Introduction to the Design and Development of Mixed Signal

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Introduction to the Design and Development of Mixed Signal
Introduction to the Design and Development of
Mixed Signal Integrated Circuits
Tutorial 2
Prashant Bhadri
Raghuram Srinivasan
Sunday, August 7, 2005
15:30-18:30 pm
IEEE International 45th Mid-West Symposium
on Circuits and Systems
Cincinnati, Ohio
Copyright Information
This presentation is an “Open Access” material and therefore
please credit the presenters if you reproduce any of this information
Presenter’s Information
Education
z B.S. in Electronics and Communication
z M.S. in Electrical Engineering
z Post-Doctoral Fellow at the Doheny Eye
Institute, Keck’s School of Medicine
University of Southern California, Los Angeles
Research Focus
z Engineering Solutions in Medical Domain
z Analog, Digital, Mixed Signal Circuit Design,
Testing and Analysis
z Field Programmable Gate Arrays
z Product Development of Medical Devices
Prashant R Bhadri
Doctoral Researcher
University of Cincinnati
Academic Achievements
z 30 papers presented and published in journals,
conferences, and magazines
z 2 provisional patents
z Recipient of Rindsberg Fellowship
z Recipient of SPIE Travel Award
Education
z B.S. in Electrical Engineering
z M.S. in Computer Engineering
Research Focus
z Improving Simulation Time using MultiThreading in a Frequency Extended VHDL-AMS
z Analog, Digital, Mixed signal Circuit Design,
Testing and Analysis
z Formal Verification Methods to Analog and
Mixed-Signal Systems
Raghuram Srinivasan
Doctoral Researcher
University of Cincinnati
Information
Prashant R. Bhadri
Raghuram Srinivasan
Department of ECECS, College of
Department of ECECS, College of
Engineering, University of Cincinnati,
Engineering, University of Cincinnati,
PO Box-210030,Cincinnati, Ohio - 45221
PO Box-210030,Cincinnati, Ohio - 45221
Fax – (513)556-7326
Fax – (513)556-7326
Email: [email protected]
Email: [email protected]
Copy of the material available on:
Distributed Processing Laboratory: www.ececs.uc.edu/~dpl
Dr. Fred R. Beyette Homepage: www.ececs.uc.edu/~beyette
Outline of the Tutorial
Motivation
Overview
Detailed Design Process
Simulation with VHDL-AMS
Evaluation Process
Conclusions
Acknowledgements
Question and Answers
Motivation
Major need for mixed-signal chips driven by consumer products
Cell phones
Music players
Digital Cameras
As frequency increases, digital circuits become more analog
Clock distribution (PLL’s, pulse shapers, oscillators)
Pad design (buffers, protection circuits)
Interconnect (become more like transmission lines)
Logic cells (become more like RF and microwave circuits)
When Digital becomes Analog?
Issues in Mixed-Circuit Design
As feature size decreases, RF circuit issues become dominant in both
digital and analog circuits
Noise
Coupling noise
Component noise
Power supply and ground noise
Circuit parameters
Impedance mismatches
Gain
Major need for analysis methods and tools
Status of Mixed-Signal Design
Current technology supports mixed-signal circuits on a chip
Bi-CMOS
CMOS extended with analog insulator layer
Design tools just coming online
Analog and Mixed-Signal (AMS) modeling and simulation
AMS synthesis (still in research stage)
Comparison of CMOS, Bipolar and Bi-CMOS
Reference: R.J. Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition, John Wiley and Sons, 2005
Common Applications of Bi-CMOS
Bi-CMOS circuits are used in places where devices with significant drive
current can be used to significantly enhance system performance
Many microprocessor designs utilize BiCMOS circuits in their bus
controllers, floating point processing unit and the processor core where
speed is critical
Circuits where power consumption is a concern (ex. Cache Memory) are
implemented in the less power hungry CMOS circuits
Reference: R.J. Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition, John Wiley and Sons, 2005
Outline of the Tutorial
Motivation
Overview
Detailed Design Process
Simulation with VHDL-AMS
Evaluation Process
Conclusions
Acknowledgements
Question and Answers
M-S Design Flow
SPECIFICATION
DESIGN
TESTING
VERIFICATION
FABRICATION
Component Flow
Specifications
Functional Descriptions, Algorithms
+
Functional
Design
Architecture
Circuit
Floorplan
Physical
Design
-
Blocks
Abstraction
Reference: Ken Kundert, Henry Chang, Dan Jeffries, Gilles Lamant, Enrico Malavasi, Fred Sendig, "Design of
Mixed-Signal Systems-on-a-Chip", IEEE Trans. on CAD of ICs and Systems, Vol.19, No. 12, pp. 1561-1571,
December 2000.
System Domain
Integrated circuit design:
Complex activity
Well-defined process
The system is divided into
functional blocks (subsystems)
Defined first with respect to their
interfaces between each other
A series of design steps each
follow modeling the results
Simulation of the model assures
the design meets the requirements
Iterative Design Process
Hardware System
Design Flow
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
M-S Design vs. Digital Design
Components – Analog/Digital
Design Input – Behavioral/Structural
Verification – VHDL/Spice/VHDL-AMS
Synthesis – Analog is time consuming
Fabrication & Testing – Separate steps for Analog and
Digital Components
Flow Description
Results
Specifications
Layout Design
Verification Design
System Design
Courtesy: Dr. Harold Carter
Circuit Design
Novel Issues in M-S Design
Specification – Too many decision parameters
Design – Diverse fields of specializations required
Verification – Analysis of multiple domains
Evaluation – Statistical analysis
Fabrication – SOC fabrication
Outline of the Tutorial
Motivation
Overview
Detailed Design Process
Simulation with VHDL-AMS
Evaluation Process
Conclusions
Acknowledgements
Question and Answers
Definitions
A set of requirements that need to be satisfied
Requirements of a “Good” Specification:
Unambiguous
Avoid contradictions
Realizable with current technology capabilities
Specification Parameters
Functional parameters - Throughput
Analog parameters – Bandwidth, Gain, Threshold etc.
