Inverter models of CMOS gates for supply current and delay evaluation

The subject of this paper is the reduction of transistor-level models of CMOS logic gates to equivalent inverters, for the purpose of computing the supply current in digital circuits. No restrictions are applied to either the number of switching inputs or the transition times and relative delays of the input voltages. The relative positions of the switching inputs are also accounted for in the case of series-connected MOSFET's. When combined with our previously reported CMOS inverter model, the peak current is obtained in a time approximately three orders faster than HSPICE with the level-3 MOSFET model. The corresponding accuracy is around 12%. If the current waveform is required, the speed improvement is about an order less. Since the inverter model also yields the delay at no extra cost, the timing of the current waveforms can be done automatically, without recourse to a timing simulator. Although the emphasis here is on CMOS static gates, the method is applicable to dynamic logic gates as well.<
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