+_+_ +_+_ a voltage divider circuit produces an output voltage, v 0 that is proportional to the...

inV

oV

+

_

+

_

1R

2R

A voltage divider circuit produces an output voltage, V0 that is

proportional to the input voltage, Vin. The input voltage is

supplied by a voltage source. The constant of proportionality is called the gain of the voltage divider.

21

20

RR

R

V

Vg

in

inV

+

_

1R

2R

3R

4R

1_0V

2_0V

3_0V

By suitably calculating the values of resistances a compound voltage divider circuit can be designed.

inV

oV

+

_

+

_

1R

2R

Knob

Potentiometer is a current or voltage dividing equipment. It incorporates a resistor, which has three terminals; two end terminals, and one middle terminal (knob), as shown in the Figure-6.3. The middle terminal is movable. The extreme ends are connected to the external input voltage signal, and the middle terminal along with one of the end terminal is taken as output. The potentiometer can provide different ratios of input to output resistance, causing a proportionate division of input voltage for various positions of the movable knob.

diode

One cycle

time

time

time

Output voltage

Input voltage

hwV _0

fwV _0

(a)

(b)

(c)

R

Diode-1

inV+

-

Diode-2

hwV _0

ground

R

+

-

inV+

-

(d)

(e)

A

B

C

inV+

-

D-1

D-2

D-3

D-4

R

(f)

A

B

C

D

E

F

G

H

I

I

Rectification is a process by which an alternating current is transformed or rectified into a direct current (DC).

Half-waverectification

Full-waverectification

(d) Half-wave rectifier circuit; (e) Center-tapped FW rectifier ckt; (f) Bridge type FW rectifier ckt.

AC i/p signal

Rectifier circuitinV+

-

RC

+

-

time

fwV _0

(b)

time

hwV _0

(a)Smoothed signal of the Half-wave rectifier

Smoothed signal of the Full-wave rectifier

Capacitor output

Capacitor output

In many occasions, the pulsating output requires smoothing in order to get a constant DC signal. A steady and constant voltage can be obtained by connecting a capacitor at the output of the rectifier circuit.

zenerV

+

-

R

Zener diodeinput

+

_

Zener diodes, a specially designed diode, are used for stabilizing or regulating the voltage in a circuit. The zener diode is always connected in reverse biased condition and are designed to work at the reverse breakdown voltage known as zener voltage. The voltage across the zener diode is reasonably constant over a wide range of input current variations.

R

clippingV

+

-

inV+

- V-1 V-2

D-1D-2

time

Input signal

Clipped signal

+ ve

- ve

(a)

(b)

A B

CD

V-1

V-2 V-2

V-1

A clipping circuit transmits an arbitrary signal within the limits. The signal above and below the limits are suppressed. For this reason clipping circuits are also referred to as voltage limiters. Diodes can be used in the design of clipping circuits.

oVinV

+

-

+

-

R

D

C

Input voltage

time

Output voltage

time

oVinV

+

-

+

-

R

D

C

Input voltage

time

Output voltage

time

Range

Range

Range

Range

(a)

(b)

(c)

(d)

(e)

(f)

Clamping circuits are of two types, namely positive clamper or negative clamper.

Input signal

Clamped output(+ve clamping)

Clamped output(-ve clamping)

input Output

+

-

+

-

inv ovinv

vG 0

input

+

-

inv Output

+

-

ov

inv

vG 0

1G 2G 3G 4G

(a)

(b)

The overall gain of such a multistage amplifier is approximately equal to the product of the individual gains.

nGGGG .....21

+

_

(a) (b)

Input

OutputOutput

Input

+

_

Feedback resistanceFeedback resistanceInput resistance Input resistance

The OPAMP boosts the amplitude significantly and the output voltage is proportional to its input voltage. The OPAMP was originally developed for use in realization of mathematical operations such as addition, subtraction, multiplication (amplification), integration, and differentiation in analog computers. For this reason they are called operational amplifiers. Inverting and noninverting configurations are useful in the design of amplifiers, filters, and other signal conditioning applications.