Design parameters – Area, Power, etc.
Types of components available
Environment – Temperature, Pressure etc.
Industry Standards provides the base specification
Advantages of Clear Specification
Quicker design cycle due to fewer errors
Testing of components from respective specifications:
ex: Virtuoso Aptivia Specification-driven environment
Driving Design Cycles – HDL Models are capable of:
Being subjected to behavioral analysis (simulation)
Layout generation (ASIC, FPGA)
Examples of Specification Tools
Statecharts/Automata
Formal
Specification
HDL’s: ObjectiveVHDL, SystemVerilog, HDL Monitors,
OpenVera, Rosetta
Software: SpecC, SystemC, Java
Behavioral Models: VHDL-AMS/ VHDL/ Matlab
Challenges in a M-S Environment
Increased design parameters, increases constraints
Multiple levels/domains of specification
Constant updates due to technology advances
System Specification
In a product development environment, the specification document presents
the first set of guidelines for an initial design of the system that would solve a
given problem
System specifications contain explicit details of the design:
Size
Speed
Power
Cost
Functionality
Constraints on available resources need to be taken into account before
developing these for the system and the specification in turn imposes
constraints on the design process
Most standard designs detailed data sheets are available to design engineers
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
System Design
Translation of the “Specs” into a micro-electronic circuit
Before Beginning:
Top Down / Bottom Up
Level of Abstraction
Type of Final Design – SOC/MS/Analog/Digital
Availability of Resources
Example M-S System
Reference: http://www.techonline.com/community/tech_topic/bluetooth/33005
M-S Design Process
Review Specification
Design Control Circuitry
Replace blocks in design with circuit components
Check if IP/Parameterized models are available
Power/Layout/Area aware design
Characteristics of a “Good” Design
Tradeoff between analog and digital components
Reduced layout complexity
Post-fab testability
Flexibility in design modifications:
Corrections
Posterity
Challenges in M-S Design
Full custom design vs. IP reuse
Multiple domains make controller design more complex
Optimization choices much fewer
Stricter Design Rules
System Design
Use of Hardware Description Languages (HDL’s) for describing a system in
the Register Transfer Level (also called RTL)
Higher levels of abstraction (e.g., behavioral level) are employed for larger
designs; lower levels (e.g., gate level, transistor level) for smaller designs
This shift from purely digital to Mixed-Signal (MS) systems has risen due
to the high values of operating frequencies in communication circuits and
shrinking feature sizes
Design productivity is one of the major issues of concern in VLSI systems
With the size of the chip decreasing exponentially, the complexity of the
gates has been increasing exponentially but design methodologies have not
kept up with the circuit complexity
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Design Hierarchy
Bread Board
Printed Circuit Board
SMT
ASIC
Block Level Implementation
Lakshminarayanan Ramasamy, “ ASIC System Development of MEMS Bio-Chip Analyzer
with Calibration, Signal Capture and Display Circuit”, Masters Thesis, March 2005
PCB & SMT Implementation
Lakshminarayanan Ramasamy, “ ASIC System Development of MEMS Bio-Chip Analyzer
with Calibration, Signal Capture and Display Circuit”, Masters Thesis, March 2005
M-S Design
Photoreceiver Flow Diagram*
Photocurrent is generated that is amplified and processed
Conversion of the signal from analog to digital with standard CMOS digital
circuitry or use the analog signal directly to the next stage of the circuitry
Various implementations of photoreceiver circuits is presented where the front end
is an optical detector followed by amplifier and processing.
*Prashant Bhadri et.al.,“Design and implementation of CMOS photoreceivers”, Proc. SPIE:
Optical Information Systems II, October 2004, Vol. 5557, p. 173-184
Optical Detector Configurations
CMOS Photodetector*
Response to optical illumination in the visible to IR wavelength range
Photodetectors fabricated through the MOSIS foundry service
Types of photodetectors are:
P-diffusion to N-well
N-well to P-substrate
Combination
Bipolar Junction Phototransistor
Reference: Prashant Bhadri et. al, “Implementation of CMOS photodetectors in optoelectronic circuits” Proc. IEEE:
Lasers and Electro-Optics Society, The 15th Annual Meeting of the IEEE, November 2002, Vol. 2, p. 683 - 684
ASIC Circuit
User threshold programmable photoreceiver that monolithically integrates at chip
level with the Multi Technology-FPGA
User programmed with the receiver threshold set to one of eight sensitivity levels
The output from the photoreceiver cell can be stored in SRAM cells
By decoding three programming bits (IN0, IN1, IN2) 8 different threshold levels
can be established and hence the user can program the sensitivity of the receiver
*Prashant Bhadri et.al.,“Design and implementation of CMOS photoreceivers”, Proc. SPIE:
Optical Information Systems II, October 2004, Vol. 5557, p. 173-184
Layout Level
Transimpedance Amp.
