Self-Calibrating LLM-Based Analog Circuit Sizing with Interpretable Design Equations

Abstract: We present a self-calibrating framework for analog circuit sizing in which a LLM derives topology-specific analytical design equations directly from a raw circuit netlist. Unlike existing AI-driven sizing methods where the model proposes parameter adjustments or reduces a search space, the LLM produces a complete Python sizing function tracing each device dimension to a specific performance constraint. A deterministic calibration loop extracts process-dependent parameters from a single transistor-level simulation, while a prediction-error feedback mechanism compensates for analytical inaccuracies. We validate the framework on six operational transconductance amplifier (OTA) topologies spanning three families at two process nodes (180 nm and 40 nm CMOS). All 12 topology-node combinations achieve all specifications, converging in 2-9 simulations for 11 of 12 cases, with one outlier requiring 16 simulations due to an extremely narrow feasible region. Despite large initial prediction errors, convergence depends on the measurement-feedback architecture, not prediction accuracy. This one-shot calibration automatically captures process-dependent variations, enabling cross-node portability without modification, retraining, or per-process characterization.