Quadrature_amplitude_modulationhttp://en.wikipedia.org/wiki/Binary_numeral_systemhttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Symbol_ratehttp://en.wikipedia.org/wiki/Baudhttp://en.wikipedia.org/wiki/Baudhttp://en.wikipedia.org/wiki/Constellation_diagramhttp://en.wikipedia.org/wiki/Constellation_diagramhttp://en.wikipedia.org/wiki/Baudhttp://en.wikipedia.org/wiki/Baudhttp://en.wikipedia.org/wiki/Symbol_ratehttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Binary_numeral_systemhttp://en.wikipedia.org/wiki/Quadrature_amplitude_modulationhttp://en.wikipedia.org/wiki/Amplitude-shift_keyinghttp://en.wikipedia.org/wiki/Frequency-shift_keyinghttp://en.wikipedia.org/wiki/Phase-shift_keying


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Binary Phase Shift Keying

3.1 Introduction

Communication is the activity of conveying information. Modulation is the process of

varying one or more properties of a high-frequency periodic waveform, called thecarrier signal,with a modulating signal which typically contains information to be transmitted.

There are two types of modulation analog and digital. Binary Phase Shift Keying (BPSK)is one digital modulation technique where the phase of the carrier signal is varied according to

the digital message signal.

3.2 Modulation Technique

Input Bit Stream Sum modulated

signal

oscillator

Fig 3.1 Block diagram of BPSK modulator

The general form for BPSK follows the equation:

(3.2.1)

This yields two phases, 0 and . In the specific form, binary data is often conveyed with thefollowing signals:

Phase

Shifter

Serial to

Parallel

Converter
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for binary "0"

(3.2.2)

for binary "1"

(3.2.3)

wherefc is the frequency of the carrier-wave.

Here the carrier signal is used to modulate bit 1 and the shifted carrier is used tomodulate bit 0.

Fig 3.2 waveform of BPSK modulation

The main parts of a BPSK modulator is a VCO for the generation of carrier signal, aphase shifter for the generation of phase-shifted carrier and the main modulator part.


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The constellation diagram is shown in Fig 3.3

Fig 3.3 BPSK constellation diagram

3.3 Demodulation Technique

Modulated signal 1

0

Carrier

Fig 3.4 Block diagram of BPSK demodulator

The information in PSK signals resides in the carrier phase. Envelope detection can not

be used for the demodulation of BPSK signal as the envelope stays constant for both 1 and 0.

Therefore, coherent detection is used for the demodulation of BPSK signals. Here the modulated

signal is multiplied with the carrier, passed through an LPF and then sent to a decision device

which is nothing but a comparator. If the input to the decision device is greater than zero then it

decides in favour of bit 1 whereas if it is less than zero it decides in favour of bit 0.

The bit error rate (BER) of BPSK in AWGN can be calculated as

or (3.3.1)

LPF Decision
http://en.wikipedia.org/wiki/Bit_error_ratehttp://en.wikipedia.org/wiki/AWGNhttp://translate.googleusercontent.com/translate_c?hl=en&rurl=translate.google.co.in&sl=nl&tl=en&u=http://nl.wikipedia.org//commons.wikimedia.org/wiki/File:BPSK_Gray_Coded.svg&usg=ALkJrhi6ecILWOm-6pA0xw3y7SHP3caxzAhttp://translate.googleusercontent.com/translate_c?hl=en&rurl=translate.google.co.in&sl=nl&tl=en&u=http://nl.wikipedia.org//commons.wikimedia.org/wiki/File:BPSK_Gray_Coded.svg&usg=ALkJrhi6ecILWOm-6pA0xw3y7SHP3caxzAhttp://translate.googleusercontent.com/translate_c?hl=en&rurl=translate.google.co.in&sl=nl&tl=en&u=http://nl.wikipedia.org//commons.wikimedia.org/wiki/File:BPSK_Gray_Coded.svg&usg=ALkJrhi6ecILWOm-6pA0xw3y7SHP3caxzAhttp://en.wikipedia.org/wiki/AWGNhttp://en.wikipedia.org/wiki/Bit_error_rate


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Since there is only one bit per symbol, this is also the symbol error rate .

Oscillator

4.1 Overview of Oscillator

An electronic oscillator is an electronic circuit that produces a repetitive electronic signal,often a sine wave or a square wave. They are widely used in many electronic devices. Common

examples of signals generated by oscillators include signals broadcast by radio and televisiontransmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by

electronic beepers and video games.

Oscillators are often characterized by the frequency of their output signal: an audio

oscillator produces frequencies in the audio range, about 16 Hz to 20 kHz. An RF oscillator

produces signals in the radio frequency (RF) range of about 100 kHz to 100 GHz. A low-

frequency oscillator (LFO) is an electronic oscillator that generates a frequency below 20 Hz.This term is typically used in the field of audio synthesizers, to distinguish it from an audiofrequency oscillator. The mathematical expression for oscillation is given by

(4.1.1)

This equation is linear in . By assumption, the parameters and depend only on time

and do notdepend on the state of the oscillator. In general, and/or are assumed tovary periodically, with the same period.