Differential
Amp.
Threshold
generation
Metal
Shielding
Guard
Rings
N-well/p-substrate
photo-diode
Reference: Prosenjit Mal et.al.,“Development of a Multi-technology FPGA: A Reconfigurable Architecture for
Photonic Information Processing” Proc. SPIE: Emerging Optoelectronic Applications, June 2004, Vol. 5363, p. 27-38
System Layout
Reference: Prosenjit Mal et.al.,“Development of a Multi-technology FPGA: A Reconfigurable Architecture for
Photonic Information Processing” Proc. SPIE: Emerging Optoelectronic Applications, June 2004, Vol. 5363, p. 27-38
Summary
Top Level FPGA Design
MTFPGA Chip Layout
Commercial FPGA devices are electronic
Need for incorporation of nontraditional multi
technologies into CMOS VLSI systems
Proposed a novel architecture that extends the
flexibility, rapid prototyping and reusability
benefits associated with conventional
electronics into the multi-technology domain
MTB Floor Plan
Reference: Prosenjit Mal et.al.,“Development of a Multi-technology FPGA: A Reconfigurable Architecture for
Photonic Information Processing” Proc. SPIE: Emerging Optoelectronic Applications, June 2004, Vol. 5363, p. 27-38
Circuit Design
The circuits are designed as cell libraries and then simulated using one of
many available circuit simulators
These designs are close to the required specification values as a general idea is
obtained during this step
The challenges are in the form of shrinking chip design requirements, pushing
the power and performance boundaries and the need to integrate most of the
applications
Due to the gradual evolution of the semiconductor process technology, new
types of circuit architecture are being implemented
As many of the innovative applications assume very low-cost implementations
of circuit building blocks, low-cost technology such as CMOS
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Gate Layout
Layout can be very time consuming
Design gates to fit together nicely
Build a library of standard cells
Standard cell design methodology
VDD and GND should abut (standard height)
Adjacent gates should satisfy design rules
NMOS at bottom and PMOS at top
All gates include well and substrate contacts
Other Issues
Noise
Power
Delay
Chip Noise
Circuit noise includes all the disturbances by the circuit’s topology
Interconnect noise includes noise coming from capacitive or inductive
coupling between interconnects
Power supply noise, which refers to deviations of the supply and
ground voltages from their nominal values
Substrate noise in mixed-signal integrated circuits:
For Example:
The charge injected in the substrate by the logic gates during
the transitions may interfere severely with the operation of
sensitive analog circuits
Reference: Bartolo’s Thesis, Chapter 1
Shot Noise
In a transistor the major contributor to noise is called shot noise.
The formula for shot noise in a diode is given as:
Reference: Lowen, S.B et.al,“ Power-law shot noise”, Information Theory, IEEE Transactions on
Volume 36, Issue 6, Nov. 1990 Page(s):1302 - 1318
Thermal Noise
The noise generated by the agitation and interaction of electrons is called
thermal noise. The internal kinetic energy of a particle can be expressed
through its temperature.
The kinetic energy of a body is zero at a temperature of absolute zero.
The noise generated by a resistor, for example, is proportional to its absolute
temperature as well as the bandwidth over which the noise is to be measured.
Reference: Bing Wang,et.al; “MOSFET thermal noise modeling for analog integrated circuits”, Solid-State Circuits,
IEEE Journal of Volume 29, Issue 7, July 1994 Page(s):833 - 835 ue 6, Nov. 1990 Page(s):1302 - 1318
Charge Injection
Problem
Solution
When the switch is on, the voltage across the sampling capacitor tracks the timevarying input signal within the bandwidth.
Some charges are present in the MOS channel, this is a result of forming a
conducting channel under the MOS gate.
When the switch is turned off, charges either flow to the input source or to the
sampling capacitor and create a small voltage which . is a function of several
parameters which include input impedance, source impedance, clock falling edge.
Reference: http://kabuki.eecs.berkeley.edu/~gchien/thesis/Masters/appB/appendixB.pdf
Clock Feed-through
When the clock voltage on the gate switches between high and low, this voltage.
drop is coupled into the signal via the capacitor divider.
The clock feed-through can be corrected to the first order by using a differential
signal path.
As long as the error is present on both signal inputs and the same magnitude, it can
be cancelled by taking the input differentially.
This technique, once again, depends on the absolute matching of transistors.
Reference: http://kabuki.eecs.berkeley.edu/~gchien/thesis/Masters/appB/appendixB.pdf
Ground Bounce
For significant flows the voltage drop across this inductor is given by:
VB = L dI/dt
For a 50 mA current change over 3 ns in a 3mm x 1 cm line
VB = 50 mV which is enough “noise” to disrupt digital signal quality.
Reference: http://klabs.org/richcontent/Tutorial/new_modules/ground_bounce.pdf
Latch-up
This spiking problem leads to a condition called latch-up
Falling edge spike goes through C2 turning on transistor Q2
Current flow through Q2 causes voltage drop across RW1 and RW2 turning on transistor Q1
Current flow through Q1 causes voltage drop across RS1 and RS2 further turning on Q2
Rising edge spike has same effect starting with pass through C1
Reference: R.J. Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition, John Wiley and Sons, 2005
Solutions to Latch-up
Slow the rise/fall time to reduce the size of the spikes
Reduce the size of drain region to reduce C1 and C2.
