Weak Undriven State Modeling for RTL Power Verification
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Solution Overview
Problem
Conventional circuit simulators fail to differentiate between a powered-up circuit element with an unknown output value and a powered-down circuit element, leading to inaccurate modeling of weak undriven states, which is crucial for complex power management scenarios and power-managed integrated circuits.
Innovation Solution
Introducing a 'weak' undriven state as a signal state, distinct from the conventional unknown state, allowing digital event-driven circuit simulators to model and verify designs with circuits resilient to weak undriven states, avoiding the need for electrical simulators like SPICE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional unknown state is used to represent both powered-up and powered-down circuit elements, then the simulation model is simple, but the accuracy of power management verification deteriorates
Solution Approach 1:
The conventional unknown state is segmented into two distinct states: a strong unknown state (X) for powered-up circuit elements and a weak unknown state (WX) for powered-down circuit elements. This segmentation allows the simulation model to differentiate between powered and unpowered elements, enabling accurate verification of power management scenarios while maintaining event-driven simulation efficiency.
2Measurement precision
If electrical simulators like SPICE are used to accurately model weak undriven states, then the accuracy of electrical behavior simulation is improved, but the simulation time and computational resources increase significantly
Solution Approach 1:
The patent replaces the continuous electrical simulation approach (SPICE) with a discrete event-driven simulation approach. By introducing the weak unknown state (WX) with defined Boolean logic behavior, the system substitutes heavy electrical simulation mechanics with lighter logical abstraction mechanics, achieving adequate accuracy for power management verification without the computational burden of full electrical simulation.
3Productivity
If conventional Boolean logic abstraction is used for circuit simulation, then the simulation speed is high, but the ability to model undriven floating states deteriorates
Solution Approach 1:
The patent extends the conventional Boolean logic parameter set by introducing a new state parameter (WX - weak unknown) with specific logical behavior rules. This parameter change enables the simulation to model undriven floating states and powered-down element behavior while maintaining the speed advantages of event-driven Boolean logic simulation.
Data Source
AI summary
A “weak” undriven state is defined as a signal state, distinguished from conventional unknown and high impedance states, and methods of representing this “weak” undriven state in circuit modelling and power aware digital/mixed-signal simulations for comprehensive and complete RTL-level design verification. The conventional unknown state refers to a circuit element that is powered but has an unknown value, a circuit element that is not powered, or a circuit element having an undriven, floating signal. The unknown state is modified, and the “weak” undriven state refers to a circuit element that is not powered and has an unknown value. The “weak” undriven state can have an electrically high impedance to known supply or ground when no other circuit element is active. The “weak” undriven state distinction is particularly useful to model and verify circuit designs known to be resilient to “weak” undriven states, using event driven logic circuit simulators.