4.2Principle of Operation

An oscillator operates on the principle of positive feedback. The block diagram of a

positive feedback network is given below:

Vi(s) Vo(s)

Fig 4.1 Block diagram of a positive feedback network

G(s)

H(s)
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The transfer function is given by

T(s) = Vo(s) / Vi(s) = G(s) / [1+G(s)H(s)] (4.2.1)

Now, if the feedback factor G(s)H(s) = -1 , then T(s) becomes infinite and we get a very largeoutput with negligible input. This is the Barkhausen Criterion for oscillation.

Taking G(s)H(s) = x and expanding binomially, eqn (4.2.1) can be written as

Vo(s) = Vi(s)G(s) .[1+x+x2+x

3+x

4+. upto infinite.] (4.2.2)

So , when x=1 , Vo(s) = infinite.

Oscillations will not be sustained if the value of feedback factor x is less than unity.

In practice, the feedback factor is always slightly less than unity for the stability purpose.

So the eqn (4.2.2) can be written as (neglecting higher order components)

Vo(s) = Vi(s)G(s) . [1+x+x2] (4.2.3)

4.3 Stability of Oscillator

Stability of any electronic component can be expressed in terms of its Bode plot.A Bode

plot is a parametric plot of a transfer function used in automatic control and signal processing.

Illustrated in Fig 4.2, the situation can be viewed as excessive loop gain at the frequency

for which the phase shift reaches -1800 or, equivalently, excessive phase at the frequency for

ehich the loop gain drops to unity. Thus, to avoid instability, we must minimize the total phase

shift so that for |H| = 1, H is still more positive than / -1800.

20log|H(w)|

Excessive Gain

0 w (log scale)

0 w (log scale)

-1800

/ H(w) Excessive Phase
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Fig 4.2 Bode Plot of an Unstable System

It is also instructive to plot the location of poles of a closed loop system on a

complex plane. If the poles lie on the right half plane then the system will oscillate. If

they lie on the imaginary axis then the sytem will sustain oscillations. If the poles lie on

the left half then the oscillations will die out.

Fig 4.3 Pole Location of Stable & Unstable System

4.4 Types of Oscillators

There are two main types of electronic oscillator: the linear or harmonic oscillator and

the nonlinear or relaxation oscillator.

1.Linear oscillator:
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The harmonic, orlinear, oscillator produces a sinusoidal output.

The basic form of a linear oscillator is an electronic amplifier connected in a feedback

loop with its output fed back into its input through a frequency selective electronic filter to

provide positive feedback. When the power supply to the amplifier is first switched on, the

amplifier's output consists only ofnoise. The noise travels around the loop and is filtered and re-amplified until it increasingly resembles a sine wave at a single frequency.

Linear oscillator circuits can be classified according to the type of frequency selective filterthey use in the feedback loop:

In anRC oscillatorcircuit, the filter is a network ofresistors and capacitors. RCoscillators are mostly used to generate lower frequencies, for example in the audio range.

Common types of RC oscillator circuits are the phase shift oscillator and the Wien bridge

oscillator.

In anLC oscillatorcircuit, the filter is a tuned circuit (often called a tank circuit)

consisting of an inductor (L) and capacitor (C) connected together Charge flows back andforth between the capacitor's plates through the inductor, so the tuned circuit can store

electrical energy oscillating at its resonant frequency. There are small losses in the tank

circuit, but the amplifier compensates for those losses and supplies the power for the

output signal. LC oscillators are often used at radio frequencies, when a tunablefrequency source is necessary, such as in signal generators, tunable radio transmitters and

the local oscillators in radio receivers. Typical LC oscillator circuits are the Hartley,

Colpitts and Clapp circuits.

In acrystal oscillatorcircuit the filter is a piezoelectric crystal (commonly a quartz

crystal). The crystal mechanically vibrates as a resonator, and its frequency of vibrationdetermines the oscillation frequency. Crystals have very high Q-factor and also better

temperature stability than tuned circuits, so crystal oscillators have much better frequency

stability than LC or RC oscillators. They are used to stabilize the frequency of most radiotransmitters, and to generate the clock signal in computers and quartz clocks. Crystal

oscillators often use the same circuits as LC oscillators, with the crystal replacing the

tuned circuit;[2]

the Pierce oscillator circuit is commonly used. Quartz crystals are

generally limited to frequencies of 30 MHz or below. Surface acoustic wave (SAW)devices are another kind of piezoelectric resonator used in crystal oscillators, which can

achieve much higher frequencies. They are used in specialized applications which requirea high frequency reference, for example, in cellular telephones.

In addition to the feedback oscillators described above, which use two-port amplifying active

elements such as transistors and op amps, linear oscillators can also be built using one-portdevices with negative resistance, such as magnetron tubes, tunnel diodes and Gunn diodes. In

these oscillators, a resonator, such as an LC circuit, crystal, or cavity resonator, is connected

across the negative resistance device, and a DC bias voltage is applied to supply energy. The
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negative resistance of the active device can be thought of as cancelling the (positive) effective

loss resistance of the resonator and permitting a sustained oscillation. These circuits are

frequently used for oscillators at microwave frequencies.

These are some of the many linear oscillator circuits:

Armstrong oscillator

Hartley oscillator

Colpitts oscillator

Clapp oscillator

Delay line oscillator

Pierce oscillator (crystal)

Phase-shift oscillator

RC oscillator (Wien Bridge and "Twin-T")

Cross-coupled LC oscillator Vack oscillator Opto-Electronic Oscillator.