Reduce RW1 and RS2 by placing substrate and well
contacts close to the transistor drains
Place n+ and p+ regions around critical circuits. These
features (called guard rings) are effective but take
space and limit the ability to use poly as an
interconnect layer
Reference: R.J. Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition, John Wiley and Sons, 2005
Layout Design
It is very important for a layout designer to understand the bounds of laying
out a circuit as it depends on the type of the circuit designed
This step characterizes a chip as a whole where a circuit is laid out, then
extracted and its functionality checked
During the extraction process a large number of parasitic including
capacitances, inductances and resistances is obtained that lead to more
complications in circuit design
Therefore one of the fundamental limitations of high speed design is to have
a strong understanding of layout extraction
Most of the layouts are implemented using software tools like Magic,
Cadence, and Tanner Tools etc
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Definitions
Process of virtually simulating the design and checking
conformance with the specs
Advantages of Verification:
Early error detection
Fine tuning the design based on verification output
Reliable time metrics can be obtained
Verification in a M-S Environment
Multiple domains, multiple abstraction levels
Simulation cycle handles notion of time in discrete and
continuous values
Separate simulation engines, working with the same set
of signals
Output Analysis in Time/Frequency
Spice Circuit Simulator
First IC evaluation software
Has inbuilt components models for circuit elements
Allows different levels of models for varying accuracy
requirements
Provides accurate measurement for power and timing
Supports only structural models
Comparison of Spice and VHDL-AMS
Parameter
Behavioral Models
Multiple Analysis Modes
Digital Components
Mixed Time Modeling
Equation Set Analysis
Power/Area Analysis
VHDL-AMS
Spice
Evolution of M-S HDL’s
MAST – Developed during the early 80’s, required
expert users
VHDL-AMS – First version of the LRM in 1993,
shifted burden from user to simulator
Verilog-AMS – Extension of Verilog
Highlights of VHDL-AMS
Inclusion of continuous valued “quantities”
Allows design entry at the behavioral or structural levels
No concept of components like Spice, only equation sets
Analog solution based on numerical integration
VHDL-AMS Simulator Design
LIBRARIES
VHDL-AMS
SIMULATOR KERNEL
DAE
SOLVER
FES
TyVIS
DIGITAL
KERNEL
LEXICAL
ANALZER
SPICE
WARPED
Kernel
VHDL
Challenges in M-S Verification
Convergence – not always a guarantee
Large variations in time steps
Parasitic capacitances – model order and E.M effects
“Ripple Effect”: Whole design needs to be verified during
design modifications
High Frequency Analysis support still primitive
Verification
Verification is the process by which the correctness of the design and
implementation details is compared to the original specifications
Hardware description languages model complex systems A/D components
SOC’s have given rise to Analog and Mixed Signal (AMS) tools
These tools combine methods from traditional circuit simulators like SPICE
and digital simulation kernels like VHDL to deal with both of these
components
Any unsatisfactory or incorrect parameters can be detected and the design
can be modified to correct the errors or approach certain tolerance levels
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Electronic Circuit Design Process
A CMOS foundry takes a wafer of silicon and
processes it into an array of circuits (called die).
The wafer will also contain test structures, process
monitoring plugs and alignment reticules.
The individual die are diced from the wafer and
packaged into a variety of electronic devices.
Reference: R.J. Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition, John Wiley and Sons, 2005
MOSIS: The MOS Integration Service
MOSIS WEBSITE
The MOS Integration Service (MOSIS) provides a low cost method for
implementing CMOS designs.
The service works by purchasing fabrication runs from commercial CMOS
foundries and distributing the cost over a larger number of circuit designers.
For more information visit the MOSIS web page at www.mosis.org
Wafer Cleaning
Oxidation
Epitaxial
Growth
Lithography
Fabrication Process
Description
Implantation
Diffusion
NO
Metal Layer?
YES
Fabricated
Chip
Metal
Deposition
Annealing
Reference: R.J. Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition, John Wiley and Sons, 2005
Fabrication
The chip is fabricated (generally on lightly doped p-type or n-type silicon wafer)
using specific fabrication technology (i.e. TSMC 0.35µm or IBM 0.13µm
process etc.) that has been specified at circuit design level or before
A series of photolithographic mask layers are designed depending on type
process and number of steps involved
Subsequently, the whole design runs through several fabrication steps that
involve oxidation, photo-lithography (developing photo-resist layers, exposing
to UV and etching), implantation of p+ or n+ source/drain region, metallization
for forming contacts and developing field oxide for isolation of transistors
Fabrication processes are characterized by minimum feature size in a transistor,
gate oxide thickness, no. of poly and metal layers available for interconnections,
sheet resistances of different wells, doped regions, and metal and poly-silicon
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Testing Overview
Block Diagram of the
Photoreceiver
Photoreceiver Testing
Logic Analyzer Testing
Photoreceiver Circuit
Courtesy: Dr. Prosenjit Mal
Photoreceiver Layout
Example of Mixed Signal {Optical} Testing
Laser Diode
P1
LD Drive
Cubicle Splitter
P2
Optical Power Meter
P3
Fiber Coupler
Optical Fiber
Computer
(LabVIEW
Program)
P4
Detector/Receiver
Multi-meter
Power Source
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Example
Optical input power changes from 0 –
1mW
Most sensitive settings (000) switches
around 450µW
Least sensitive settings (111) switches
around 675µW
User can fine tune the range with Vadj
Vadj can be changed 0 – 3.3V
corresponds to input range shift of
90µW
General M-S Tests
Continuity Tests:
Detecting on Chip ESD
Validating Connectivity between Device and Tester
Fault Elimination
Breakdown Test:
Current Limit
Voltage Limit
Power Supply Test: IDDQ
Metal Errors – shorted traces
Implant/Diffusion errors – shorted substrate
Faulty ESD Clamps
Open/Floating Wells
Open/Floating Digital gate input
Reference: Prof. Forrest Brewer
www. bears.ece.ucsb.edu/class/ece224b/Lecture3mixedtest.ppt
General M-S Tests (Contd.)
