Modeling digital substrate noise injection in mixed-signal IC's

Techniques are presented to compactly represent substrate noise currents injected by digital networks. Using device-level simulation, every gate in a given library is modeled by means of the signal waveform it injects into the substrate, depending on its input transition scheme. For a given sequence of input vectors, the switching activity of every node in the Boolean network is computed. Assuming that technology mapping has been performed, each node corresponds to a gate in the library, hence, to a specific injection waveform. The noise contribution of each node is computed by convolving its switching activity with the associated injection waveforms. The total injected noise for the digital block is then obtained by summing all the noise contributions in the circuit. The resulting injected noise can be viewed as a random process, whose power spectrum is computed using standard signal processing techniques. A study was performed on a number of standard benchmark circuits to verify the validity of the assumptions and to measure the accuracy of the obtained power spectra.