Electrical circuit means for detecting the frequency of input signals

An electrical circuit for detecting input signals having a frequency which lies within a predetermined range of frequencies, the circuit comprising:

• first sampling means having a first input means and a switching input means;
• second sampling means having a first input means and a switching input means;
• means for applying same input signals to each of said first input means of said first and second sampling means;
• oscillator means having a control signal input means, first output means and second output means for generating in operation first switching signals at its said first output means and second switching signals at its said second output means, these first and second switching signals each having a given frequency which bears a predetermined relationship with a current input signal having a frequency within the predetermined range of frequencies;
• means for applying the first switching signals from said oscillator means to said switching input means of said first sampling means, said first sampling means being responsive in operation to an input signal applied to said first input means thereof and the first switching signals applied to said switching input means thereof for admitting an input signal thereto for first sampling periods whose frequency has a predetermined relationship with the given frequency and is within the predetermined range of frequencies and for generating a control signal representing at least one of (1) a difference between the given frequency and frequency of the current input signal being received and (2) a departure from a predetermined phase relationship between the first sampling periods and the current input signal;
• means for applying the control signal from said first sampling means to said control input means of said oscillator means, said oscillator means being responsive to a control signal representative of an input signal having a frequency within the predetermined range to cause first sampling periods of the first switching signals to have a predetermined frequency and phase relationship with the current input signal and for causing second sampling periods of the second switching signals to have a further predetermined frequency and phase relationship with the current input signal;
• and
• means for applying the second switching signals to said switching input means of said second sampling means, said second sampling means being responsive in operation to signals from said oscillator second output means establishing the second sampling periods having the further predetermined frequency and phase relationship to the current input signal and responsive to the input signal being above a predetermined value for generating an output signal from said second sampling means representing detection of an input signal within the predetermined range of frequencies.