Patent ID: 7187235
Filing Date: 2007-03-06
Classification: H03F

Abstract:
1. A rail-to-rail operational amplifier comprising: a differential input stage circuit including a first differential amplifier and a second differential amplifier, the first differential amplifier coupled to a negative supply rail voltage via a first current source, the second differential amplifier coupled to a positive supply rail voltage via a second current source; a current summing circuit including a current mirror circuit, a third current source and a fourth current source, the current summing circuit being coupled between the positive and negative supply rail voltages and receiving an output signal of the differential input stage circuit; an output stage circuit coupled to output terminals of the current summing circuit to output a differential amplified signal, the output stage circuit being coupled between the positive and negative supply rail voltages; and a bias control circuit coupled to the output terminals of the current summing circuit and coupled between the current mirror circuit and the fourth current source, the bias control circuit receiving at least one bias control transistor bias voltage and at least one bias control transistor control voltage to control a bias voltage of input terminals of the output stage circuit, and to control a bias current of the output stage circuit; wherein the bias control circuit includes a first bias control circuit and a second bias control circuit, the first bias control circuit being coupled in parallel to the second bias control circuit between the current mirror circuit and the fourth current source, the first bias control circuit including a first bias control transistor and a second bias control transistor, a control electrode of the first bias control transistor receiving a first bias control transistor bias voltage, and a control electrode of the second bias control transistor receiving a first bias control transistor control voltage.