Impedance Measurement
Z=V/I (Usually Z=DV/DI)
Force V, measure I (High Impedance)
Force I, Measure V (Low Impedance)
Defined Testing Levels
Reduce possibility of DUT damage
Increase accuracy of measurement
Power Analysis
Testing over Operation Range
Voltage/Current/Freq
Memory devices
Processors
Reference: Prof. Forrest Brewer
www. bears.ece.ucsb.edu/class/ece224b/Lecture3mixedtest.ppt
Testing
To facilitate the testing process, a number of test structures are evenly
distributed all over the chip
Test station equipment includes pattern generator, logic analyzer, probe
station, semi-conductor parameter analyzer, oscilloscope etc
While pattern generator and logic analyzer are used for digital test pattern
generations and measurements, other equipment facilitate probing of device
parameters and analog data measurements
The chip is run on through a number of test vector sets which are generated
from computer using various test algorithms
In conclusion, the circuit is verified for its functionalities and specifications.
Also tests are run for a period of time to check any variation of performance
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Outline of the Tutorial
Motivation
Overview
Detailed Design Process
Simulation with VHDL-AMS
Evaluation Process
Conclusions
Acknowledgements
Question and Answers
VHDL-AMS Overview
Capabilities
Language Overview
Solution Cycle
Solvability
Discontinuities
Predefined Attributes
Conclusion
References
Half Wave Rectifier
BEGIN
-- behavior
--diode equations
if( vDiode >= (-1.0 * Vt)) USE
eqn1_1: iDiode == saturation_current *
(exp(vDiode/Vt) - 1.0);
ELSIF ((vDiode < (-3.0 * Vt)) AND
(vDiode > -BV)) use
eqn1_2:
ELSE
iDiode == neg_sat;
eqn1_3: iDiode == neg_sat * (exp(-(BV
+ vDiode)/Vt) - 1.0 +
saturation_current);
END USE ;
--resistor equation
eqn2: v2 == 100.0 * i2;
--voltage source equation
eqn4: vs == 5.0 * sin(2.0 * 3.14 *
100000.0 *
real(time'pos(now)) * 1.0e-15 );
END behavior ;
Bouncing Ball Model
ENTITY bouncing_ball IS
END ENTITY bouncing_ball;
ARCHITECTURE simple OF
bouncing_ball IS
QUANTITY v: real;
QUANTITY s: real;
CONSTANT G: real := 9.81;
CONSTANT Air_Res: real := 0.1;
BEGIN -- specify initial
conditions using the break
statement
b1:BREAK v => 0.0, s => 30.0;
b2:BREAK v => -0.7*v WHEN
NOT(s'above(0.0));
velocity: v == s'dot ;
acceleration:
v'dot == -G;
END ARCHITECTURE simple;
∑-∆ Modulator
BEGIN
comp1: compr
port map(clk_enable , analog_vin, dac_out);
and1: andComp
port map(clk_in, clk_enable, enable_count);
count1: counter
port map(clear, enable_count, counter_op);
da_conv: dac
port map(counter_op, dac_out, electrical'reference);
M-S Simulation
Mixed representations of time, synchronization
Multiple physical domains
Conservative and non-conservative models
Solvability, Convergence
VHDL-AMS – VHDL 1076.1-1999
Superset of VHDL 1076
Analysis types – transient, noise, small signal frequency
Solve Differential Algebraic Equations (DAE)
Tolerances, discontinuity handling
Language Overview
Nature definitions
Terminals and Quantities
Quantity Attributes – Implicit quantities/signals
Mixed-signal interfaces
Mixed-signal descriptions of behavior
Quantities
. . .
ARCHITECTURE sinebehavior OF sineSource IS
QUANTITY Irsine THROUGH ta2 TO tb2;
QUANTITY resistor: REAL;
. . .
Represents an unknown in the set of DAEs
Continuous time waveform
Pre-defined attributes create implicit quantities
Types of Quantities
ENTITY example IS
PORT (
PORT
QUANTITY interface_q: REAL;
QUANTITY
TERMINAL elec_p, elec_n: ELECTRICAL);
END ENTITY example;
BRANCH QUANTITY
ARCHITECTURE simple OF example IS
QUANTITY v1, v2 ACROSS i1, i2, i3 THROUGH
elec_p TO elec_n;
FREE QUANTITY
QUANTITY free_q: REAL;
. . .
Terminal
ENTITY diode IS
. . .
