Demodulator for frequency modulated signal accompanied by reference signal
AssigneeEMI Limited
InventorAlan Robson
Life of this patent
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Abstract
The demodulator is especially adapted for a data signal (F'c) that was recorded on tape in the form of a frequency modulated signal together with a reference signal (F'R) of frequency greater than the greatest frequency of the data signal, so that both signals are subject to the same proportional frequency errors. During each cycle of the data signal, a representation of the period of one cycle of the reference signal is measured and stored. Then at the end of each following cycle of the data signal, there is produced a pulse of area dependent on the representation. A filter (LPF) produces a signal representing the area of each pulse averaged over one cycle of the data signal.
Claims8
A frequency demodulator for demodulating a frequency modulated signal derived from a source where it is accompanied by a reference signal of frequency greater than the greatest frequency of the modulated signal, the modulated and reference signals being subject to the same proportional frequency errors,
- the demodulator comprising
- an input for receiving the modulated signal,
- an input for receiving the reference signal,
- means arranged to measure and store, during each cycle of the modulated signal, a representation of the period of one cycle of the reference signal occurring during that cycle of the modulated signal,
- means responsive to the modulated signal to produce a pulse of area dependent on the stored representation during a predetermined portion of the cycle of the modulated signal following the one in which the representation was stored, and
- filter means for producing a signal representing the area of each pulse averaged over one cycle of the modulated signal.
Dependencies are inferred from the claim text.