It disables an error message in Spectre that would prevent the model from being used in SpectreRF. SpectreRF cannot handle hidden state if that state affects the behavior of the model. Spectre has a way of examining the model to determine if it contains hidden state, but it is not sophisticated enough to determine if that state affects the behavior of the model. By adding the instrument_module attribute, you are saying any hidden state the model contains is innocuous.

Other that that it in no way affects the behavior of the model, and you can feel free eliminating it if you do not plan to use the model in SpectreRF.

-Ken

I cannot process that last sentence. Is it a question?

-Ken

SpectreRF is a collection of new analysis that are available in Spectre. They are very powerful and very useful. They were originally targeted for RF circuits but their capabilities are general and they have found wide applicability in analog, mixed-signal and even digital circuits.

Perhaps aspect of the RF analyses of SpectreRF that is the most important is that they extend the small-signal analyses (AC and noise primarily) to periodically driven circuits. All of the circuits you mentioned are periodically driven and so benefit from RF analysis. For example, SpectreRFs' PNoise analysis allows you to predict the noise performance of both the components that make up a PLL (oscillator, pfd/cp, divider, etc.) as well as the PLL itself. As another example, people are now using the Pstability analysis to determine whether switch-mode power supplies are stable. If you browse the Analysis section of this website you will find several application notes that describe how to apply SpectreRF to traditional analog and RF circuits.

-Ken