signal integrity asif
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Signal Integrity
By Asif
Outline
Overview of SI
Transmission Line Theory
Time Domain Analysis
Frequency Domain Analysis
Equalization Techniques
High Speed interfaces
3D Modeling
Overview
Signal integrity is an important activity at all levels of
electronics packaging and assembly, from internal
connections of an integrated circuit (IC),through
the package, the printed circuit board (PCB),
the backplane.
SI is a set of measures of the quality of an electrical
signal.
That ensures all signals transmitted are received
correctly.
That ensures signals don’t interfere with one another.
That ensures signal don’t damage any device.
Transmission line Theory
Introduction
Lossy Transmission Line
Lossless Transmission Line
Single Ended Signaling
Differential Signaling
Tightly Coupled & Loosely Coupled
Introduction
The transfer of energy from one point to another takes
through either wave guides or transmission lines.
In an electronic system, the delivery of power
requires the connection of two wires between the
source and the load. At low frequencies, power is
considered to be delivered to the load through the
wire.
In the microwave frequency region, power is
considered to be in electric and magnetic fields that
are guided from lace to place by some physical
structure. Any physical structure that will guide an
electromagnetic wave place to place is called a
Transmission Line.
Lossy Transmission Line
Impedance of lossy Transmission line is,
Where R-series resistor of the conductor
L-due to the magnetic fields self inductance
C-shunt capacitor between two conductor
G-shunt resistor between signal wire and the return wire
Z0-charecteristic impedance
Lossless Transmission Line
Impedance of lossless Transmission line is,
When the R and G are negligibly small the
transmission line,the model depends only on the L
and C elements
Single Ended Signaling
A single-ended measurement is taken as the voltage
difference between a wire and ground.
The noise is only on the positive wire, and as a
result, it is still measured along with the output
voltage from the sensor
Single-ended signaling is the simplest and most
commonly used method of transmitting electrical
signals over wires.
One wire carries a varying volt that represents the
signal, while the other wire is connected to a
reference voltage, usually gnd.
Differential Signaling
Differential signal is a method of transmitting
electrically with two complementary signal sent on
two pared wires called differential pair
It is Suitability for use with low-voltage electronic
signals.
It will resist the EM interferences.
The main benefit of a differential measurement is
noise rejection
Tight coupling &Loosely coupled
Tight coupling is usually reduces flexibility and re-usability A Tightly
Coupled Object is an object that needs to know quite a bit about
other objects and are usually highly dependent on each other's
interfaces.
Loosely coupled to reduce the inter-dependencies between
components of a system Loose coupling is a much more generic
concept intended to increase the flexibility of a system
Difference between Time& Frequency
Domain Analysis
Time domain analysis examines the amplitude vstime characteristics of a measuring signal
Time domain analysis gives the behavior of the signal over time
Frequency domain analysis replaces the measured signal with a group of sinusoids which, when added together, produce the waveform equivalent to original
The relative amplitudes, frequency, phases of the sine waves are examined
Frequency domain analysis is much easier, some equations are can’t be solved while time domain they can be solve easily in frequency domain
Difference between Time& Frequency Domain
Analysis
Time Domain Analysis
Introduction
Eye pattern
Jitter
Setup/Hold Time
Rise Time/Fall Time
Introduction
A graphical representation of the change of some
value with respect to time
In the time domain, the signal or function's value is
known for all real numbers, for the case
of continuous time, or at various separate instants in
the case of discrete time
A time-domain graph shows how a signal changes
with time, whereas a frequency-domain graph shows
how much of the signal lies within each given
frequency band over a range of frequencies.
Eye Pattern Evoluation of combined effect of channel noise and Intersymbol
interference(ISI).
Open eye pattern corresponds to minimum signal distortion.
Jitter
• Jitter is the deviation from true periodicity of a presumed
periodic signal in electronics.
• Jitter period is the interval between two times of
maximum effect (or Minimum effect) of a signal that
varies with time.