1R

R

V

VA f

s

oinv

1

1R

R

V

VA f

s

ononinv

Inverting Non-inverting

0V

+

-

3V

2V

1V R

R

R

R

Ground

(a)

R

R

Inverting terminal

NonInverting terminal

1V

2V

(b)

oV

+

-

inV

oV

R

C

+

-

inV

oV

R

C

+

-

Ground

GroundGround

(c) (d)

_

+

_

+

_

+

_

+

)( 3210 VVVV

(a) An adder; (b) Subtractor; (c) Integrator; (d) Differentiator

dtVRC

V in

10

dt

dVRCV in0

120 VVV

inodV _

+

-

+

-

outodV _

-

+

(a) (b)

+

-

outocV _

-

+

inocV _

+

-

Open-loop common-mode configurationOpen-loop differential mode configuration

Differential amplifiers are characterized by a factor called the Common Mode Rejection Ratio (CMRR), which is the ratio of the open-loop differential gain , and open-loop common-mode gain , and is expresses in dB.

odA

ocA

oc

od

A

ACMRR 10log20

inod

outodod V

VA

_

_inoc

outococ V

VA

_

_

Gain

Lf

Frequency response curve of a high-pass filter

Frequency

Maximum gain

-3dB

Gain

Uf

Frequency response curve of a low-pass filter

Frequency

Maximum gain

-3dB

(a) (b)

The integrator and differentiator circuits are electronic filters because the circuits filter out some frequency components from the input signal.

(a) Gain versus. frequency response curve of a typical low-pass (integrator) filter;

(b) Gain vs. frequency response curve of a typical high-pass (differentiator) filter

UfLf

Maximum gainPower normalized to zero dB (100% power)

-3dB (50% power)

100% gain

71% hain

(a)

frequency

frequency frequency

UfLf


-3dB (50% power)

100% gain

71% hain

(b)frequency

UfLf


-3dB (50% power)

100% gain

71% hain

(c)

UfLf


-3dB (50% power)

100% gain

71% hain

(d)

Frequency response curve of various filters.

(a) Bandpass filter

(b) Band-reject filter

(c) Narrow-band filter (d) Notch filter

When the filters are designed using only passive elements such as capacitors and inductors, they are referred to as passive filters. A smoothing capacitor at the output of the rectifier circuit can be treated as a low-pass filter (Figure-6.5). Filters that are designed either using a transistor or OPAMP are called active filters.

A typical active bandpass filter using OP-AMP

Input CIRCUIT-1 Isolator CIRCUIT-2 Output

+

-

+

-

+

-

+

-

+

-

+

-

(a)

(b)

_

+Input

Output

Circuit-1 Circuit-2

Optoisolator

LED

Photodiode

(c)

Light

An isolator is a circuit that allows signals to be transferred between two circuits or systems, while keeping those circuits or systems electrically isolated from each other. The gain of the isolator or unity amplifier is unity. The isolation can also be achieved by utilizing optical signals. The electrical signal at the

output of the previous circuit is converted to light signal by a LED. Then the light signal is again converted to get back the electrical signal by using a photodiode or phototransistor.

-

+

-

+

-

+

1V

2V

oV

R R

RR

R

R

R

R

R Ground

+

-

Instrumentation amplifier is a kind of differential amplifier. It uses three OPAMPs. The third OPAMP behaves as an isolator. For high precision and high accuracy applications instrumentation amplifier are used. The configuration the open-loop differential gain is very high and the open-loop common-mode gain is small. It possesses high CMRR.

Excitation voltage

R1

R2

R3 R4+

-

Output

+

-

A

BC

D

Instrumentation Amplifier

+

-

Wheatstone bridge is a four-arm, four-terminal resistance-measuring electronic network. The bridge circuit is an important signal conditioning circuit, that can form the basis of capturing a very small fraction of change in the resistance value. The bridge is very reliable and is considered as a sophisticated and precision signal-conditioning circuit.

COMPARATORInput Output

+

-

+

-Comparator Input

Threshold or reference level

timeComparator Output

time

A typical sensor signal

+V volts

Comparators are employed in applications in which some sort of signal comparison is required. It is a circuit that typically contains a threshold or reference voltage level to which the voltage level of another signal is compared. If the signal to be compared is greater than the reference voltage setting then the comparator circuit provides an output in terms of a pulse or step signal.

