Which CMOS gate network in Fig Q14 can operate at the highes

Which CMOS gate network in Fig. Q14 can operate at the highest frequency? Explain your answer

Solution

When more load gate inputs are added to the driving gate output, the total capacitance increases because the input capacitances effectively appear in parallel. This increase in capacitance increases the charging and discharging times, thus reducing the maximum frequency at which the gate can be operated. Therefore, the fan-out of a CMOS gate depends on the frequency of operation. The fewer the load gate inputs, the greater the maximum frequency.

for (a)

number of load gate inputs=6

for (b)

number of load gate inputs=7

for (c)

number of load gate inputs=8

so here for (a) has 6 load gate inputs so it operate at high frequency.