Filter which tracks changing frequency of input signal
AssigneeRCA Corporation
InventorEldon M. Sutphin, Jr.
Life of this patent
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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 rectangular voltage waveform which is derived from the output signal passed by the filter. The filter 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 an oscillator during each respective period. The time-representing count is inverted to a frequency-representing count which controls the duty cycle of a rectangular wave used to make the filter track the changing frequency of the input signal.
Claims6
A tracking filter, comprising
- a duty-cycle-controlled variable-frequency band-pass filter having a signal input terminal receptive to an electrical signal having many frequency components and having a signal output terminal for a selected frequency component which varies in frequency in direct proportion with engine speed, and having a frequency control input terminal,
- a frequency-to-duty-cycle converter coupled to said output terminal and operative repeatedly to translate each period of said selected frequency component to a rectangular wave having a duty cycle proportional to the frequency of said selected frequency component, and
- means to apply said rectangular wave to the control input terminal of said duty-cycle-controlled filter, whereby the filter tracks changes in the frequency of the selected frequency component passed by the filter.
Dependencies are inferred from the claim text.