2.Relaxation oscillator:

A nonlinear or relaxation oscillator produces a non-sinusoidal output, such as a square,

sawtooth or triangle wave. It contains an energy-storing element (a capacitor or, more rarely, an

inductor) and a nonlinear trigger circuit (a latch, Schmitt trigger, or negative resistance element)

that periodically charges and discharges the energy stored in the storage element thus causingabrupt changes in the output waveform.

Square-wave relaxation oscillators are used to provide the clock signal for sequential

logic circuits such as timers and counters, although crystal oscillators are often preferred for their

greater stability. Triangle wave or sawtooth oscillators are used in the timebase circuits thatgenerate the horizontal deflection signals for cathode ray tubes in analogue oscilloscopes and

television sets. In function generators, this triangle wave may then be further shaped into a close

approximation of a sine wave.

Ring oscillators are built of a ring of active delay stages. Generally the ring has an odd

number of inverting stages, so that there is no single stable state for the internal ring voltages.Instead, a single transition propagates endlessly around the ring.

Types of relaxation oscillator circuits include:

multivibrator

ring oscillator

delay line oscillator
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rotary traveling wave oscillator.

Voltage controlled oscillator5.1 Overview

A voltage-controlled oscillator or VCO is an electronic oscillator designed to be

controlled in oscillationfrequency by a voltage input. The frequency of oscillation is varied by

the applied DC voltage, while modulating signals may also be fed into the VCO to cause

frequency modulation (FM) or phase modulation (PM); a VCO with digital pulse output may

similarly have its repetition rate (FSK, PSK) or pulse width modulated (PWM).

It consists of a varactor diode whose capacitance varies with the applied voltage. So by

changing the input voltage the oscillation frequency can be varied.

wout

w2

w1 KVCO wout = w0 +KVCOVcont

w0

Vcont

V1 V2

Fig 5.1 VCO Response Curve

3.2Types of VCOs

VCOs can be generally categorized into two groups based on the type of waveform

produced: 1) harmonic oscillators, and 2) relaxation oscillators.

Harmonic oscillatorsgenerate a sinusoidal waveform. They consist of an amplifier that

provides adequate gain and a resonant circuit that feeds back signal to the input. Oscillation

occurs at the resonant frequency where a positive gain arises around the loop. Some examples ofharmonic oscillators are crystal oscillators and LC-tank oscillators. When part of the resonant
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circuit's capacitance is provided by a varactor diode, the voltage applied to that diode varies the

frequency.

Relaxation oscillators can generate a sawtooth or triangular waveform. They are

commonly used in monolithic integrated circuits (ICs). They can provide a wide range of

operational frequencies with a minimal number of external components. Relaxation oscillatorVCOs can have three topologies: 1) grounded-capacitor VCOs, 2) emitter-coupled VCOs, and 3)

delay-based ring VCOs. The first two of these types operate similarly. The amount of time in

each state depends on the time for a current to charge or discharge a capacitor. The delay-basedring VCO operates somewhat differently however. For this type, the gain stages are connected in

a ring. The output frequency is then a function of the delay in each of stages.

Harmonic oscillator VCOs have these advantages over relaxation oscillators.

Frequency stability with respect to temperature, noise, and power supply is much betterfor harmonic oscillator VCOs.

They have good accuracy for frequency control since the frequency is controlled by a

crystal or tank circuit.

A disadvantage of harmonic oscillator VCOs is that they cannot be easily implemented in

monolithic ICs. Relaxation oscillator VCOs are better suited for this technology. Relaxation

VCOs are also tunable over a wider range of frequencies.

5.3 VCO time-domain equations

ftuning(t)=K0.vin(t) (5.2.1)

ftuning(t)dt=out(t) (5.2.2)

K0 is called the oscillator gain. Its units are hertz per volt.

ftuning(t) is the symbol for the time-domain waveform that is the VCO's tunable

frequency component.

out(t) is the symbol for the time-domain waveform that is the VCO's output

phase.

Vin(t) is the time-domain symbol of the control (input) voltage of the VCO; it is

sometimes also represented as vtune(t) .

5.4 VCO frequency-domain equations

Ftuning(s)=k0.vin(s) (5.3.1)

Ftuning(s)


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s =out(s) (5.3.2)

Analog applications such as frequency modulation and frequency-shift keying often need

to control an oscillator frequency with an inputa voltage-controlled oscillator (VCO). Thefunctional relationship between the control voltage and the output frequency may not be linear.

Over small ranges, the relationship is approximately linear, and linear control theory can be used.

5.5 VCO Parameters

The important parameters of a VCO are as follows:

Center Frequency

Tuning Range

Tuning Linearity

Output Amplitude

Power Dissipation

Supply and Common-Mode Rejection

Output Signal Purity

5.6 VCO Applications

VCOs are used in:

Function generators,

The production ofelectronic music, to generate variable tones,

Phase-locked loops,

Frequency synthesizers used in communication equipment.

