VHDL-AMS VHDL-Analog and Mixed Signal Extensions

2 Overview IEEE Std :  Extension to VHDL to support the description and simulation of analog and mixed-signal circuits and systems VHDL-AMS = IEEE Std IEEE Std  VHDL-AMS is a strict superset of IEEE Std  Any model valid in VHDL 1076 is valid in VHDL-AMS and yields the same simulation results

3 Why Needed? Many of today’s designs include at least some continuous characteristics:  System design −Mixed-signal electrical designs (Cell phones, …) −Mixed electrical/non-electrical designs (Music players, Digital Cameras, Samand) −Modeling design environment (Temperature, humidity, …)  Analog design −Analog behavioral modeling and simulation  Digital design: As frequency increases, and technology advances (DSM effects), 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) Designers want a uniform description language

4 When Digital Becomes Analog? Frequency (GHz)

5 Issues in Mixed-Signal 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

6 Current Status of Mixed-Signal Design Fabrication technology:  Current technology supports mixed-signal circuits on a chip  And even mixed electro-mechanical systems on a chip (MEMS) Design tools:  Analog and Mixed-Signal (AMS) modeling and simulation  AMS synthesis (still in research stage)

7 Advantages of Verification Advantages of Modeling and Simulation:  Early error detection  Fine tuning the design based on verification output  Reliable time metrics can be obtained

8 Simulation in an M-S Environment Challenges:  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

9 Highlights of VHDL-AMS  Inclusion of continuous valued “quantities”  Allows design entry at the behavioral or structural levels  Analog solution based on numerical integration −Continuous models based on “differential algebraic equations” (DAE)

10 Nature Definition:  Nature represents a physical discipline/energy domain Samples:  Electrical  thermal,  fluidic,  magnetic,  ….

11 Terminal Terminal:  Represents a node in an electrical circuit

12 Quantity  Represents an unknown in the set of DAEs  May be the value (e.g. voltage level) across or through two terminals.  Continuous-time waveform.  For any quantity Q, the attribute name Q’Dot denotes the derivative of Q w.r.t. time. −Q’Dot is itself a quantity  Q’Integ: integral of Q w.r.t. time.

13 Simultaneous Statement Simultaneous Statement:  Expresses relationship between quantities. − Analog solver is responsible for computing the values of the quantities such that the relationships hold (subject to tolerances)  May appear anywhere a concurrent statement may appear.  Statement is symmetrical w.r.t. its LHS and RHS. architecture H2 of Vibration is... begin x1’dot’dot == -f*(x1 - x2) / m1; x2’dot’dot == -f*(x2 - x1) / m2; xs == (m1*x1 + m2*x2)/(m1 + m2); energy == 0.5*(m1*x1’dot**2 + m2*x2’dot**2 + f*(x1-x2)**2); end architecture H2;

14 Simultaneous Statement Other Forms of Simultaneous Statements:  Simultaneous IF statement  Simultaneous CASE statement  Simultaneous procedural statement – functions 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;

15 Branch Quantities Declared between two terminals  Plus terminal and minus terminal  Minus terminal defaults to reference terminal of nature vd is an across quantity:  it represents the voltage between terminals anode and cathode −vd= vanode - vcathode id and ic are through quantities:  they represent the currents in the two parallel branches −Both currents flow from terminal anode to terminal cathode architecture Level0 of Diode is quantity vd across id, ic through anode to cathode;... begin... end architecture Level0;

16 Example: Diode library IEEE, Disciplines; use Disciplines.electrical_system.all; use IEEE.math_real.all; entity Diode is generic (iss: REAL := 1.0e-14; n, af: REAL := 1.0; tt, cj0, vj, rs, kf: REAL := 0.0); port (terminal anode, cathode: electrical); end entity Diode; architecture Level0 of Diode is quantity vd across id, ic through anode to cathode; quantity qc: charge; constant vt: REAL := ; -- thermal voltage begin id == iss * (exp((vd-rs*id)/(n*vt)) - 1.0); qc == tt*id - 2.0*cj0 * sqrt(vj**2 - vj*vd); ic == qc’dot; end architecture Level0;

17 Quantities in Various Natures Electrical  voltage: across  current: through Translational  position: across  force: through Thermal  temperature: across  power (or heat-flow): through Fluidic  pressure: across  flow-rate: through

18 References Reference Site:  Reference Book:  The System Designer's Guide to VHDL-AMS (The Morgan Kaufmann Series in Systems on Silicon) by Peter J. Ashenden, Gregory D. Peterson, Darrell A. Teegarden Tools:  Mentor Graphics SystemVision: −a downloadable version for educational purposes: −  University of Cincinnati VHDL-AMS simulator (SEAMS)  Infineon Technologies VHDL-AMS Environment  Analogy TheHDL Mixed Signal Simulator  FTL Systems VHDL-AMS Compiler/Simulator  LEDA VHDL-AMS Front-end tools  University of Southampton VHDL-AMS Analyzer  University of Frankfurt Java VHDL-AMS Parser Models: 