PLL System Behavior Simulation on Transistor Level

[teem]

Hi,

We generally simulate PLL system behavior and calculate loop parameters first by using tools like MATLAB or others, then start to realize the circuits. After that, we check the step response or phase noise on transistor level of the PLL with tools like HSpice or Spectre.

Here are my questions:

1. MATLAB simulation is based on linear model, but transistors are nonlinear elements. Is it possible to draw bode plot on transistor level to verify the results from MATLAB?​

2. If yes, how to do with HSpice or Spectre?​

3. PLL to do transient simulation with HSpice is time consuming. Are there better tools to do instead?​

Thanks in advance.

 

[crutschow]

1. All bode plot (AC) simulations are based upon linear models in the frequency domain, both in MATLAB and Spice simulators. A transistor level simulation in Spice is done in the time domain, so you would have to generate a plot from data generated from single frequency simulations at different frequencies of interest.

2. Not that familiar with Spectre but I suspect it makes little difference.

3. Transient simulations of circuits that have high frequency carrier with a low frequency feedback loop (such as a PLL or Switching Power Supplies) take a long time to settle because of the many thousand of cycles of the carrier needed for the loop to stabilize and reach a steady output. Generally the only way to speed that up is a faster computer or a simulation program designed to efficiently run on a multi-processor computer. Reducing the simulation accuracy parameters may increase the speed some but at the expense of accuracy.

 

[helpmejerry]

Spectre and spice offer additional simulation like pss etc. The first example in google of PSS anylysis for PLL https://www.cadence.com/rl/Resources/conference_papers/ctp_cdnlivesv2007_Thibieroz.pdf

Hope this helps.

BR Jerry