Voltage-to-Frequency converters are voltage-controlled oscillators, with a highly linear

relation between applied voltage and frequency. They are used to convert a slow analog signal

(such as from a temperature transducer) to a digital signal for transmission over a long distance,since the frequency will not drift or be affected by noise. VCOs may have sine and/or square

wave outputs. Function generators are low-frequency oscillators which feature multiple

waveforms, typically sine, square, and triangle waves. Monolithic function generators arevoltage-controlled. Analog phase-locked loops typically contain VCOs. High-frequency VCOsare usually used in phase-locked loops for radio receivers. Phase noise is the most important

specification for them. Low-frequency VCOs are used in analog music synthesizers. For these,

sweep range, linearity, and distortion are often most important specs.
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Phase shifter

6.1 Overview

It is an electronic device that is use to shift the phase of any signal. In the BPSK

modulation scheme, we need to use 2 phases for the two bits 1 & 0.So we need a phase shifterto provide the two phases of the same carrier signal. Thus we dont need two carrier signals, onlyone signal is enough.

If the input to the phase shifter is A.sin (wt) then the output of the phase shifter will be

A.sin (wt + ). where, is the required phase shift.

6.2 Classification

Active versus passive: Active phase shifters provide gain, while passive phase shiftersare lossy.

o Active:

Applications: active electronically scanned array(AESA), passiveelectronically scanned array (PESA)

Gain: The phase shifter amplifies while phase shifting Noise figure (NF)

Reciprocity: not reciprocal

o Passive:

Applications: active electronically scanned array(AESA), passiveelectronically scanned array (PESA)

Loss: the phase shifter attenuates while phase shifting

NF: NF = loss

Reciprocity: reciprocal

Analog versus digital:

o

Analog phase shifters provide a continuously variable phase shift or time delay.o Digital phase shifters provide a discrete set of phase shifts or time delays.

Discretization leads to quantization errors. Digital phase shifters require parallel

bus control.

Differential, single-ended or waveguide:
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o Differentialtransmission line: A differential transmission line is a balanced two-

conductor transmission line in which the phase difference between currents is 180

degrees. The differential mode is less susceptible to common mode noise andcross talk.

Antenna selection: dipole, tapered slot antenna (TSA)

Examples: coplanar strip, slotlineo Single-ended transmission line: A single-ended transmission line is a two-

conductor transmission line in which one conductor is referenced to a common

ground, the second conductor. The single-ended mode is more susceptible to

common-mode noise and cross talk.

Antenna selection: double folded slot (DFS), microstrip, monopole

Examples: CPW, microstrip, stripline

o Waveguide

Antenna selection: waveguide, horn
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Current Mode Device7.1 Introduction

A Current Mode Device is a device where the output current of the device is a function of

the input voltage. There is often a demand in analogue signal processing for amplifier circuitsthat posses well defined current signal processing properties .Furthermore current amplifier

based circuits can offer certain high performances properties such as speed, bandwidth, accuracy

which make them more acceptable than voltage amplifier. A further consequence of the

development of current mode analogue signal processing has been the emergence of newanalogue building blocks ranging from the current conveyor and current feedback op-amps

through to sampled data current circuits such as dynamic current mirrors and analogue neuralnetwork.

7.2 Current Conveyor

A current conveyor is a four (possibly five) terminal device which when arranged with

other electronic elements in specific circuit configurations can perform many useful analog

signal processing functions.

iY

VY Y iZ

CC Z

VX X

iX

Fig 7.1 Black box representation of the current conveyor

The current conveyor (CCI), as initially introduced is a 3-port device whose black-box

representation can be seen in Fig 7.1. the operation of this device is such that if a voltage isapplied to input terminal Y, an equal potential will appear on the input terminal X. In a similar

fashion, an input current I being forced into terminal X will result in an equal amount of current

flowing into terminal Y. As well, the current I will be conveyed to output terminal Z such that

terminal Z has the characteristics of a current source, of value I, with high output impedance. As

can be seen, the potential of X, being set up by that of Y, is independent of the current being

forced into port X. Similarly, the current through input Y, being fixed by that of X, is


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independent of the voltage applied at Y. Thus the device exhibits a virtual short-circuit input

characteristic at port X and a dual virtual open-circuit input characteristic at port Y.

In mathematical terms, the input-output characteristics of CCI can be described by the

following hybrid equation

iY 0 1 0 VY

VX = 1 0 0 iX

IZ 0 +1 0 VZ (7.2.1)

Note that the + sign applies for the CCI in which both Z and X flow into the convetor,

denoted CCI+. Thesign apply for the opposite polarity case, denoted CCI-. To visualize the

interaction of the port voltages and currents described by the bove matrix equation the nullator-norator representation shown in Fig 7.2 may be helpful. In this figure, single ellipse is used to

represent the nullator element and two intersecting ellipses to represent the norator element. The

nullator element has constitutive equations V=0 and I=0 whereas the norator has an arbitrary

voltage-current relationship.

I

Y

Z

X I

I

Fig 7.2 Nullator-norator representation of CCI

Clearly, the nullator element is used to represent the virtual short circuit apparent

between the X and Y terminals. Also included in this equivalent circuit are two dependant

current sources. These are used to convey the current at port X to ports Y and Z.

A discrete first-order implementation of the current conveyor is depicted in Fig 7.3.

