Input frequency, digital circuits

HCT and ACT parts include an additional static power dissipation term proportional to the number of TTL inputs begin driven nAIddVdd> where AIdd is specified by the manufacturer). CMOS average power consumption is proportional to the frequency of operation, whereas power consumption of TTL circuits is almost independent of operating frequency until about 1 MHz, when dynamic power dissipation becomes significant (see Fig. 8.37). Direct comparison of CMOS and TTL power consumption for a digital system is difficult, since not all outputs are changing at the same frequency. Moreover, the relative... 

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