A comparison by simulation and by measurement of the substrate noise generated by CMOS, CSL, and CBL digital circuits

Current-steering logic (CSL) and current-balanced logic (CBL) are logic families that have been proposed with the objective of reducing the substrate noise in mixed-signal integrated circuits. These two families are compared here with conventional CMOS by simulation, using a substrate model extracted from the layouts, and also by measurements on a test chip. With small, low-power cells, noise reduction of CSL and CBL with respect to CMOS is only marginal; the same result is obtained with large, high-power (buffer) cells, if the supply wire inductance is very low. For large cells with typical wire bonding supply inductance (of the order of 10 nH), CBL cells provide significant noise reduction and are more effective than CSL cells; these become even noisier than CMOS cells for large inductance values. The results here, considering the real substrate noise, are more reliable than previous evaluations considering only the amplitude of the supply current spikes.