Assuming that all transistors are matched and that all have high current gain, it can be shown that


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the currents through transistors M3-M5 are equal. This forces transistors M1 and M2 to have

equal currents and thus equal VGSdrops. Thus X and Y track each other in both voltage and

current

iY iX

Y X

vY vX

M1 M2 iZ

Z

vZ

M4 M5

M3

VSS

Fig 7.3 First-order CMOS implementation of CCI

To increase the versatility of the current conveyor, a second version in which no currentflows in terminal Y, was introduced. This building block has since proven to be more useful than

CCI. Utilizing the same block diagram representation of Fig 7.1, CCII is described by

iY 0 0 0 VY

VX = 1 0 0 iX

IZ 0 +1 0 VZ (7.2.2)

Thus, terminal Y exhibits an infinite input impedance. The voltage at X follows that

applied to Y, thus X exhibits a zero input impedance. The current supplied to X is conveyed to

the high-impedance output terminal Z where it is supplied with either positive polarity or

negative polarity.


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In terms of a nullor, the port behavior of the second generation current conveyor can be

depicted as shown in Fig 7.4

Y

X Z

Fig 7.4 Nullator-norator representation of CCII

In the case of CCII, the dependant current source is redundant; current flowing into

terminal X must flow out of terminal Z. Hence, the equivalent circuit of CCII can be represented

with a single nullor element as shown in Fig 7.4.

The CCII may be viewed as an ideal MOS. Gate as terminal Y, source as terminal X and

drain as terminal Z.

7.3 Switched Capacitor

Analog sampled-data signal processing has been dominated for the past decade by the

switched capacitor technique. Switched capacitors gained favour as a technique for

implementing active filters capable of greater precision and compactness than earlier active-RC

filters, especially in low frequency applications.

Most switched capacitor filter structures have resulted from the substitution of an active-

RC filters continuous-time integrators by switched capacitor counterparts. This approach hasbeen applied to state-variable filters and to filters which simulate the nodal voltages of lossless

ladder prototypes.


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C

2 1C 1

V1

1 2 V0

Fig 7.5 Switched capacitor non-inverting integrator

Switched capacitor integrator is shown in Fig 7.5. On phase 2of the non-overlappingclock period (n-1), the charge on capacitor C holds the output voltage at V0(n-1) while capacitor

1C is charged to V1(n-1). The next clock phase is 1 of period(n), and capacitor1C isdischarged into capacitor C causing the output voltage to charge to V0(n). It is easily shown that

V0(n) = V0(n-1) + 1V1(n-1) (7.3.1)

which gives the z-domain transfer function

H1(z) = V0(z) = 1z-1

V1(z) 1-z-1 (7.3.2)

This is the Forward Euler z-transform of a non-inverting integrator (H(s)=1/sRC) where

1=T/RC.

7.4 Differential Pair Transconductor

The simplest and most widely used transconductor is the source-coupled differential pair.

In addition to its obvious simplicity, the differential pair offers a true differential input and can

readily achieve both positive and negative transconductance values. With a slight increase in

complexity to implement common-mode feedback, this enables the implementation of a fully-

balanced architecture, thus improving the dynamic range, PSRR, and CMRR. Furthermore, the

inherent symmetry of the differential amplifier tends to reduce offsets and drift. While offering

excellent high frequency performance and low noise, its large signal characteristics are


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nonlinear. As a result, it can be shown that both the dynamic range and the efficiency of the

differential pair are limited.

ID1 ID2

M1 M2

Vid

ISS

VSS

Fig 7.6 Differential pair transconductor

The basic source-coupled differential pair is shown in Fig 7.6. Using the simplified

square-law relationship for a MOSFET in the saturation region and assuming M1 and M2 areperfectly matched, the output current is given by

I0= ID1- ID2= 2ISSK Vid - (K/2ISS). V2

id Vid < ISS/K

(7.4.1)

= ISS sgn(Vid) Vid > ISS/K

Clearly, the input stage is linear only over a limited range of differential input voltage.

The nonlinearity, which is a function of ISS, causes two problems. First, notice that as the signal

level is increased the transfer function becomes more nonlinear. Therefore, large input signals

will result in harmonic distortion and spurious signals being generated due to intermodulation.

Second, since the transconductance of the input stage equals the slope of the I 0 vs. Vid

characteristic curve, gm decreases as the signal level increases. This makes the transconductance

a function of differential input signal level.


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The relationship between gm and Vid can be developed by taking the derivative of (7.4.1)

with respect to Vid, yielding

gm= 2ISSK [ 1- (K/ISS). V2

id] / 1- (K/2ISS). V2

id (7.4.2)

7.5 Cross-Coupled Differential Pair

A substantial increase in linearity can be obtained by simply cross-coupling two

differential pairs as shown in Fig 7.7. By properly scaling the ratio of W/Ls and bias currents,approximate cancellation of the remaining odd order nonlinearities can be achieved.

M1 M3 M4 M2

K1 K2 K3 K4

Vid

ISS1 ISS2

VSS

Fig 7.7 Cross-coupled differential pairs

The linear term is proportional to 2ISSK whereas the nonlinear term is proportional toK

3/2/ ISS . Therefore, nonlinearity cancellation is accomplished by scaling the W/L ratios and

tail currents of the differential pairs according to

[(W/L)1/ (W/L)2]3/2

= [ISS1/ISS2]1/2

(7.5.1)

providing (W/L)1 = (W/L)2and ISS1 = ISS2.This makes the coefficient of the nonlinear terms

cancel when the output currents are subtracted resulting in a linear transconductance given by

gm =gm1 =gm2=2ISS1K1 - 2ISS2K2 (7.5.2)


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7.6 Operational Transconductance Amplifier

An OTA is a voltage controlled current source, more specifically the term operationalcomes from the fact that it takes the difference of two voltages as the input for the current

conversion.

