| 摘要 |
<p>A quadrature demodulator for suppressing noise affections as much as possible even when the level of a received signal becomes small, thereby reducing the occurrences of erroneous reproduction of the received data. In the quadrature demodulator, an I-signal and a Q-signal are generated from a modulated received signal, a local signal and from a local signal having been phase-shifted by 90 degrees, and then the DC components of the I-signal and Q-signal are removed by capacitors (37,38). In addition, the frequency components higher than the frequencies of the I-signal and Q-signal are removed by lowpass filters (35,36). The I-signal having passed through the lowpass filter is squared by an I-signal squaring part (43), while the Q-signal having passed through the lowpass filter is squared by a Q-signal squaring part (44). The squared I-signal and Q-signal are then added together by an adding part (45). A comparator (18) then compares the level of a resultant added signal (S1) with a threshold value (T1), thereby providing a signal (S2). A data generating part (48) of a digital signal processing part (12) inverts the signal level in response to each rising edge of the signal (S2), thereby demodulating the received data.</p> |