PORT ( TERMINAL anode, cathode: ELECTRICAL);
END ENTITY diode;
Represents a node in an electrical circuit
Support for structural composition with conservative semantics
Belongs to a NATURE
Electrical Systems Environment
PACKAGE electrical_system IS
SUBTYPE voltage IS REAL TOLERANCE “default_voltage”;
SUBTYPE current IS REAL TOLERANCE “default_current”;
SUBTYPE charge IS REAL TOLERANCE “default_charge”;
NATURE electrical IS
voltage ACROSS
-- across type
current THROUGH
-- through type
electrical_ref REFERENCE;
-- reference type
ALIAS ground IS electrical_reference;
NATURE electrical_vector IS
ARRAY ( NATURAL RANGE <>) OF ELECTRICAL;
END PACKAGE electrical_system;
Nature Definition
Electrical nature in package electrical system
Represents a physical discipline/energy domain
Each node is of a certain nature
Defines the types of quantities incident on the terminal
Subnature declaration – different tolerance levels
Other nature definitions: thermal, translational, rotational,
fluidic, magnetic, etc..
Relation between Elements
Terminal
Nature
Structure
Information
Type
Information
Quantity
Simultaneous Statement(1)
ARCHITECTURE simple OF bouncing_ball IS
. . .
BEGIN
. . .
velocity: v == s'dot ; acceleration:
v'dot == -G;
. . .
Expresses relationship between quantities – used by the analog solver
May appear anywhere a concurrent statement may appear
Simultaneous Statements(2)
LHS and RHS – Floating point type
One quantity must appear in each simultaneous statement
Tolerance group determined by the quantities
Other Forms of Simultaneous Statements
Simultaneous IF statement
Simultaneous CASE statement
Simultaneous procedural statement – functions
DAE Solvers and Tolerance
z
z
z
z
DAE – Differential Algebraic Equations
Solver – Uses numerical integration to reduce DAE’s to
linear/non-linear equations
Tolerance – Accept all solutions within a certain amount
of variance
Necessary to adjust for accuracy of numerical methods
Simulation Cycle
Analysis
Syntax, Semantics
Elaboration
Flatten out
processes & signals
Digital/Analog Solver
Simulation
Sierra – VHDL-AMS Simulator
SCRAM
Intermediate Representation
C++
VHDL-AMS
TyVIS/SIERRA
PLOTTER
Graphical
Operation
Simulation
Operation
Analog/DAE Solver
SEAMS: Simulation Environment for VHDL-AMS – Frey et al., 1998 Winter Simulation Conference
Solvability
General Solvability - # of equations equals # of unknown
quantities
For VHDL-AMS:
#(Equations) = #(through quantities) + #(free
quantities) + #(interface quantities of mode OUT)
Each scalar simultaneous statement creates one
equation
Sample Solvability Problem
ENTITY battery IS
ENTITY battery IS
PORT ( TERMINAL plus, minus:
PORT ( TERMINAL plus, minus:
electrical );
electrical );
END ENTITY battery;
END ENTITY battery;
ARCHITECTURE simple OF battery IS
ARCHITECTURE simple OF battery IS
CONSTANT v_nominal: REAL := 9.0;
CONSTANT v_nominal: REAL := 9.0;
QUANTITY v ACROSS plus TO minus;
QUANTITY v ACROSS i THROUGH plus TO
minus;
BEGIN
v = = v_nominal;
END ARCHITECTURE simple;
BEGIN
v = = v_nominal;
END ARCHITECTURE simple;
Solvability – Simultaneous IF Statement
ENTITY sfgAmp IS
GENERIC ( gain: REAL := REAL’HIGH);
PORT (QUANTITY input: IN REAL;
QUANTITY output: OUT REAL);
END ENTITY sfgAmp;
ARCHITECTURE ideal OF sfgAmp IS
BEGIN
IF gain /= REAL’HIGH USE
output = = gain * input;
ELSE
input = = 0.0;
END USE;
END ARCHITECTURE ideal;
Same # in each USE clause
Discontinuities
BEGIN -- specify initial
b1:BREAK v => 0.0, s => 30.0;
b2:BREAK v => -0.7*v
WHEN NOT(s'above(0.0));
velocity: v == s'dot ;
acceleration: v'dot == -G;
END ARCHITECTURE simple;
BREAK !
Break Statement
Prompts analog solver to reset its state
Coincides with a digital event
Explicitly say which event – to improve simulation speed
Is also employed to specify initial conditions
A model not having a BREAK at a discontinuity is
erroneous!
Predefined Attributes
z
Implicit signals/quantities created:
Quantity Attributes
Q’above(E), Q’dot, Q’integ,
Q’slew(n1,n2)
Frequency domain: Q’ztf( num, den, t,
initial_delay), Q’ltf( num, den)
z
Signal Attributes
S’ramp( n1, n2), S’slew( n1, n2)
Summary
Use VHDL-AMS for your M-S circuits!
Some Sources:
www.ececs.uc.edu/~dpl : University of Cincinnati
www.syssim.ecs.soton.ac.uk: Southampton, UK
www.dolphin.fr: Dolphin Systems - Smash
www.mentor.com: Mentor Graphics – Advance MS
References
z
z
z
z
The System Designer's Guide to VHDL-AMS – Ashenden et al.
Modeling Semicondutor Devices using the VHDL-AMS Language
– KasulaSrinivas, MS Thesis, University of Cincinnati, 1998.
Introduction to the VHDL-AMS Language – Christen et al.,
Tutorial Presented at DAC, 1999
VHDL 1076.1 LRM – IEEE Press, 2003
Outline of the Tutorial
Motivation
Overview
Detailed Design Process
Simulation with VHDL-AMS
Evaluation Process
Conclusions
Acknowledgements
Question and Answers
Performance Evaluation using R-Software
Introduction
‘R’ statistical software was initially introduced by Ross Ihaka and
Robert Gentleman at Department of Statistics of University of
Auckland, New Zealand during 1990s
Since 1997: international “R-core” team of 15 people collaborated in an
effort to make it an open source
R is a language and environment for statistical computing and graphics.
