Patent ID: 7218685

Claim:
A direct conversion receiver which comprises: a local oscillator which oscillates a carrier wave at a reception frequency plus an offset; a first multiplier which multiplies a reception signal by an output of the local oscillator; a first low pass filter which rejects a double wave from an output of the first multiplier; a first AD converter which converts an output of the first low pass filter into a digital signal to provide an in-phase component of the digital signal; a first 90° phase shifter which shifts the output of the local oscillator by 90°; a second multiplier which multiplies the reception signal by an output of the first 90° phase shifter; a second low pass filter which reject the double wave from an output of the second multiplier; a second AD converter which converts an output of the second low pass filter into the digital signal to provide a quadrature component of the digital signal; and a digital signal processing section which performs processing for receiving the in-phase component of the digital signal and the quadrature component of the digital signal to reject an image frequency signal contained in these received signals and which performs frequency conversion processing for removing the offset provided at the local oscillator; wherein the digital signal processing section comprises: a second 90° phase shifter which receives the quadrature component of the digital signal output from the second AD converter and which performs 90° phase shift processing; a delay circuit which receives the in-phase component of the digital signal output from the first AD converter to output it with the same delay time as a delay time in the second 90° phase shifter; and an adder which performs addition or subtraction between an output of the second 90° phase shifter and an output of the delay circuit.