Patent ID: 8218688
Filing Date: 2012-07-10
Classification: H03D,H04B

Abstract:
1. A quadrature demodulator which mixes a two-level-form modulated reception signal with a local signal to generate an in-phase signal (I-signal), mixes the reception signal with the local signal having a phase shifted through 90 degrees to generate a quadrature signal (Q-signal), and generates binary data from the I-signal and the Q-signal, the quadrature demodulator comprising: an I-signal direct current (DC) component removing section which removes a DC component from the I-signal; an I-signal low-pass filter which removes a frequency component which is higher than a frequency of the I-signal; an I-signal squaring section which squares the I-signal having passed through the I-signal DC component removing section and the I-signal low-pass filter; a Q-signal DC component removing section which removes a DC component from the Q-signal; a Q-signal low-pass filter which removes a frequency component which is higher than a frequency of the Q-signal; a Q-signal squaring section which squares the Q-signal having passed through the Q-signal DC component removing section and the Q-signal low-pass filter; an adding section which adds an output from the I-signal squaring section and an output from the Q-signal squaring section together; and a data generating section which generates two-level-form data whose signal level is inverted every time one of a rising edge and a falling edge occurs in the signal output by the adding section, wherein the rising edge and falling edge each pass a predetermined threshold; wherein an I-signal variable gain amplifier is provided before the I-signal squaring section, and a Q signal variable gain amplifier is provided before the Q-signal squaring section; and wherein the I-signal variable gain amplifier and the Q-signal variable gain amplifier control gains in accordance with an amplitude value of the signal output by the adding section.