R provides a wide variety of statistical (linear and nonlinear modelling,
classical statistical tests, time-series analysis, classification, clustering,
.
...) and graphical techniques, and is highly extensible
Reference:
1. Huang Chen - www.math.ntu.edu.tw/~hchen/ Prediction/notes/R-programming.ppt
2. The R Project for Statistical Computing - http://www.r-project.org/
Highlights of R
R is a language and environment for data manipulation, calculation
and graphical display:R is similar to the award-winning S system, which was developed
at Bell Laboratories by John Chambers et al.
a large, coherent, integrated collection of intermediate tools for
interactive data analysis,
graphical facilities for data analysis and display either directly at
the computer or on hardcopy
a well developed programming language which includes
conditionals, loops, user defined recursive functions and input
and output facilities.
Reference:
1. Huang Chen - www.math.ntu.edu.tw/~hchen/ Prediction/notes/R-programming.ppt
2. The R Project for Statistical Computing - http://www.r-project.org/
The core of R is an interpreted computer language:It allows branching and looping as well as modular programming
using functions.
Most of the user-visible functions in R are written in R, calling
upon a smaller set of internal primitives.
It is possible for the user to interface to procedures written in C,
C++ or FORTRAN languages for efficiency, and also to write
additional primitives
Reference:
1. Huang Chen - www.math.ntu.edu.tw/~hchen/ Prediction/notes/R-programming.ppt
2. The R Project for Statistical Computing - http://www.r-project.org/
What R Does & Does Not ?
Data handling and storage
Not a database, but connects to DBMSs
Matrix algebra
Hash tables and regular expressions
No graphical user interfaces, but
connects to Java, TclTk
High-level data analytic and
statistical functions
Language interpreter can be very slow,
but allows to call own C/C++ code
Graphics
No spreadsheet view of data, but
connects to Excel/MsOffice
Programming language: loops,
branching, subroutines
No professional / commercial support
Reference:
1. Huang Chen - www.math.ntu.edu.tw/~hchen/ Prediction/notes/R-programming.ppt
2. The R Project for Statistical Computing - http://www.r-project.org/
Data Analysis and Presentation
The R distribution contains functionality for large number of
statistical procedures.
Linear and generalized linear models
Nonlinear regression models
Time series analysis
Classical parametric and nonparametric tests
Clustering
Smoothing
Large set of functions which provide a flexible graphical
environment for creating various kinds of data presentations.
Reference:
1. Huang Chen - www.math.ntu.edu.tw/~hchen/ Prediction/notes/R-programming.ppt
2. The R Project for Statistical Computing - http://www.r-project.org/
References
z “The New S Language: A Programming Environment for Data
Analysis and Graphics” by Richard A. Becker, John M. Chambers
and Allan R. Wilks (the “Blue Book”) .
z “Statistical Models in S” edited by John M. Chambers and Trevor J.
Hastie (the “White Book”)
z Internet site (via http://cran.r-project.org).
Reference:
1. Huang Chen - www.math.ntu.edu.tw/~hchen/ Prediction/notes/R-programming.ppt
2. The R Project for Statistical Computing - http://www.r-project.org/
WHAT IS A SYSTEM ?
Factors
System
Inputs
SYSTEM
Responses
Courtesy: Dr. Harold Carter
System
Outputs
Experimental Research
Define
Define
System
System
Define system outputs first
Then define system inputs
Finally, define behavior (i.e., transfer function)
Identify
Identify
Factors
Factors
and
and Levels
Levels
Identify system parameters that vary (many)
Reduce parameters to important factors (few)
Identify values (i.e., levels) for each factor
Identify
Identify
Response(s)
Response(s)
Identify time or space effects of interest
Design
Design
Experiments
Experiments
Identify factor-level experiments
Courtesy: Dr. Harold Carter
Create and Execute System; Analyze Data
Define
Define
Workload
Workload
Workloads are inputs that are applied to system
Workload can be a factor (but often isn't)
Create
Create
System
System
Create system so it can be executed
Real prototype
Simulation model
Empirical equations
Execute
Execute
System
System
Execute system for each factor-level binding
Collect and archive response data
Analyze
Analyze &
& Display
Display
Data
Data
Courtesy: Dr. Harold Carter
Analyze data according to experiment design
Evaluate raw and analyzed data for errors
Display raw and analyzed data to draw conclusions
Examples
ANALOG SIMULATION
Which of three solvers is best?
What is the system?
Responses
Fastest simulation time
Most accurate result
Most robust to types of circuits
being simulated
Factors
Solver
Type of circuit model
Matrix data structure
Courtesy: Dr. Harold Carter
EPITAXIAL GROWTH
New method using nonlinear temp profile
What is the system?
