| 摘要 |
<p>PURPOSE:To extract stable timing where malfunction is small by providing an automatic gain control (AGC) circuit behind a specific band-pass filter which extracts 1/2 Nyquist frequency components as to the rear part and imaginary part of a demodulated signal wave in complex representation. CONSTITUTION:A fixed equalizer 12 removes the non-time-like distortion of a circuit. A timing extracting circuit 14 extracts the 1/2 Nyquist frequency components of the real and imaginary parts of the demodulated signal wave in complex representation by passing it through specific band-pass filters 1r and 1i and sends them out to product circuits 27r and 27i of AGC circuits 2r and 2i. The product circuits 27r and 27i feeds back a specific numeral obtained according to the output result of a sum circuit 4 to the demodulated signal wave passed through the specific band-pass filters 1r and 1i to perform multiplication, thereby holding the signal levels of the real and imaginary parts of the demodulated signal constant. Consequently, even a high-speed modem of, for example, about 19.2 kbps can use AGC circuits which have dynamics ranges of about 24 bits and are easily manufactured and realized.</p> |
