| 摘要 |
<p>1484253 Frequency detectors G W GURRY and B F MCCARTHY 30 Oct 1974 [31 Oct 1973] 50666/73 Heading H3A A circuit for detecting when an input signal lies within a predetermined frequency range and has an amplitude exceeding a predetermined value comprises sampling circuits 3, 5 to which the input signal is supplied and which are also fed with sampling signals #2A, #2B, #3A, #3B, from a voltage controlled oscillator circuit 1, the control signal for the oscillator being derived from the sampling circuit 3. This circuit samples the input signal about its zero crossings to provide an output proportional to frequency. As long as the frequency of the input signal lies within the range determined by high and low limit signals fed to oscillator VCO the signal derived from sampler 3 will lock the oscillator circuit to the frequency of the incoming signal. Sampling signals #3A, #3B are phase displaced from #2A, #2B and sampler 5 produces an output dependent on amplitude. When this amplitude exceeds a predetermined value, a signal is produced at the OUTPUT terminal of the circuit.</p> |