1.Ranfom Jitter(gaussian Jitter)
• Is unpredictable electronic noise
• Random jitter typically follows a gaussian distribution or
normal distribution
• Caused by thermal noise and another reason for jitter to
have a distribution or normal distribition
Jitter(Cont…)
2.Deterministric Jitter
It is a type of clock timing jitter or data signal jitter is
predictable and reproducible
The peak to peak value of this jitter is bounded and
the bounds can easily be observed and predicted
Total jitter
Total jitter (T) is the combination of random jitter (R)
and
deterministic jitter (D)
T = Dpeak-to-peak + 2× n×Rrms,
in which the value of n is based on the bit error rate
(BER) required of the link
Setup Time Setup time is the minimum amount of time the data signal should be
held steady before the clock event , so that the data are reliably
sampled by the clock.This applies to synchronous circuit such as flip
flop.
The time when input is available and stable before the clock pulse is
applied is called setup time.
Hold Time Hold time is the minimum amount of time the data signal should be
held steady after the clock event, so that the data are rapidly
sampled.
The time after clock pulse where data input is held stable is called
hold time.
Rise Time/Fall Time
Rise Time(TR)
Amount of time it takes the output voltage to go from 10%
of the Logic "1" level to 90% of the Logic "1" level..
Measured in nS.
Fall Time(TF)
The time required for the output voltage to go from 90%
of the Logic "1" level to 10% of the Logic "1" level..
Measured in nS.
Frequency Domain Analysis
Introduction
S-Parameter
Insertion Loss
Return Loss
Cross Talk
Nyquist Frequency
Knee Frequency
Skew
Introduction
The frequency response of a system is defined
steady state response of the system
A graphical representation of the amount of energy
present in a signal at each of many frequencies
The frequency response of a system is defined
steady state response of the system
The frequency domain values are really just a series
of sinusoidal equivalents, so amplitudes are usually
represented the same as in the time domain.
The frequency domain is usually derived by
computing a Fast Fourier Transform (FFT) of a time
domain signal.
S-Parameter
S-Scattering parameters which describe electrical behavior of
transmission line signals.
The following information must be defined when specifying a set of
S-parameters:
• The Frequency(f)
• Characteristic impedance (Z0)
• Number of Ports
Use it as a simplified passive interconnect model that
– simulates faster,
– is easier to correlate with actual hardware, and
– can be offered to the industry while protecting IP
S-Parameter(cont…)
A behavioral representation (model) of passive
interconnect
Insertion Loss
The loss of signal power resulting from the insertion
of a device in a transmission line
Is usually expressed in db
PT is power transmitted
PR is power received
Return Loss
The loss of power in the signal returned/ reflected by
a transmission line
This discontinuity can be terminating load or with a
device Inserted in the line
Pi incident power
Pr reflected power
Cross Talk(XT)
crosstalk (XT) is any phenomenon by which
a signal transmitted on one circuit or channel of
a transmission system creates an undesired
effect in another circuit or channel.
Crosstalk (cont….)
Cross Talk occurs on PCB and twisted wire cable
Crosstalk (cont….)
Near end crosstalk(NEXT)
NEXT is a measure of the ability of the cabling to reject crosstalk
The signals traveling through adjacent pairs of wire in twisted pair
cabling interfere with each other
Interference between two pairs in a cable is measured at the same
as the interfering transmitter
Power Sum Near end Crosstalk(PSNEXT)
A NEXT measurement which includes the sum of crosstalk
contribution of all adjacent pairs
Far end Crosstalk(FEXT)
Interference between two pairs of a cable measured at the other end
of the cable with respect to Interfering transmitter
Crosstalk (cont….)
Equal Level Far end Crosstalk(ELEFEXT)
An FEXT measured with attenuation compensation.
Power Sum Far end Crosstalk(PSFEXT)
It is the sum of all interference signals, which are
coupled in a pair of conductors.