-

+inV

oV

oV

inV

saturationV

saturationV

oV

inV

saturationV

saturationV

-

+

inV

oV

(a)

(b)

ccV

ccV

ccV

ccV

ccV

ccV

ccV

ccV

The two open-loop OPAMP circuits shown above can be used as comparators. The transition occurs based on whether the reference voltage (Vref = Vin ) is less than zero or greater than 0.

-

+

oV

ccV

ccV

+

-

refV

inV+

-

Figure shows a comparator circuit using an OPAMP in non-inverting mode. In the figure a reference source, which is equal to the threshold level, has been connected to the noninverting terminal. The signal to be compared with the reference voltage is applied to the inverting terminal. Whenever the input voltage is greater than the reference voltage the transition occurs, providing an output pulse or step.

Zero Crossing DetectorInput Output

+

-

+

-

ZCD Output

time

ZCD Input

time

time

ZCD Input

time

ZCD Output

Zero crossing detector (ZCD) is a kind of comparator that provides a signal (pulse or step) at the output when the input signal passes the zero level.

Amplitude Amplitude

Amplitude

AmplitudeAmplitude

Amplitude

time

time

time

time

time

time

(a) (b)

(c) (d)

(e) (f)

Signal conditioning circuits include waveform generators. Within automation and control, various types of oscillatory waveforms are required. The types of oscillatory waves are sinusoidal, triangular, impulsive, square- wave, saw-

tooth, staircase, and so on. Oscillators are electronic circuits that generate a oscillatory output voltage that repeats regularly at constant intervals.

Amplifier

Feedback circuit

A

B

All oscillator circuits are positive feedback systems.

Voltage divider

4R3R

2R

1R

2C

1C

Ground

oV

Lead-lag circuit

_

+

Depending upon the circuit configuration, different types of oscillators exist. They include the Wien-Bridge oscillator, phase-shift oscillator, Colpitts oscillator, Clapp oscillator, Hartley oscillator, and most versatile Crystal oscillators. Figure illustrates an OPAMP-based Wien-Bridge oscillator.

The lead-lag circuit provides a positive feedback.

RRR 34

CCC 21

RCfosc 2

1

If

then

3R

2R

1R

C

_

+

oV1V

saturationV

saturationV

oV

time

time

1V

lV

uV

Voltage across capacitor C

An OPAMP-based square-wave oscillator. The voltage across the capacitor is triangular in nature. If , then the frequency of oscillation is,

1V 23 86.0 RR

CRfosc

12

1

3R

2R

1R

CGround

_

+_

+

Ground

Comparator Integrator

oV

1V

saturationV

saturationV

1V

time

time

oV

lV

uV

The OPAMP-based triangular wave oscillator is shown in the figure. It uses two OPAMPs. The first OPAMP is a comparator and the second is an integrator. The voltage at the output of the first OPAMP is square-wave in nature. The integrator integrates the square-wave, producing a triangular wave.

3

2

14

1

R

R

CRfosc

Symbol

XTAL

R

L

C

0C

For getting stable and accurate oscillatory signal output, a piezoelectric quartz crystal is often used. The property of the quartz crystal is that when a changing mechanical stress is applied to the crystal, an oscillatory voltage is developed, whose frequency is the same as that of the mechanical stress vibrations. The highest vibration occurs at the natural frequency of the crystal. The frequency depends on dimensions, type of cut, thickness, temperature, etc.

There are many ways to design oscillator circuits. A basic oscillator circuit is available in IC form. NE555 or LM555, which are called timers that have the building blocks in one package. 555 IC are highly stable devices for generating relatively accurate oscillations.

-

+

-

+

R

R

R

Threshold

Control

Trigger

6

5

2

Comparator-1

Comparator-2

Flip-flop

Reset4

Output3

7Discharge

ccV

Ground

ccV3/2

ccV3/1

Transistor

1

(active low)

The internal basic building blocks of 555.

7

6

2

C

F01.0

aR

bR

3

5

1

Output

oV

555

)(tVc

ccV

A typical configuration of 555 by the use of external components for the generation of rectangular waves is shown in Figure. This type of configuration is called the free-running mode because the triggering signal is captivated from the timer. That is the trigger signal is generated from the 555 itself. The free-running mode of operation of 555 is called the astable mode. The time it stays high and the time it stays low are determined by the values of the external components.

