Symbolic Circuit Simulation Using MTBDDs for Analog Nodes
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Solution Overview
Problem
Current methods for simulating digital circuits with analog components are inefficient and inaccurate, as they either require time-consuming manual replacement of analog devices with digital models or slow symbolic analysis, which are not scalable for larger circuits.
Innovation Solution
The method models transistors in analog circuits as variable resistors using piece-wise linear lookup tables and Multi-Terminal Binary Decision Diagrams (MTBDDs) to compute node voltages and delays, allowing for efficient simulation and verification of digital circuits with analog components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual replacement of analog devices with digital models is performed, then verification accuracy is improved, but time consumption and error probability increase
Solution Approach 1:
The patent replaces manual mechanical replacement of analog devices with digital models by introducing an automated computer-implemented method. The simulation program automatically identifies analog devices, determines their small-signal parameters, and generates equivalent digital models without manual intervention, thereby maintaining verification accuracy while eliminating time consumption and human error.
Solution Approach 2:
The simulation program performs self-service by automatically analyzing the circuit schematic, identifying analog devices, computing their small-signal parameters, and generating equivalent digital models. This automated self-service process eliminates the need for manual model replacement while ensuring accuracy through systematic computational analysis.
2Measurement precision
If symbolic analysis in Mathematica is used, then circuit behavior is fully described, but simulation speed decreases significantly
Solution Approach 1:
The patent segments the circuit analysis into two parts: analog devices are identified and analyzed separately to extract small-signal parameters, while the rest of the digital circuit undergoes conventional symbolic simulation. This segmentation allows efficient processing of the majority of the circuit while applying detailed analysis only where necessary, maintaining both accuracy and speed.
Solution Approach 2:
The patent changes the parameters of analog devices from their original complex analog characteristics to simplified small-signal parameters (gain, bandwidth, impedance). This parameter transformation enables the analog devices to be represented as equivalent digital models that can be processed efficiently by symbolic simulation tools, thereby improving simulation speed while preserving essential behavioral characteristics.
3Measurement precision
If SPICE or fast-Spice is used, then analog device analysis is performed, but test bench size increases exponentially
Solution Approach 1:
The patent extracts analog devices from the complete circuit schematic and analyzes them separately to determine their small-signal parameters. By taking out the analog devices and representing them as equivalent digital models with extracted parameters, the method avoids the need for exhaustive test benches while maintaining analysis accuracy for the analog portions.
Solution Approach 2:
The patent creates simplified copies of analog devices in the form of equivalent digital models. These copies retain the essential small-signal characteristics (gain, bandwidth, impedance) of the original analog devices but can be processed efficiently by digital simulation tools, avoiding the exponential complexity of full SPICE test benches.
Data Source
AI summary
In a computer simulation of an analog device in a digital circuit, a piece-wise linear lookup table is used to determine the channel resistance of the transistors in the analog device, allowing the node voltages to take on non-digital values. The piece-wise linear lookup table contains a set of channel resistances corresponding respectively to gate-to-source voltages. The program uses multi-terminal binary decision graphs (MTBDDs) to represent non-digital resistances, capacitances and voltages in the circuit as a function of symbolic inputs. The program can analyze circuits containing more than two voltage sources by modeling voltage sources with voltage dividers between the maximum and minimum voltages in the circuit.