| 摘要 |
An FM detector circuit can simultaneously reduce noise in the bandwidth ratio, clip noise produced by reduction of the bandwidth and noise produced by tracking errors resulting from changes in the signal level. The FM detector circuit contains an AVR circuit (2) for making the input signal level constant, a tracking band pass filter (5) with a multilevel RF amplifier circuit (4) linked with the AGC circuit (2) for producing a requisite level of input signal, a variable capacitance diode linked with the amplifier circuit (4), where the filter has a variable central frequency and follows the FM signal from the amplifier circuit (4) for enlarging the apparent bandwidth of the input signal, and a PLL detector circuit (14) linked with the band pass filter (5). The detector circuit also contains a loop for amplification and feedback of the output signal from the PLL detector circuit (14) to the tracking band pass filter (5). |
