TCL/Tk Based Environment for Mixed-Signal Circuit Design

1. TCL/Tk Based Environmentfor Mixed-Signal Circuit Design • System Description • Software Architecture • Examples • Future Directions • Summary

2. System Description • Designing Circuits • Software Architecture • Celerity • Camelot • New Environment

3. Designing Circuits Make netlist Shrink netlist Run Simulator set libraries read circuit simulate run plotter read in results plot Create/modify schematic Designer Typically put in a script

4. Software Architecture Netlist Camelot Celerity (optional shrink) Output File Plot Script Circuit TCL Code Plotter Start-up TCL Code

5. Celerity • Analog Circuit Simulator created by Bell Labs Design Automation • TCL/Tk - C - C++ • Many powerful features, modular design, Built-in plotting package • Cadence purchased BLDA from Lucent • Celerity now being phased out by Cadence Celerity User Interface (TCL/Tk) Output file Celerity C++ Engine Plotter

6. Camelot • Originally developed for use with general optimization problems • First used only for parameter extraction • Main Objects • data table • parameter table • model handler • optimizer handler • Additional uses arose • Optimization of small number of performances to targets - worst-case file generation • Data manipulation and viewing • Driving other programs and collecting results • No Camelot/Spectre interface - Spectre is a batch simulator • Future of Camelot uncertain

7. Camelot/Celerity Interface • Object-based paradigm • Celerity process is created and a communications link is established • A controlling handle command (object) is created for communication with the process • Object has low and high-level methods for sending and retrieving information from the remote process • A registry of objects is maintained by the class • UnixShell> tcad camelot • Camelot> celerity c • Camelot> c circuit “ • .TITLE TRY IT • V1 1 0 1.0 • M1 1 1 0 0 NS1 • .OUT ALL • .END • “ [lcmos -tech 035-3V] • c command “.DC OP; .OP *”

8. Camelot Objects • Data Objects • Tables of numeric data • Circuit Object • Contains netlist, library, and analysis information • Parameter Objects • Tables of parameter settings (initial, min, max, nominal) • Model Objects • Interface between Optimizer and User Defined Model • Optimizer Objects • Interface with Error Minimizer, Contains information to • control and query the optimizer

9. Circuit Object • Methods (Partial list): • circuit {ckt_lines}: Establish Main testbench circuit • monitor {args}: Specify node voltages or element currents • setlibs {args}: Establish paths to library files • command {commands}: Issue a command to the Celerity simulator • ic {args}: Establish initial conditions • info {args}: Request information about the circuit • node {node}: Request node voltage • element {element item}: Get information about an element in the circuit • op {file}: Dump operating points to a file if specified or to screen if not • win: Display text window with interactive connection to celerity • measurement {name body}: Define measurement to be performed for • each case file • analysis_data {analysis {way advice}}: Return data object containing • analysis data

10. Data Object • Creating Data Object: • data d0 • Reading Data • d0 read meas.dat • Accessing Data • Get First Entry • d0 get 0 0 • Set Last column in First Row to 1.1 • d0 set 0 last 1.1 • Labels • Label 3rd column as Vgs • d0.col label 2 Vgs • Add Four Columns • d1.col extend 4 • Plot Data • d0 plot Vgs Ids

11. Parameter Objects • Similar to Data Object • Row Labels are Parameter Names • New values added as a new column after most recent iteration EXAMPLE PARAMETER FILE, p.dat BETA EXCLUDE 25E-4 1E-4 50E-4 LAMDA EXCLUDE 0.0 0.0 1.0 VTH EXCLUDE 0.8 0.4 1.2 AST INCLUDE 15 2 50 par p p read p.dat Name include/exclude nominal minimum maximum

12. Model Objects Contains pointers or hooks to routines which evaluate the error residual of a model. • Five types of hooks: • init: Initialize variables • getdim: Number of model outputs • eval: Evaluate model with current set of parameters • error: Calculates residual of measured vs modeled results • term: Terminates model

13. Optimizer Objects • Interface to Error Minimizer • Currently only “Arthur” optimizer • Options: • - abstol • - ftol • - reltol • - atol • - xtol • - maxeval • - maxiter • - stepsize • - journal • - verbose • Creating the Optimizer: • arthur x0 • x0 config -maxiter 50 -reltol 1e-10 • Running the Optimizer: • x0 extract m0 d0 p0

14. Writing the Script • Problem: Designers have little time to code (or learn languages) • Procedure “makeproc”: • Saves designer from writing common code proc makeproc {ckt} { ... set p “procedure blank {…} {… }” regsub $p blank $ckt x set fptr [open $ckt.tcl w] puts $fptr $x … } Util.tcl

15. Components of the Script • Setup Global Variables (temperature, library path, etc) • Initialize list of valid analyses • Call post-layout procedure if necessary • foreach anal $anallist { • Save previous results • Shrink circuit if required • Read circuit • switch $anal { • op {…} • ss {…} • nv {…} • refresh {…} • } • Save Results • Call View Procedure • } • foreach anal $valid { Make Button Panel }

16. Post Layout Procedure “subpost” Netlist from simulator .MAIN ckt X1 1 0 A X2 2 0 B .END .subckt A … .finis .subckt A … .finis .subckt B … .finis .subckt B … .finis Post-layout directory “post” Netlists from Layout Extraction Current Working Directory

17. View Procedure “view” • proc view {name file {label “”}} { • Create Script File for Plotter • find out how many blocks (nblocks) • exec ttcad celplot -b file_name • } .cl .re $file .bl 1 $label=$name .bl 2 $label=$name … .ti $file [date] Celerity plotting package

18. Examples

19. Examples (cont.)

20. Future Directions Many Enhancements are possible • Display analysis scripts on screen and allow for editing • Expand plot script to handle more complicated cases • Use BLT and data object features for better viewing • Include math on results • Include post-layout feature in GUI • Provide GUI for circuit object methods • Add more elaborate version control • Don’t re-read the circuit if it hasn’t changed • Incorporate library panel into circuit panel • Add Optimization Features to circuit panel

21. Summary • TCL/Tk works well for gluing CAD Components • Saves Designer’s time for iteration during design phase • Allows Designers to share scripts easily • Keeps all scripts for circuit in one place • Automates post-layout simulation with keyword • TCL features allow for easy post-processing of simulation results • BLT permits nice graphic interfaces (pole-zero plots, text windows, etc.)