The ideal transfer characteristic is therefore,

IO =gm . (V+V) (7.6.1)

or, by taking the pre-computed difference as the input,

IO =gm. Vin (7.6.2)

with the ideally constant transconductancegm as the proportionality factor between the two.

Inreality the transconductance is also a function of the input differential voltage and dependent

on temperature.

Fig 7.8 (a) Schematic of OTA (b) Equivalent circuit of OTA


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The characteristics of an ideal OTA is as follows:

Input Impedance (Zin) = Infinite

Output Impedance (Z0) =

Inverting input current = - Non-inverting input current =I0

Bandwidth =infinite


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Fig 7.9 Structure of proposed OTA

The proposed CMOS OTA is presented in Fig 7.9. It has differential inputs and

differential outputs, which allows the circuit to be used in both positive and negative feedback

system configurations.


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Rch1 Z1

vgs1 = vin+

id1

id2 vd1 Z2

vin+

iout- = ip + in

Cin id3 Z3

vd4

id4

vgs4 =vin+ -vd9 Rch4 Z4

vd9

Z9

Fig 7.10 High frequency half equivalent circuit model of OTA

Fig 7.10 shows a high frequency equivalent circuit of the left-half of the OTA in Fig 7.9,

where the transistor parasitic are modeled with an input capacitance Cin and impedances Z1~4and

Z9. The equivalent circuit model can be simplified to one shown in Fig 7.11. Here the top

transistor T1is modeled by a variable channel resistance Rch1 because it operates in triode. Its RF

currentid1is given by

id1 =-gm1 vin+ (7.6.3)

where vin+ is one of the differential RF input signals and the transconductance gm1 can be

calculated using the following expression derived from the short-channel drain current in thelinear region

gm = dId / dVgs = Cox (W/L) Vds/( 1 + Vds /(Esat L)) (7.6.4)


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ip Zp

vin+ iout-

Cin

in Zn

Fig 7.11 Simplified circuit model of OTA

Transistor T2 in the pMOS cascade works in the saturation region and its RF current is given by

id2 = - gm2 vgs2 (7.6.5)

where vgs2 is the gate-source voltage, and the transconductance gm2 is calculated using the

equation

gm = dId / dVgs = vsatCox W [1 - ( Esat L /(Vgs- Vt + Esat L))2

] (7.6.6)

The gate voltage of this pMOS device has an inverse polarity relative to its source voltage v d1. If

they are assumed to be exactly offset from each other, its gate-source voltage vgs2becomes -2vd1.

Then (7.6.5) can be changed to

id2 = 2 gm2 vd1 (7.6.7)

In a similar fashion, the RF currents in the nMOS cascode are given by

id3 = 2 gm3 vd4 (7.6.8)

id4 = - gm4(vin+ - vd9 ) (7.6.9)

where vd4 and vd9are the drain voltages of T4 and T9 respectively.

The output currents can be derived from the equivalent circuit model as

ip= - gm1 vin+ (Z1 + 2 gm2 Z1 Z2) /( Z1 + Z2 + 2 gm2 Z1 Z2) (7.6.10)

in= - gm4 vin+ (Z4+ 2 gm3 Z3 Z4) /( Z3 + Z4 + 2 gm3 Z3 Z4) (7.6.11)

The overall transconductance is found to be

gm = ( iout+ - iout- ) / ( vin+ - vin- )

= - (ip + in) / vin+


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= gm1(Z1 + 2 gm2 Z1 Z2) /( Z1 + Z2 + 2 gm2 Z1 Z2)

+ gm4(Z4+ 2 gm3 Z3 Z4) / ( Z3 + Z4 + 2 gm3 Z3 Z4) (7.6.12)

7.7 Reasons For Choosing OTA as Main Building Block

Basically OTA is a voltage controlled current mode device & it is advantageous over

other current mode device like JFET,MOSFET in the sense that OTA has the much higher

capability of withstanding the noise & atmospheric attenuation.

It has linear transconductance characteristics with respect to the amplifier bias current,

this can be considered as a gain controlled block

It has a good power supply rejection & common mode rejection than any differential

amplifier, above other mentioned

This is the cause of choosing this device as a basic building block of our modulator.

