1. Mixed-Digital/Analog Simulation and Modeling Research
Prof. Hal Carter
11 February 2005

2. A Mixed Signal Mixed Domain RF chip
RF receivers
Microprocessor
Frequency domain
Digital Core
Time domain
A/D converters
Memory Units
RF Transmitters
Frequency domain
Analog Core
Time domain
Mixers
Courtesy Acapella Ltd

3. Context Simulation Modeling Electronic Design Automation
Digital/Analog Electronics
VLSI
Data Analysis Applications

4. VHDL-AMS Example ir il n2 dout n3 entity rl_series is
port (dout: out bit;);
generic (R : real := 2.0;
V : real := 10.0 ;
L : real := 4.0 );
end entity ;
architecture behavior of rl_series is
terminal n1, n2, n3 : real;
quantity Vr across ir through n1 to n2;
quantity Vl across il through n2 to n3;
quantity vs across n1 to n2;
begin
Vs == V;
dout <= NOT a2d (n2);
Vr == ir * R;
Vl == L * il’dot;
end behavior ; ir R n1 n2
dout Vr Vl il Vs n3

5. Top Down Design with Mixed-Signal Current Language Scope
Technology Domain
Timing Model
Current State of VHDL-AMS
Continuous
Current State of Digital Design Representation (after synthesis)
Mixed
Distributed parameter
Future State of Analog Design Representation
Lumped parameter
Discrete
Digital
Current State of VHDL
Time
Frequency
Physical
Domain Representation

6. Mixed-Signal Design Digital/Analog Behavioral Design Reqts
Circuit
Design
Layout
VLSI
Circuit
Simulate
Simulate
Analyze
Simulation
Results
Extract &
Simulate
Analyze
Simulation
Results
Analyze
Simulation
Results
Fabricate

7. Behavioral Design Analog Behavioral Design Digital Behavioral Design
Algorithm
Transfer functions
Signal flow
Interface signals
Voltage/current sources
Waveforms
Functions
Digital Behavioral Design
Algorithm
Sequence of actions
Functions
Finite State Machines
Interface signals
Sequences of numbers
integer or real types

8. Circuit Design Digital Circuit Design Analog Circuit Design
Component networks
Register transfer Level
Gates & latches
Interfaces
Bit scalars and vectors
Timing
Discrete and accurate
Analog Circuit Design
Component networks
Constitutive equations
Kirchoff equations
Interfaces
Terminals, voltages, currents
Timing
Continuous & accurate

9. Mixed-Signal Modeling
Methodology
Behavioral level (System)
Function is primary
Include all primary and secondary effects (e.g., noise)
Use simulation results as “golden” behavior
Subsystem level
Subsystem function is primary
Include all primary and secondary effects in each subsystem
Compare simulation results with behavioral level results
Component level (Circuit)
Component function is primary
Sinclude allprimary and secondary effects in each component
Compare simulation results with subsystem level results

10. Sigma-Delta Converter Example
Behavioral Level
Behavior
output(n) = mult_noise * input(t) + add_noise
where output(n) is type “discrete bit”
and input(t) is type “continuous real”

11. Sigma-Delta Converter
Subsystem Level
Integrate
Discretize
Serial-to-
parallel
DAC
Int_output = mult_noise * integrate (Int_input) + add_noise

12. Sigma-Delta Converter
Integrate
Discretize
Serial-to-
parallel
DAC
Voltage = (mult_noise * resistance + add_noise) * Current

13. Mixed-Signal Simulation
C++
Compiler
Run-Time
System
Syntax
Lexical
Analyzer
Static
Semantic
Analyzer
C++
Code
Generator
Library
Pre-
processor
Elaboration
Built-in
Attributes
Front end
additions
VHDL-AMS
Model
Library
Manager
Initialization
Discrete
Event Kernel
Frequency
Kernel
Continuous
Time kernel
Output
processing

14. Data Analysis Many random variables in models
Need thousands of simulation runs
Simulator must be very fast
Need parallel simulator
Need to design experiments for efficiency
Design of Experiments
Data is very complex
Need to analyze data statistically

15. Molecular Computers Idea: Predict logic and memory circuits,
Develop models for devices and circuits
Create an algebra and design method for nanotube electronics