Nyquist Rate
Minimum sampling rate required to prevent alaiasing
Defines the maximum sampling rate given a fixed
maximum frequency
The maximum frequency that won’t be alaised, is “half”
the given sampling rate.
fs≥2fc
Fs- Sampling Frequency fc- Highest Frequency
Nyquist Rate(cont…)
Alaiasing
The sampling points are correct but produce a
completely different wave
Knee Frequency
Knee frequency is an estimate of the highest frequency content of the signal
If the Rise Time is smaller the highest frequency content will have higher frequency
If ‘t’ denotes the 10% to 90% rise time of a signal,then an estimate for the highest frequency content of the signal(or)Knee Frequency given by
fmax Highest Frequency content
Skew
Skew is the time delta between the actual and expected arrival time
of a clock signal.
The time delay difference between two or more signal path is called
skew
It can be intrinsic or Extrinsic
Intrinsic: Propagation delay between the device outputs.
Extrinsic:Due to unbalanced trace lenghts (or) output loading.
High Speed Interfaces
DDR(Double Data Rate)
SAS(Serial Attached SCSI)
SATA(Serial Advanced Technology Attachment)
USB(Universal Serial Bus)
PCIE(Peripheral Component Interconnect Express)
DDR(Double Data Rate)
DDR SDRAM is a class of memory integrated circuits used in computers.
DDR SDRAM, also called DDR1 SDRAM, has been superseded by DDR2 SDRAM and DDR3 SDRAM.
Compared to single data rate (SDR) SDRAM, the DDR SDRAM interface makes higher transfer rates possible by more strict control of the timing of the electrical data and clock signals.
DDR SDRAM with a certain clock frequency achieves nearly twice the bandwidth of a SDR SDRAM running at the same clock frequency.
DDR SDRAM gives a transfer rate of (memory bus clock rate) × 2 (for dual rate) × 64 (number of bits transferred) / 8 (number of bits/byte). Thus, with a bus frequency of 100 MHz, DDR SDRAM gives a maximum transfer rate of 1600 MB/s.
DDR(cont…) VERSIONS
• SDRAM-66 MHz,100 MHz,133 MHz
• DDR1-266,333,400 MHz
• DDR2-400,533,677,800 MHz
• DDR3-460,533,677,800,933,1066 MHz
• DDR4-1600 to 3200 MHz
LRDIMM
DIMM-Dual Inline Memory Module, comprises a series of
dynamic random-access memory integrated circuits
LRDIMM-Load Reduced DIMM,this technology uses
distributed buffer approach to accomplish memory
bandwidth efficiency
Improve LRDIMM architecture for better SI or data
signals
That support higher densities than RDIMM and contain
memory buffer
LRDIMM uses in memory intensive application in data
centers ,could computing and high performance
computing(HPC) environments
RDIMM
RDIMM-Registered Dual In line Memory Module
This is in constrast to the unbuffered data approach used
with DDR4
DDR4 LRDIMM’s shorter trace length and quicker
buffering scheme make the overall latency and bus
read/write turnaround time compared to DDR4 RDIMM
UDIMM
UDIMM-Unbuffered/Unregistered DIMM
When compared to registered
memory(RDIMM),conventional memory is usually
referred as UDIMM
Most commonly in PC and Laptops
It’s faster than the RDIMM and low cost. But are not
stable as RDIMM
SAS(Serial Attached SCSI)
SCSI-Small Computer System Interface
When it was introduce the speed of SAS is 3Gbps,Then In 2009 the
speed of SAS is 6Gbps,In 2013 speed is increased to 12Gbps
It is point to point serial protocol that moves data to and from
computer storage devices
Types of component,
• Initiator-Request for processing by a target devices
• Target-Contains logical units and target ports
• Service Delivery Subsystem-I/O system transmit initiator to
target and vice versa
• Expanders-Communicate between multiple SAS devices to
initiator port
SATA(Serial Advanced Technology
Attachment)
SATA is the next generation storage interface for
PCs and low-end Servers.
SATA is highly viable for servers and storage
networks
One SATA controller can aggregate multiple ports
Multiple SATA drives can be linked using backplanes
and external enclosures
SATA was designed to provide excellent speed and
storage at a low cost
Cost and scalability provides potential for greater
storage capacity at a lower cost than networked or
server storage
SATA(cont…)
SATA revision 1.0 - 1.5 Gbit/s - 150 MB/s
SATA revision 2.0 - 3 Gbit/s - 300 MB/s
SATA revision 3.0 - 6 Gbit/s - 600 MB/s
SATA revision 3.1
SATA revision 3.2 - 16 Gbit/s - 1969 MB/s
PCIe(Peripheral Component Interconnect
Express)
PCIe is a high speed serial computer expansion bus.
