Patent ID: 8229032

Claim:
A signal receiver comprising: a receiving circuit that receives a differential signal via a transmission line, which includes a pair of signal wires for transmitting the differential signal; and an impedance control circuit that controls an input impedance so as to reduce a common mode noise, wherein the impedance control circuit includes a detection element for detecting at least one of a voltage, a current and an electric power of the common mode noise, and wherein the impedance control circuit controls the input impedance in accordance with change of the at least one of the voltage, the current and the electric power of the common mode noise, wherein the detection element includes a pair of resistors, which are coupled in series with each other between the pair of signal wires, wherein the impedance control circuit further includes a positive side impedance element and a positive side switching element, which are coupled between the transmission line and a ground, wherein the impedance control circuit further includes a positive side comparator for comparing the voltage of the common mode noise with a positive side threshold voltage, which is defined by adding a predetermined margin voltage to a direct-current voltage between the transmission line and the ground, wherein the positive side switching element turns on when the voltage of the common mode noise exceeds the positive side threshold voltage, wherein the impedance control circuit further includes a negative side impedance element and a negative side switching element, which are coupled between the transmission line and the ground, wherein the impedance control circuit further includes a negative side comparator for comparing the voltage of the common mode noise with a negative side threshold voltage, which is defined by subtracting a predetermined margin voltage from a direct-current voltage between the transmission line and the ground, and wherein the negative side switching element turns on when the voltage of the common mode noise falls below the negative side threshold voltage.