| 摘要 |
<p>A tracking filter has a tunable filter responsive to an input signal for producing a filtered output signal, a Hilbert transformer for producing an in-phase reference signal and a quadrature-phase reference signal from the filtered output signal, and a discriminator responsive to the input signal and the in-phase and quadrature-phase reference signals for producing a passband center frequency control signal and a passband width control signal for controlling the passband center frequency and the passband width of the tunable filter. The frequency discriminator performs complex demodulation of the input signal with the in-phase reference signals to produce respective in-phase and quadrature-phase baseband signals which are low-pass filtered. The quadrature-phase baseband signal is divided by the in-phase baseband signal. The quotient is integrated to produce the passband center frequency control signal. Preferably the baseband signals are also filtered by adjustable filters having passband center frequencies and passband widths controlled in response to the passband center frequency control signal and the passband width control signal, respectively. Preferably the tracking filter is a digital filter. <IMAGE></p> |
