To simulate the noise of an oscillator with a frequency divider, you combine them and treat the pair as an oscillator. The only real difference between simulating the oscillator alone and the oscillator with the divider is that the expected output frequency is specified to be N smaller when the divider is present, where N is the divide ratio of the divider. Also, the pair of nodes that Spectre monitors should be associated with the output of the divider so that Spectre is observing a signal with a strong component at the fundamental frequency.

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