A Novel Frequency Measurement Methodology for Clock Synchronization in SPICE-Based Simulators

Nowadays, there is an increasing demand for complex behavioral models on the market, as simulation has become the main verification approach used for both analog and digital functionalities. One of the most popular mixed-signal simulators nowadays is Simulation Program for Integrated Circuits Emphasis (SPICE). Over the last decade, the digital part in circuits has become predominant, but this poses big challenges when developing SPICE simulation models, as the circuits are synchronized upon internal or external clock signals, where the frequency accuracy is mandatory. The existing SPICE based simulators have built-in options to measure the signal frequency and duty cycle, but only after the simulation has completed, and in this way the frequency information can not be used during the simulation to synchronize the clock signals. There is a lot of research on frequency measurement techniques in the literature, but this topic has not been translated and covered in SPICE until now. Implementing the physical frequency measurement circuits proposed previously in the literature would increase the models’ complexity and the simulation time, without benefitting the final user. For this reason, in this article, a novel frequency measurement methodology for clock synchronization in SPICE based simulators is proposed, which aims to provide accurate measured frequency and duty cycle values for the digital clock signals with a fast simulation time. The performance evaluation of this methodology is done using OrCAD Capture, which is the most popular SPICE-based simulation environment.