Filter which tracks changing frequency of input signal
First Claim
1. A band-pass filter having a pass band which tracks the changing frequency of an input signal, comprisinga voltage-controlled filter including a signal input terminal, a signal output terminal and a frequency control terminal,a trigger circuit connected to said signal output terminal to translate the sine wave passed through said filter to a pulse wave,a converter receptive to said pulse wave and operative repeatedly to translate the period between successive pulses to a frequency-representing voltage, andmeans to apply said frequency-representing voltage to the frequency control terminal of said voltage-controlled filter.
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Abstract
A tracking band-pass filter useful for locking onto, and passing, an input signal which changes rapidly in frequency. The filter has a frequency pass band controlled by a voltage which is derived from the output signal passed by the filter. The output signal is translated from a sine wave to a pulse wave. The period between each two successive pulses is measured by counting the cycles of a oscillator during each respective period. An inverter translates the time-representing count signal to a corresponding frequency-representing voltage which is applied to the filter to control its frequency pass band.
29 Citations
7 Claims
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1. A band-pass filter having a pass band which tracks the changing frequency of an input signal, comprising
a voltage-controlled filter including a signal input terminal, a signal output terminal and a frequency control terminal, a trigger circuit connected to said signal output terminal to translate the sine wave passed through said filter to a pulse wave, a converter receptive to said pulse wave and operative repeatedly to translate the period between successive pulses to a frequency-representing voltage, and means to apply said frequency-representing voltage to the frequency control terminal of said voltage-controlled filter.
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5. A band-pass filter having a pass band which tracks the changing frequency of an input signal, comprising
a voltage-controlled filter including a first voltage-controlled integrator coupled from a signal input terminal to a signal output terminal, a second voltage-controlled integrator and a constant-Q circuit coupled in parallel feedback paths from said output terminal to said input terminal, a trigger circuit connected to said output terminal to translate each cycle of the signal passed through said filter to a trigger pulse, a frequency-to-voltage converter including a constant-frequency oscillator and a counter coupled to count the cycles from the oscillator, means applying the output of said trigger circuit to reset said counter, a digital-to-analog converter to translate the maximum counts from said counter to a time-representing voltage reprsenting the time periods between successive trigger pulses, and inverter means to translate said time-representing voltage to a frequency-representing voltage, and means to apply said frequency-representing voltage to said first and second voltage-controlled integrators to control the frequency pass band of said filter.
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6. Means for determining the frequency or repetition rate of a pulse wave, comprising
a constant-frequency oscillator having a frequency much higher than the frequency of the pulse wave, a counter coupled to count the cycles from the oscillator, means employing each pulse of the pulse wave to reset said counter, and an inverter means to translate each time-representing count from the counter to a frequency-representing signal.
Specification