7.8 Model Parameter Of MOS Used For Simulation

Supply Voltage: 1.2 Volts

Constant Bias Current: 10mAFor PMOS:

W/L Ratio 120/10.5

Threshold Voltage: -0.293V

Oxide Thickness: 2.85 E-09For NMOS:

W/L Ratio 20/1.5

Threshold Voltage: 0.318VOxide Thickness: 2.81 E-09

For both MOS s:

Gate Source capacitance 1 microfarad

Gate Drain capacitance 10 microfarad

Body Drain capacitance 100 picofarad

Body Source capacitance 50 picofarad

Block Diagrams

8.1 Voltage Controlled Oscillator

OUTPUT


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INPUT VOLTAGE

Fig 8.1Block Diagram of VCO using OTA

8.2 Phase Shifter

INPUT

OUTPUT

Fig 8.2Block Diagram of PhaseShifter using OTA

8.3 BPSK Modulator

BIT 1


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OUTPUT VOLTAGE

CARRIER[A sin(wct)]

BIT 0

SHIFTED CARRIER[A cos(wct)]

Fig 8.3 Block Diagram of BPSK Modulator using OTA

Simulated Output

9.1 Lineariaty Check


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Fig 9.1 Waveform for Linearity Check

9.2 Voltage Controlled Oscillator


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Fig 9.2 Waveform for VCO

Input Voltage: 5mv (DC)

Output Frequency: 25 Hz


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9.3 Phase Shifter

Fig 9.3 Waveform for Phase Shifter

Input Voltage: 4 V peak to peak Output Voltage: 0.2 V peak to peakInput Frequency: 50 Hz Output Frequency: 50 Hz

Input Phase: 00 Output Phase: 900


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9.4 BPSK Modulator

Fig 9.4 Waveform for BPSK Modulation Bit 1


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Fig 9.5 Waveform for BPSK Modulation Bit 0


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Spread Spectrum Moculation

10.1 DESIGN OF LFSR

An LFSR is a shift register that, when clocked, advances the signal through the register

from one bit to the next most-significant bit. Some of the outputs are combined in exclusive-ORconfiguration to form a feedback mechanism. A linear feedback shift register can be formed by

performing exclusive-OR on the outputs of two or more of the flip-flops together and feeding

those outputs back into the input of one of the flip-flops.

Fig 10.1 Block Diagram of Linear Feedback Shift Register


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10.2 DESIGN OF FCSR

In sequence design, a Feedback with Carry Shift Register (FCSR) is the arithmetic or

with carry analog of a Linear Feedback Shift Register (LFSR).An 8 bit FCSR consists of 4LFSRs. The output of each LFSR is multiplied with a fixed integer and then added together. The

sum is then divided by an integer giving the 8bit output of the FCSR.

In this project, I have multiplied the output of the LFSRs by 7,9,4,2 respectively and then divided

the sum by 15.

Fig 10.2 Block Diagram of Feedback Carry Shift Register

10.3 DESIGN OF MODULATOR

According to the output of the FCSR different frequencies are chosen from a set of

frequencies, which will be the carrier frequency. Now, the baseband signal is phase modulatedby this carrier. In PSK bit 1 is transmitted by cosine waveform & bit 0 is transmitted by cosine

waveform shifted by 90 degrees. In this part, i have written a C program for cosine waveform &

merged it with the FCSR program to generate the modulated signal. This program is not yet

completed & is in progress.


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Program & Output

11.1 LFSR PROGRAM#include

int xor(int,int);

main(){

int a0,a1,a2,a3,i,t,g;

a1=a2=a3=0;

a0=1;

for(i=1;i


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0101

1010

1101

1110

11110111

0011

0001

1000

11.3 FCSR PROGRAM

#include

int xor(int,int);

int mult (int,int,int,int,int,int,int,int);

main(){

int a0,a1,a2,a3,b0,b1,b2,b3,c0,c1,c2,c3,d0,d1,d2,d3;

int t1,t2,t3,t4,g1,g2,g3,g4;

int m1,m2,m3,m4;

int e,f,i,g,s,x[8];

a1=a2=a3=b0=b2=b3=c0=c1=c3=d0=d1=d2=0;

a0=b1=c2=d3=1;

for(i=0;i


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c1=c0;

c0=xor(t3,g3);

t4=d3;

g4=d2;

d3=d2;d2=d1;

d1=d0;

d0=xor(t4,g4);

m1=mult(a3,a2,a1,a0,0,1,1,1);

m2=mult(b3,b2,b1,b0,1,0,0,1);

m3=mult(c3,c2,c1,c0,0,1,0,0);

m4=mult(d3,d2,d1,d0,0,0,1,0);

s=m1+m2+m3+m4;

e=s/15;

f=s%15;

for(j=0;j


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return(f);

}

11.4 FCSR PROGRAM OUTPUT

the 1th fcsr output is

00001000the 2th fcsr output is

00001001


00010000


00010010


00010000


00010000


00001111


00010100


00011001


00011010

the 11th fcsr output is00010110


00001100


00000110


00000111


00001010

the 16th fcsr output is00001000


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11.5 COSINE PROGRAM

#include

main(){

int i;

float angle,sum,term;

sum=term=1.0;

printf(enter the angle in degree\n);scanf(%f,&angle);angle=(angle*3.141592654)/180;

for(i=1;i


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m[0]=0.0;

for(i=1;i


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1

5.00000000

5.00000000-0.867094

-4.698861

2.498982

3.830972

-3.829222

-2.500202

4.698554

0.842643


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Applications In Defence

1.This OTA based modulator can be used in Stationary vehicular & portable transreceiver, fast

data modem, tactical antennas on all military platform. Portable transreceiver is used to provide

short-range, two-way radiotelephone voice communication.

