Patent ID: 8319677
Filing Date: 2012-11-27
Classification: H03M

Abstract:
1. A semiconductor integrated circuit device having an A/D converter of a successive approximation type that performs sampling of an input signal and successive approximation to convert an analog signal to a digital signal, wherein the A/D converter comprises: a first switch whose one of coupling parts is coupled to an input part to which an analog signal for A/D conversion is inputted; a signal capacitance element whose one of coupling parts is coupled to the other coupling part of the first switch; a D/A converter that outputs an analog signal for conversion; a second switch coupled between an output part of the D/A converter and a coupling part between the first switch and the signal capacitance element; a differential amplifier having a first input part to which the other coupling part of the signal capacitance element is coupled and a second input part to which one of coupling parts of a reference capacitance element is coupled, and amplifying a differential voltage; and an impedance matching circuit that supplies a reference voltage for comparison to the second input part of the differential amplifier via the reference capacitance element, the impedance matching circuit configured to selectively provide a first impedance or a second impedance; wherein the impedance matching circuit comprises: a first impedance unit providing the first impedance for a time of sampling; and a second impedance unit providing the second impedance for a time of successive approximation, and wherein at the time of sampling, a reference voltage for comparison is supplied via the first impedance unit, and at the time of successive approximation, the reference voltage for comparison is supplied via the second impedance unit.