Patent ID: 9685914
Date: 2017-06-20
CPC Classifications: H03F

Claim:
1. An amplifier circuit comprising: a differential pair including a pair of a first transistor and a second transistor, wherein each of the first transistor and the second transistor is a transistor in which, in response to a voltage between a control terminal and a first terminal, a current flowing between the first terminal and a second terminal is controlled, and a differential signal is input to a pair of the control terminals included in the pair of the first transistor and the second transistor; a load circuit configured to generate a differential signal corresponding to currents flowing through a pair of the second terminals included in the pair of the first transistor and the second transistor in the differential pair; an output amplifier stage configured to amplify and output the differential signal generated by the load circuit; a feedback circuit configured to feed the differential signal output by the output amplifier stage back to a pair of the first terminals included in the pair of the first transistor and the second transistor in the differential pair; a first chopping circuit configured to shift, to a frequency band on a high frequency side, frequency components of the differential signal input to the pair of the control terminals in the differential pair by repeatedly inverting polarity of the differential signal; a second chopping circuit configured to bring, back to an original frequency band from the frequency band on the high frequency side, frequency components of the differential signal input to the output amplifier stage by repeatedly inverting, in synchronization with the polarity inversion operation of the first chopping circuit, polarity of the differential signal; and a third chopping circuit configured to shift, to the frequency band on the high frequency side, frequency components of the differential signal fed back to the pair of the first terminals of the differential pair by the feedback circuit by repeatedly inverting, in synchronization with the polarity inversion operation of the first chopping circuit, polarity of the differential signal; and wherein the output amplifier stage has a low-pass filter characteristic for attenuating frequency components due to the polarity inversion operation in the first chopping circuit.