Verilog-A Clock Driver — Design & Debugging

Tech Stack: SmartSpice (Silvaco), Gateway, Verilog-A, PWL, SmartView

I designed a reusable Verilog-A clock/pulse driver for RRAM array for AI semiconductor research, integrated it with SmartSpice via Gateway, and documented key troubleshooting & debugging steps (imports, control-file linkage, symbolization).

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  • Goal

    Generate clean, parameterized square waves (VH, VL, freq, duty) to drive WL/BL/SL and stop or adapt based on measured conductance.

  • Method (Brief)

    Verilog-A clock block → Gateway import/embedding → SmartSpice control-file binding → symbol hookup → waveform verify (SmartView) & console debug.

  • Design Highlights

    • Duty-cycle–based clocking; fixed magnitude/width options for sweeps.

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    • @timer-style scheduling and transient timing control for repeatable toggles.
    • PWL fallback for corner cases; parameter guards to avoid meta-stability.
    • “Stop-on-target” logic (write/verify loop ready) when conductance meets threshold.
    va code clock random

  • Results

    • Clean 50–80% duty clocks for WL/BL/SL; stable toggling across PVT corners.
    • Resolved “no-output” cases and reduced bring-up time; ready for write-verify automation.
    • Scales to large arrays when embedded; control-file method works with corrected includes.

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  • EDA Integration (Gateway & SmartSpice)

    • Verilog-A import paths tried as: (1) direct import (symbol), (2) embedded definition, (3) control-file (.ctr) include.
    • Early attempt of method (3): output voltage not observable → fixed by netlisting order and symbol pin-mapping; method (2) proved most robust in large arrays.
    • Common pitfalls: .include/.verilog/.hdl header mix-ups, library scope, and control-file search paths.

  • Troubleshooting Checklist

    1) Ensure .va compiled before symbol instantiation; 2) verify pin order and units; 3) set initial conditions to avoid DC-op traps; 4) confirm viewer probes on the driver output node; 5) when duty<→write time matters, sweep duty first (frequency often secondary within the safe Vwrite window).

  • Next

    • Add programmable burst/idle patterns; • expose API for testbenches; • ship as a lab “clock IP” cell.

Code: Code