Patent ID: 8463225
Filing Date: 2013-06-11
Classification: H03D,H04B

Abstract:
1. A semiconductor integrated circuit comprising: an active low-pass filter having a filter processing function and an amplifying function; two calibration resistors coupled to differential output terminals of the active low-pass filter; a voltage comparator coupled to the differential output terminals of the active low-pass filter via the two calibration resistors; a control circuit that generates a digital control signal on the basis of an output signal of the voltage comparator and outputs the signal; a digital-to-analog converter that converts the digital control signal output from the control circuit into a calibration analog current and outputs the current; and a switch that switches coupling of an output terminal of the digital-to-analog converter between the two calibration resistors and differential input terminals of an operational amplifier in a first stage in the active low-pass filter, wherein in a calculation period of calculating the digital control signal for reducing the DC offset voltage between the differential output terminals of the active low-pass filter, the control circuit calculates the digital control signal by detecting calibration voltage between the two input terminals depending on voltage drop in at least one of the two calibration resistors caused by the calibration analog current flowing in an analog current output terminal of the digital-to-analog converter by the voltage comparator, and wherein in a calibration period of reducing the DC offset voltage after the calculation period, the calibration analog current as an output signal of the digital-to-analog converter responding to the digital control signal calculated by the control circuit flows in at least one of the differential input terminals of the operational amplifier in the first stage via the switch.