A computer bus is used to transfer data from one location
or device on the motherboard to the central processing
unit where all calculations take place.
PCIe has been a versatile ,function way to sonnect
sound,video and network card to a mother board.
Two different parts of a Bus
Address bus-transfers information about where the
data should go
Data bus-transfers the actual data
PCIe(cont…)
Plug&Play(PnP)
Automatically recognized and configured to work on
the system.
PCIe(cont…)
Every device has its own dedicated connection,so
devices no longer share bandwidth like they do on a
normal bus.
PCI Express link performance
USB
USB-Universal Serial Bus
Nowadays most of the electronic devices are connected by the USB
USB needs to operate at maximum voltage of 5.00 V and maximum
current of 500-900 mA
USB has can connect maximum number of devices around 127
It is a 4 pin connector
• Pin 1-Vcc(+5V)
• Pin 2-(D-)
• Pin 3-(D+)
• Pin 4-Gnd
USB(Cont…)
VERSIONS,• USB 0.7 – released in November 1994
• USB 0.8 – released in December 1994
• USB 0.9 – released in April 1995
• USB 0.99 – released in August 1995
• USB 1.0 - Release Candidate – released in November 1995
• USB 1.x -12 Mbps
• USB 2.0 -480 Mbps
• USB 3.0 -3.2 Gbps
• USB 3.1 -10 Gbps
Equalization Techniques
Emphasis
FFT
IFFT
FFE
DFE
CTLE
FIR
FFE
Emphasis
Emphasis is the intentional alteration of the amplitude-vs
-frequency characteristics of the signal to reduce the
effects of noise in a communication
Pre-emphasis:
Pre-emphasis refers to boosting the relative amplitudes
of the modulating voltage for higher audio frequencies
from 2 to approximately 15 KHz.
Which boosting the relative amplitudes for high frequency
to improve the overall signal to noise ratio and the mirror
operation is called de-emphasis
pre-emphasis is done at the transmitter
Emphasis(cont…)
De-emphasis:
De-emphasis is the complement of pre-emphasis.
De-emphasis means attenuating those frequencies by the amount by
which they are boosted.
de-emphasis is done in the receiver.
The whole system of pre-emphasis and de-emphasis is called
emphasis
FFT
Fast Fourier Transform (FFT) is to compute
the discrete Fourier transform (DFT) and its
inverse. Fourier analysis converts time (or space) to
frequency and vice versa
The DFT is most important in the area of frequency
(spectrum) analysis because it takes a discrete signal in
the time domain and transforms that signal into its
discrete frequency domain representation
The most important difference is that an FFT is much
faster than DFT
FFT algorithms are also much more accurate than
evaluating the DFT
IFFT
The Fourier transform is used to convert the signals from time domain to frequency domain and the Inverse Fourier transform(IFFT) is used to convert the signal back from the frequency domain to the time domain
FFT which is a technique to analyse signal in frequency domain. If signal is in time domain and are not able to find problem then we can take FFT of this signal and find out how many frequency components are present and analyse it better
if we convert it back to time domain then all frequency will be available but it will be difficult as which frequency was present at what time, so one can replace IFFT and FFT
FFE
Feed-Forward Equalization (FFE) is an equalization
technique that corrects the received waveform with
information about the waveform itself and not information
about the logical decisions made on the waveform
FFE basically acts like a FIR (finite impulse response)
filter and uses the voltage levels of the received
waveform associated with previous and current bits to
correct the voltage level of the current bit
FFE is only concerned with correcting voltage levels in
the waveform
The mathematical expression of FFE is,
e(t) = c0r(t - (0TD)) + c1r(t - (1TD)) + c2r(t - (2TD))
DFE
Decision Feedback Equalization (DFE), DFE
calculates a correction value that is added to the
logical decision threshold
The mathematical expression of FFE is,
V(k) = c1s(k - 1) + c2(k - 2)
DFE and FFE are different equalization techniques,
it is not uncommon to use both at the receiver
DFE and FFE are both useful equalization
techniques that can be used to open closed eyes at
