Circuit for determining the difference between a fixed and unknown frequency

Claim 3

A method according to claim 1, wherein said step of generating said output signal comprises: delaying said difference signal by said predetermined number of cycles of said input signal to provide a delayed signal; and applying said difference and said delayed signals to a coincidence gate to form said output signal.

Claim 4

A method according to claim 1, wherein said step of forming said difference signal comprises sampling said standard signal once per cycle of said input signal and holding each sampled value until the next succeeding sample.

Claim 5

A method according to Claim 1, wherein the method further comprises the steps of: forming a second difference signal differing in phase from said first difference signal; and generating a second output signal from said second difference signal having a polarity dependent of the sense of the difference between the period of the input signal and the standard period.

Claim 6

Apparatus for determining the fractional difference in the period of an input signal from a standard period, the apparatus comprising: a generator for generating a standard signal having said standard period; an input terminal for receiving said input signal; a frequency subtractor connected to said generator and to said input terminal for forming a difference signal the frequency of which is equal to the difference between the frequencies of said input and standard signals; and output-signal-generating means connected to said frequency subtractor for generating from said difference signal a signal which is the output signal comprising a pulse the duration of which is equal to a predetermined number of cycles of said input signal for each cycle of said difference signal.

Claim 7

Apparatus for determining the fractional difference in the period of an input signal from a standard period, the apparatus comprising: a generator for generating a standard signal having said standard period; an input terminal for receiving said input signal; a frequency subtractor connected to said generator and to said input terminal for forming a difference signal the frequency of which is equal to the difference between the frequencies of said input and standard signals; and output-signal-generating means connected to said frequency subtractor for generating from said difference signal a signal which is the output signal comprising a pulse the duration of which is equal to a predetermined number of cycles of said input signal for each cycle of said difference signal.

Claim 8

Apparatus according to claim 5, wherein said output-signal-generating means comprises: a delay device connected to said frequency-subtractor to delay said difference signal by said predetermined number of cycles of said input signal to provide a delayed signal; and a coincidence gate connected to said frequency-subtractor and said delay device for forming the output signal.

Claim 9

Apparatus according to claim 6, wherein said output-signal-generating means additionally comprises: a second delay device connected in cascade with the first-mentioned delay device to provide a second delayed signal also delayed by a predetermined number of cycles of the input signal; a second coincidence gate connected to said frequency-subtractor and to said second delay device for forming a second output signal; and means connected to the first and second delay devices to select a desired one of the output signals.

Claim 10

Apparatus according to claim 5, wherein said frequency-subtractor comprises a clocked bistable, which, in use, samples said standard signal once per cycle of said input signal and holds each sampled value until the next succeeding sample.

Claim 11

Apparatus according to claim 5, further comprising: a second subtractor for forming a second difference signal differing in phase from said first difference signal; and switching means for switching the output signal in accordance with the polarity of said second difference signal in such a manner that the sense of the fractional difference in the period of the input signal is indicated.

Claim 12

Apparatus according to claim 7, wherein said frequency subtractor comprises a clocked bistable which, in use, samples said standard signal once per cycle of said input signal and holds each sample value until the next succeeding sample; and including; a second subtractor for forming a second difference signal differing in phase from said first difference signal; and switching means for switching the output signal in accordance with the polarity of said second difference signal in such manner that the sense of the fractional difference in the period of the input signal is indicated.