2. It can also be used Doppler RADAR which can give the velocity data about a moving or

stationary object using the Doppler effect. A Doppler radar is a specialized radar that makes use

of the Doppler effect to produce velocity data about objects at a distance. It does this by beaming

a microwave signal towards a desired target and listening for its reflection, then analyzing how

the frequency of the returned signal has been altered by the object's motion. This variation gives

direct and highly accurate measurements of the radial component of a target's velocity relative to

the radar. Doppler radars are used in aviation, sounding satellites, meteorology, police speed

guns, radiology, and bistatic radar (surface to air missile).

3.OTA based M_ary communication system is most bandwidth efficient modulation scheme

enable us the less use of the required input power.

4.Because of the wide applicability of bandwidth-efficient modulation to most new satellitesystems, One recent application can be found in the Advanced Extremely High Frequency

(AEHF) program. This OTA based Modulators has been developed for an approach of using

the system in S Band (2 to 4 GHz).

5. The S-Band spectrum has been a bone of contention between terrestrial mobile phone service

providers and backers of satellite mobile services for the last few years. The S band is used by

weather radar, surface ship radar, and some communications satellites, especially those used by

NASA to communicate with the Space Shuttle and the International Space Station. The 10-cm

radar short-band ranges roughly from 1.55 to 5.2 GHz. S band is also used in opticalcommunications, WiMax, Bluetooth. As the proposed OTA works in GHz range so theadvantages of S band can be fully utilized by the OTA based modulator.

Future Areas Of Work

All the works that I have done is related to BPSK modulation. It can be further improvedthrough the introduction of QPSK where four phases of the carrier are used to modulate four
http://en.wikipedia.org/wiki/Radiotelephonehttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Doppler_effecthttp://en.wikipedia.org/wiki/Microwavehttp://en.wiktionary.org/wiki/radialhttp://en.wikipedia.org/wiki/Aviationhttp://en.wikipedia.org/wiki/Meteorologyhttp://en.wikipedia.org/wiki/Radar_gunhttp://en.wikipedia.org/wiki/Radar_gunhttp://en.wikipedia.org/wiki/Radiologyhttp://en.wikipedia.org/wiki/Bistatic_radarhttp://en.wikipedia.org/wiki/Weather_radarhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Communications_satellitehttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Space_Shuttlehttp://en.wikipedia.org/wiki/International_Space_Stationhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/GHzhttp://en.wikipedia.org/wiki/Optical_communicationshttp://en.wikipedia.org/wiki/Optical_communicationshttp://en.wikipedia.org/wiki/Optical_communicationshttp://en.wikipedia.org/wiki/Optical_communicationshttp://en.wikipedia.org/wiki/GHzhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/International_Space_Stationhttp://en.wikipedia.org/wiki/Space_Shuttlehttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Communications_satellitehttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Weather_radarhttp://en.wikipedia.org/wiki/Bistatic_radarhttp://en.wikipedia.org/wiki/Radiologyhttp://en.wikipedia.org/wiki/Radar_gunhttp://en.wikipedia.org/wiki/Radar_gunhttp://en.wikipedia.org/wiki/Meteorologyhttp://en.wikipedia.org/wiki/Aviationhttp://en.wiktionary.org/wiki/radialhttp://en.wikipedia.org/wiki/Microwavehttp://en.wikipedia.org/wiki/Doppler_effecthttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Radiotelephone


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message signals. After QPSK it can be further extended to the concept of Frequency-Hopping

Spread Spectrum.

Frequency hopping is the most popular method of transmitting/receiving radio signals by

periodically switching carrier frequencies. It is realized by using pseudorandom sequences

generated by hopping algorithms. As carrier frequency changes continually, it provides aneffective firewall against the adversarys ability to follow the changes in carrier frequency. Thus,the adversary encounters difficulty to recover the data or information being carried. In addition,

the frequency hopping provides an effective tool for protection against frequency jamming byadversaries.

References

[1] Eduard Sckinger, Walter Guggenbhl A high swing, High-impedance MOS Cascodecircuit. IEEE Journal of Solid-State Circuits,Vol.25,February 1990.

[2] You Zheng, Carlos E. Saavedra Feedforward-Regulated Cascode OTA for GigahertzApplications. IEEE Journal of Circuits and Systems,Vol.55, December 2008.

[3] Chung-Yu Wu, Hong-Sing Kao A 2-V Low Power CMOS Direct-Conversion QuadratureModulator With Integrated Quadrature Voltage-Controlled Oscillator and RF Amplifier for GHz

RF Transmitter Applications. IEEE Journal of Analog and Digital Signal Processing, Vol.49,February 2002.

[4] Abdelouahab Djemouai, Mohamad A. Sawan, Mustapha Slamani New Frequency-LockedLoop Based on CMOS Frequency-to-Voltage Converter: Design and Implementation. IEEEJournal of Analog and Digital Signal Processing, Vol.48, May 2001.

[5] Digital Communication by Simon Haykin, Wiley Student Edition.

[6] Anlogue IC design: the current-mode approach by C.Toumazou, F.J.Lidgey&D.G.Haigh,IEE Circuits And Systems Series 2.

[7] Design Of Analog CMOS IC by Behzad Razavi, Mc Graw Hill Edition.

[8] Atis D Mitra Frequency Hopping an user programmable implementation for PSKmodulated signals

[9] Atis D Mitra and Pradip K Srimani, A New Architecture for User ProgrammableFrequency Hopped Radios for PSK Modulated Signals


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