CRRTf

CRRTTT

CRT

CRRT

ba

ba

b

ba

)2(

44.11

)2(693.0

693.0

)(693.0

21

2

1

ccV3/2ccV

ccV3/1

uV

time

time1T 2T

Output

Voltage waveforms across the output pin

Voltage waveforms across the capacitor

7

6

C

F01.0

aR

bR

3

5

1

Output

oV

555

)(tVc

ccV

2

Trigger signal

A monostable multivibrator circuit, on the other hand, has an output that stays in a given state (either low or high) until a separate signal triggers the timer. The trigger signals are provided externally. The monostable mode requires only two external components, and C. Time period is determined by

aR

CRT a1.1

+

-

inV

oscV+ -

+

-

D-1

D-2D-3

D-4

Ch

A

B

inV

outV

oscV

time

time

time

C D

1R

2R

Output+

- Vout

E

Sample and hold circuits (S/H) are very important in the context of analog to digital (AD) conversion of the signal. An S/H circuit is one that samples the analog signal at a particular instant and retains the value for a specified time for subseq-uent use.

Analog signal

Sampler Quantiser Binary Converter

Digital signal

Sample and hold

Analog signal

Quantised signalQuantisation level-15

Quantisation level-1

54321 SSSSS

54321 QQQQQ

Sampled signal

time

time

time

Amplitude

1110

0110

0110

1001

0110

5

4

3

2

1

Q

Q

Q

Q

Q

(a)

(b)

(c)

(d) Quanisation level-0

The analog to digital conversion (ADC) is achieved through three sub processes such as,

•Sampling•Quntisation•Coding

MultiplierPulsed signal

Analog signal in time domain

time

time

time

Analog signal in frequency domain

Multiplied signal in the frequency domain

sf sf2

USB-1 USB-2LSB-2LSB-1Signal


sf sf2



sf sf2


Ms ffCase :1

Mf frequency

frequency

frequency

frequency

Ms ffCase :2

Ms ffCase :2

Overlapping

Not overlapping

(b)

(a)

(c)

(d)

(e)

(f)

(g)

(h)

1

One of the important parameters of an ADC is the sampling frequency. There is a strict relationship between the sampling freq. and the signal freq. as far as exact recovery of the analog signal from the sampled signal is concerned. This relationship appears as the sampling theorem and states that "the sampling rate should be at least twice that of the highest frequency of the analog signal."

outV

dV

R 2R 4R 8R

16R32R

64R

128R

7

6

5

4

3

2

1

0

D

D

D

D

D

D

D

D0S

1S

2S

3S4S

5S

7S6S

fR

Ground

Data bits

0I 2I 3I 4I 5I 6I 7I2I-

+

Mainly two techniques are employed as far as Digital to Aanalog Conversion is concerned; binary resister-based and R-2R ladder-based D/A converters, respectively.

Binary resister-basedDAC

7

6

5

4

3

2

1

0

D

D

D

D

D

D

D

D

Data bits

0S 1S 2S 3S 4S 5S 7S6S

0I2I3I4I5I6I7I 2I

2R 2R 2R 2R 2R 2R 2R 2R 2R

Output

outI

256 mA R-2R ladder-based D/A converters

R

VI

R

VI

R

VI

R

VI

R

VI

R

VI

R

VI

R

VI

dddd

dddd

7654

3210

;2

;4

;8

16;

32;

64;

128

Digital to Analog Converter (D/A)

Counter

Input analog signal

Comparator

+

_

01234567 DDDDDDDD

00000000

00010000

00100000

00110000

01000000

01010000

01100000

01110000

10000000

10010000

10100000

10110000

11000000

11010000

11100000

11110000

00000001

00010001

00100001

00110001

01000001

01010001

01100001

01110001

10000001

Initial point

Counter output

Analog signal

Digital Equivalent

Only 24 levels out of 128 levels have been shown

Initial catching

Circuit diagram of a counter based A/D converter. There are three blocks; a comparator circuit that gives an output, i.e., a pulse when the inverting terminal exceeds the input analog signal, D/A converter converts digital signal to analog signal. The counter counts from zero to upward. The counter

based technique inherits initial catching problem.

