Patent ID: 7898449

Claim:
A telescopic differential operational amplifier circuit for use in a pipelined A/D converter that operates during a sampling phase and a hold phase, the differential operational amplifier circuit including two auxiliary differential amplifiers connected to two cascode circuits, each cascode circuit being configured to include cascode-connected first to fourth transistors, the differential operational amplifier circuit comprising: an input terminal of the differential operational amplifier circuit, the input terminal being connected to a gate of the first transistor and a gate of the second transistor via first and second coupling capacitors, respectively, in each of the cascode circuits; an output terminal of the differential operational amplifier circuit, the output terminal connected to a connecting point of cascode-connected third and fourth transistors in each of the cascode circuits; a first switch connected to a connecting point of a gate of the first transistor and the first coupling capacitor in each of the cascode circuits; and a second switch connected to a connecting point of a gate of the fourth transistor and the second coupling capacitor in each of the cascode circuits, wherein, during the sampling phase, the first and second switches are turned on to apply a predetermined bias voltage to the gates of the first and fourth transistors, and the input terminal of the differential operational amplifier circuit is set to a common mode voltage, and wherein, during the hold phase, the first and second switches are turned off so that a voltage of each of the gates of the first and fourth transistors change to follow an input signal inputted via the input terminal with the coupling capacitor operating as a level shifter of the input signal, whereby the differential operational amplifier circuit performs push-pull operation that is operative only in a transconductance drive region and prevented from operating in a sieving region.