z where c is the capacitance of capacitor 420 u03c9 is the signal frequency of either v in or v ref and z is the small signal impedance of current source 406 the voltage comparator behaves similarly to the amplifier of fig2 in particular the circuits of fig4 and 2 have identical dc voltage gains and consequently the presence of capacitor 402 does not cause overshoot or undershoot in the frequency characteristics of the voltage gains a in and a ref for the voltage comparator of fig2 at high frequency operation u03c9c gt gt 1 z the voltage comparator of fig4 behaves very differently from that of fig2 for the input voltage gain a in a high frequency equivalent circuit for the voltage comparator of fig4 is provided in fig5 where corresponding transistors in fig4 and 5 are labeled accordingly the bias voltage v bias is the gate and drain voltage of pmosfet 414 at high frequencies v bias may be considered constant because as discussed earlier v ref is held constant when considering the voltage gain a in and capacitor 420 provides a high frequency short circuit to rail 424 the circuit of fig5 is seen to be a simple single stage common source amplifier at high frequency operation device parasitic capacitance causes a reduction in voltage gain a in for.