Patent ID: 8963637
Filing Date: 2015-02-24
Classification: H03G

Abstract:
1. A semiconductor device comprising: a variable gain type differential amplifier circuit which receives a gain setting signal, amplifies differential input signals by a gain indicated by the gain setting signal, and outputs differential output signals; and a correcting circuit which cancels an offset voltage generated in the differential amplifier circuit; the correcting circuit cancelling the offset voltage by receiving the gain setting signal, generating a correction voltage charged in accordance with the gain, and adding the correction voltage to the differential output signals, wherein the correcting circuit includes a variable current source for correction connected to differential output nodes from which the differential output signals are outputted, and the variable current source for correction generates a correction current corresponding to the correction voltage by changing a predetermined reference current in proportion to the gain, and wherein the correcting circuit includes: a variable current source for reference which sets a current value of the reference current; a first reference transistor to which a current from the variable current source for reference is supplied; a first transistor, a second transistor, a first positive electrode switch, a second positive electrode switch, a first negative electrode switch, and a second negative electrode switch, which are included in the variable current source for correction; and a control circuit, and the first transistor configures a current mirror circuit with the first reference transistor so as to generate a first current, the second transistor configures a current mirror circuit with the first reference transistor so as to generate a second current, the first positive electrode switch and the second positive electrode switch connect the first current and the second current to respective positive electrodes of the differential output nodes, the first negative electrode switch and the second negative electrode switch connect the first current and the second current to respective negative electrodes of the differential output nodes, and, in accordance with change of the gain setting signal, the control circuit changes ON/OFF states of the first positive electrode switch and the second positive electrode switch in a state that both of the first negative electrode switch and the second negative electrode switch are controlled to be turned OFF, or changes ON/OFF states of the first negative electrode switch and the second negative electrode switch in a state that both of the first positive electrode switch and the second positive electrode switch are controlled to be turned OFF.