Patent ID: 7847599

Claim:
A start signal detection circuit comprising: a wave-detection circuit that outputs a voltage in accordance with an envelope of a radio signal from an output point, the radio signal being input from a detection point; a reference voltage generation circuit that outputs a voltage at the output point at a non-signal state as a reference voltage to a reference point; and a differential amplification circuit that amplifies and outputs a voltage difference between the output point and the reference point; wherein the wave-detection circuit comprises: a first diode having an anode connected to a power supply through a first current source and a cathode connected to the detection point; a second diode connected between the detection point and a ground; and a first capacitor connected between the anode of the first diode and an alternating ground; wherein the cathode of the first diode serves as the output point; and wherein the differential amplification circuit includes a differential pair composed of transistors that use charges as a carrier.