the receiver
CTLE
CTLE- Continous Time Linear Equalization
In the transmitter, equalization using a CTLE is
implemented to provide pre-emphasis of the high
frequency leading edge of bit transitions
This can be done in two techniques are,
1) CTLE using high pass filter (HPF) with poles and
zeros
• A HPF CTLE can provide emphasis in its high
frequency response and can be created using a
single pole and zero, H(s) = K*(s-z)/(s-p)
2)CTLE using a feed-forward equalizer (FFE)
• A FFE CTLE can provide emphasis in its high
frequency response and be created using
delays,gains and summer
FIR
Finite impulse response (FIR) filter is
a filter whose impulse response (or response to any
finite length input) is of finite duration, because it
settles to zero in finite time
This is in contrast to infinite impulse response (IIR)
filters, which may have internal feedback and may
continue to respond indefinitely
For a discrete-time FIR filter of order N,
3D Modeling
Introduction
MOM-Method Of Moments(2D)
Quasi Static Modeling(2.5D)
FEM-Finite Element Modeling(3D)
FDTD-Finite Difference Time Domain(3D)
Introduction
Advantages of Simulation Modeling are,
• Optimize the geometry for strength and weight
• Select materials that meet weight, strength, and budget
requirements
• Simulate part failure and identify the loading conditions
that cause them
MOM
MOM-Method Of Moments
Analyzing PCB with respect to radiated emission and
radiated susceptibility in the frequency domain
Can be used for analyzing any planar structure
EMC applications-Electro magnetic
compatability,shall not generate EM disturbance
Quasi Static Modeling(2.5D)
FDTD-Finite Difference Time Domain Method
Numerical Analysis technique
FDTD can cover wide range frequency with a signal
simulation
It will used in a non linear material property
FDTD uses the E and H fields directly. Since most
EMI/EMC modelling applications are interested in
the E and H fields
FEM
FEM-Finite Element Modelling
It is a numerical technique for finding approximate
solutions to boundary value problems for partial
differential equations
It uses subdivision of a whole problem domain into
simpler parts, called finite elements
from the calculations of variations to solve the
problem by minimizing an associated error function
It will solve electro magnetic field(TE,TM,TEM)
FDTD
FDTD-Finite Difference Time Domain Method
Numerical Analysis technique
FDTD can cover wide range frequency with a signal
simulation
It will used in a non linear material property
FDTD uses the E and H fields directly. Since most
EMI/EMC modelling applications are interested in
the E and H fields
DESIGN OF EXPERIMENTS
It is a design of any information gathering exercise
where variation is present
These statics used for controlled experiments
Advantages of DOE,• Reliability is increased
• Shorter development time
• Process performing normal
• Cost is less
• Reduction of process variation
GENETIC ALGORITHM
Genetic algorithm(GA) is a heuristic that mimics the
process of natural selection
Heuristic is designed for solving problem more
quickly
GA which generates solution to optimization problem
using techniques inspired by natural evolution
ARTIFICIAL NEURAL NETWORK(ANN)
An Artificial Neural Network (ANN), usually called neural
network (NN), is a mathematical model or computational
model that is inspired by the structure and/or functional
aspects of biological neural networks
A neural network consists of an interconnected group
of artificial neurons, and it processes information using
a connectionist approach to computation
HFSS-High Frequency Structural Simulator
Solution Types:
Driven Modal: Use this type of solution for passive high frequency
structures such as microstrips, waveguides, and transmission lines.
Driven Terminal: Use this type for simulations that deal with
signal integrity for models that have multi-conductor transmission lines.
Eigenmode: Use this type to calculate resonances of a given
structure(e.g. filters).
Transient: Use this type to employ time-domain solutions for
simulations with pulsed excitations such as ultra-wide band antennas.
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