Modeling of digital substrate noise generation and experimental verification using a novel substrate noise sensor

Substrate coupling in mixed-signal ASICs can cause important performance degradation of the analog circuits. Accurate simulation is therefore needed to investigate the generation, propagation and impact of substrate noise. Recent studies have mainly concentrated on the time domain behavior of generated substrate noise and dealt mostly with noise injection from a single noise source. This paper will focus on the generation of substrate noise by digital circuits and on the spectral content of this noise. To simulate the noise generation a SPICE substrate model has been developed, which allows accurate simulation of substrate noise generated by small digital circuits. The correctness of this model has been verified with measurements of substrate noise on a test chip, using a novel wide-band, continuous-time substrate noise sensor, which allows accurate measurement of the spectral content of substrate noise. It is shown that the difference between spectral noise peaks and the noise floor can be up to 40 dB.