Class AB folded-cascode amplifier having cascode compensation
View Patent ↗A class AB folded-cascode amplifier having improved gain-bandwidth product, comprises a differential input circuit including a differential transistor pair coupled to a source of tail current and responsive to a differential input signal for conducting a first current, a cascode circuit coupled to the differential input circuit for supplying a second current thereto, and a class AB output stage. A compensation circuit is configured for feeding back mutually complementary compensation signals from an output node to the differential input circuit.
1. A class AB folded-cascode amplifier having improved gain-bandwidth product, comprising:
a differential input circuit including a differential transistor pair coupled to a source of tail current and responsive to a differential input signal for conducting a first current;
a cascode circuit coupled to the differential input circuit for supplying a second current thereto;
a class AB output stage; and
a compensation circuit configured for feeding back mutually complementary compensation signals from the output stage to the differential input circuit, wherein
the differential input circuit has mutually complementary sides,
the compensation circuit comprises a first feedback path without signal inversion from the output stage to one side of the differential input circuit, and a second feedback path with signal inversion from the output stage to the complementary side of the differential input circuit, and
the cascode circuit includes a first current mirror, and the second feedback path includes a second current mirror for inverting the output signal.
2. The class AB folded-cascode amplifier as recited in claim 1 , including a first capacitor for coupling from the output stage to the second current mirror and a second capacitor for coupling the inverted signal from the second current mirror to the complementary side of the differential input circuit.
3. A method of compensating a class AB folded-cascode amplifier of a type having a differential input circuit including a differential transistor pair coupled to a source of tail current and responsive to a differential input signal for conducing a first current, a cascode circuit coupled to the differential input circuit for supplying a second current thereto, and a class AB output stage, the method comprising the step of coupling mutually complementary signals from the output stage to the input differential circuit, wherein
the cascode circuit includes a current mirror,
the step of coupling includes implementing an inversion circuit external to the current mirror for inverting the compensation from the output stage, and
the inversion circuit comprises an additional current mirror.