Re: about op amp
In analog circuits, the power dissipated by a one pole system is
P=8(Vdd/Vpp)kTf(S/N)
The minimum power consumption of analog circuits at a given temperature is basically set by the required SNR and the frequency of operation. Since this minimum power consumption is also proportional to the ratio between the supply voltage and the signal peak-to-peak amplitude, power efficient analog circuits should be designed to maximize the voltage swing. Hence it is desirable to have a rail to rail output stage in low power amplifier design