Responses
Total time
Quality of layer
Total energy required
Maximum layer
thickness
Factors
Temperature profile
Oxygen density
Initial temperature
Ambient temperature
Generic Model for Network Protocol
Data file “latency.dat”
Latency
22
23
19
18
15
20
26
17
19
17
Courtesy: Dr. Harold Carter
System: wireless network with new protocol
Workload:
10 messages applied at single source
Each message identical configuration
Experiment output
Roundtrip latency per message (ms)
Data Distribution
Box Plot
Summary
Latency
Min. :15.00
1st Qu.:17.25
Median :19.00
Mean :19.60
3rd Qu.:21.50
Max. :26.00
Courtesy: Dr. Harold Carter
Scatter Plot
Mean: 19.6 ms
Variance: 10.71 ms2
Std Dev: 3.27 ms
Verify Model Preconditions
Check randomness
Use plot of residuals around mean
Residuals appear random
Courtesy: Dr. Harold Carter
Check normal distribution
Use quantile-quantile plot
Pattern adheres consistently along ideal Q-Q line
Confidence Intervals
Sample mean vs Population mean
CI: > 30 samples
CI: < 30 samples
Courtesy: Dr. Harold Carter
Reference: Raj Jain, “The Art of Computer Systems Performance Analysis,” Wiley, 1991.
T- Test Analysis
t.test (dataset1,conf.level = 0.99)
One Sample t-test
data: dataset1
t = 18.9382, df = 9, p-value = 1.468e-08
alternative hypothesis: true mean is not
equal to 0
99 percent confidence interval:
16.2366 22.9634
sample estimates:
mean of x
19.6
Courtesy: Dr. Harold Carter
t.test (dataset1,conf.level = 0.95)
One Sample t-test
data: dataset1
t = 18.9382, df = 9, p-value = 1.468e-08
alternative hypothesis: true mean is not
equal to 0
95 percent confidence interval:
17.25879 21.94121
sample estimates:
mean of x
19.6
Scatter and Line Plots
Regression Plot
Depth
1
2
3
4
5
6
7
8
9
10
Resistance
1.689015
4.486722
7.915209
6.362388
11.830739
12.329104
14.011396
17.600094
19.022146
21.513802
Residual Plot
Normally Distributed Error
Linear Regression Statistics
model = lm(Resistance ~ Depth)
summary(model)
Residuals:
Min
1Q Median
3Q
Max
-2.11330 -0.40679 0.05759 0.51211 1.57310
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -0.05863 0.76366 -0.077 0.94
Depth
2.13358 0.12308 17.336 1.25e-07 ***
--Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1
Residual standard error: 1.118 on 8 degrees of freedom
Multiple R-Squared: 0.9741, Adjusted R-squared: 0.9708
F-statistic: 300.5 on 1 and 8 DF, p-value: 1.249e-07
Courtesy: Dr. Harold Carter
Comparing Two Sets of Data
Example: Consider two wireless
different access points. Which one
is faster?
Inputs: same set of 10 messages
communicated through both access
points.
Approach:
Take difference of data and
determine CI of difference.
If CI straddles zero, cannot tell
which access point is faster.
Response (usecs):
Latency1 Latency2
22
19
23
20
19
24
18
20
15
14
20
18
26
21
17
17
19
17
17
18
Courtesy: Dr. Harold Carter
CI95% = (-1.27, 2.87) usecs
Confidence interval straddles zero.
Thus, cannot determine which is faster with
95% confidence
Plots with Error Bars
Execution time of SuperLU linear
system solution on parallel computer
Ax = b
For each p, ran problem multiple
times with same matrix size but
different values
Determined mean and CI for
each p to obtain curve and error
intervals
Courtesy: Dr. Harold Carter
Statistical Point Analysis
Output from Model
Mean, Std Dev,
Variance, Box Plot
Check for Randomness
Residual Analysis
T-test Analysis
Confidence Interval
Check for Distribution
Q-Q Plot
Specification
Compare
Decision
Outline of the Tutorial
Motivation
Overview
Detailed Design Process
Simulation with VHDL-AMS
Evaluation Process
Conclusions
Acknowledgements
Question and Answers
Conclusions
Increasing trend towards highly integrated systems, there is an ever growing
demand for hardware based on SOC technology
Development of these complex components places correspondingly
multifarious demands on the design engineer,
New CAD and simulation resources are providing system and chip
designers with the design tools necessary for integrated CMOS hardware
New CAD tools can be used with a standard design methodology to produce
mixed technology designs
Integrate analog, digital and mixed signal into a single device design that
can be fabricated through a conventional CMOS fabrication process
Design methodology and new CAD/simulation tools allow the design
engineer to focus on the intricacies of mixed mode integrated circuit design
(ex noise reduction, signal cross-talk, etc.) without loosing site of chip
functionality or system level performance specification
Reference: Prashant Bhadri, Raghuram Srinivasan, Prosenjit Mal, Fred Beyette Jr., Harold Carter, “Design and
Analysis of Mixed Mode Integrated Circuits” IEEE Potentials Magazine, February 2005, pp: 6-11
Outline of the Tutorial
Motivation
Overview
Detailed Design Process
Simulation with VHDL-AMS
Evaluation Process
Conclusions
Acknowledgements
Question and Answers
Dr. Carla Purdy
Dr. Harold W Carter
Dr. Fred R Beyette Jr.
Associate Professor
Professor and Dept. Head
Associate Professor
Department of ECECS
Department of ECECS
Department of ECECS
University of Cincinnati
University of Cincinnati
University of Cincinnati
Aaron C. Barnes, M.S
Alla S. Kumar
L. Ramasamy, M.S
Co-Director, Microsurgery
Graduate Student
Doctoral Researcher
Advanced Design Lab
Department of ECECS
Department of ECECS
Doheny Retina Institute
University of Cincinnati
University of Cincinnati
Univ. of Southern California
Question and Answers