Digital to Analog Converter (D/A)

Successive Approximation Register

Input analog signal

Comparator

+

_

01234567 DDDDDDDD

Buffer

MSB

LSB

pulse at the output, if the input signal is greater than the signal at the inverting terminal. The output is fed to a register, called buffer. The buffer is connected to another register called Successive Approximation Register (SAR). The output of the SAR is the digital equivalent of the analog input. The last block, as before is a digital to analog converter, whose input is from SAR and the output is connected to the inverting terminal of the comparator.

Successive approximation technique overcomes the initial catching problem. There are four blocks. The comparator, that produces a

N S

0

+_

Scale

Coil

Pointer

Input terminal

polepole

Galvanometer is an instrument that detects the presence, direction, and strength of an electrical current in a conductor. They operate on fundamental magnetic law that an electric current flowing through a wire in the presence of a magnetic field produces a force in the wire. Four basic components are integrated in order to observe the phenomenon, i.e., the flow of current. The components are a magnetic field, a coil, a pointer, and display.

Galvanometer Galvanometer

Ammeter Voltmeter

Ammeter connection

Ammeter

Circuit element

Voltmeter connection

Voltmeter

A B A

B

GalvanometerGalvanometer Galvanometer

Ammeter Voltmeter

Ammeter connection

AmmeterAmmeter

Circuit element

Voltmeter connection

Voltmeter

A B A

B

(a) (b)

(c) (d)

The galvanometer is used to measure small currents. To measure higher values some potentiometer type circuits are connected as heavy currents could damage the galvanometer. When the galvanometer is converted to measure the current it is called ammeter and when it is converted to measure the voltage it is called voltmeter.

(-) Cathode

+ + +

Intensity control grid

Focusing grid

Accelerating grid

Pair of Horizontal plates

Pair of vertical plates

Florescence screen

Electron beam

Cathode Ray Tube

The Cathode Ray Oscilloscope (CRO) is an equipment commonly used to measure and display signal parameters such as amplitude, frequency, and phase. A wide range of both AC and DC levels can be measured and displayed. The CROs are versatile, reliable, stable and can be handled easily. For these reasons, it is being used in many laboratories, research centers, and industrial sectors. CRT (Cathode Ray Tube) constitutes the main part of the CRO.

Cathode Ray Tube

Vertical plates

.Y=deflection

DC signal

.O

y2

Y=deflection

Vertical plates

DC signal inreverse direction

Wrt above

Peak deflection

Vertical plates

Sinusoidal signal

Vertical plates

.Y=deflection

DC signal

.Y=deflection

Vertical plates

Y=deflectionY=deflection

Vertical plates

DC signal inreverse direction

Wrt above

Peak deflection

Vertical plates

Sinusoidal signal

y1

O

y2

y1

HorizontalAxis

VerticalAxis The signal whose

parameters are to be measured and displayed is fed to the vertical plates. a linear saw-tooth signal called sweep signal is fed to the horizontal deflection plates for complete visualization. The frequency informa-tion of the signal can also be obtained.

Linear

Amplitude

Time

Sudden fall

A linear saw-tooth signal called sweep signal is applied across the horizontal deflection plates. Application of one cycle of the sweep signal, to the horizontal plates, causes the beam to be deflected across the screen. When the sweep signal suddenly falls to zero, the beam flies back to its initial position. Application of second cycle causes the beam to start deflecting in the horizontal direction again. However, because of the nature of the fluorescent screen and the other additional electronic circuitry, the fly-back part of the return trace of the beam cannot be seen. The sweep signal repeats, drawing the beam horizontally again and again in order to provide an illusion that the fluorescent point is not moving.

Vertical Amplifier

Trigger Generator

HorizontalAmplifier

Horizontal plate

Vertical plate

Screen

Sweep Generator

Input signal whose parameter is to be measuredA schematic block diagram of a typical CRO has been shown. The signal to be displayed is amplified by the vertical amplifier and applied to the vertical deflection plates of the CRT.

A portion of the signal in the vertical amplifier is applied to the trigger generator in order to provide triggering signal to the sweep generator. This pulse turns on the sweep generator, initiating the saw-tooth waveform. The saw-tooth wave is amplified by the horizontal amplifier and applied to the horizontal deflection plates.