Electrical circuit means for detecting the frequency of input signals

• US 4,024,414 A
• Filed: 05/10/1976
• Issued: 05/17/1977
• Est. Priority Date: 10/31/1973
• Status: Expired due to Term

• Current Assignee: Consumer Microcircuits Limited
• Original Assignee: Bertram Frederick Mccarthy
• Inventors: Gurry, George W.
• Primary Examiner(s): Chatmon, Jr., Saxfield
• Application Number:
  US05/684,898
• Time in Patent Office: 372 Days
• Field of Search: 307/233, 307/232, 328/138, 328/136, 328/140, 328/151
• US Class Current: 327/45
• CPC Class Codes: G01R 23/15 Indicating that frequency of pulses is either above or below a predetermined value or within or outside a predetermined range of values, by making use of non-linear or digital elements (indicating that pulse width is above or below a certain limit)
• CPC Class Codes: H03D 1/2272 using FET's H03D1/2209, H03D1/2245 and H03D1/2281 take precedence

Abstract

A device for detecting input signals whose frequency lies within a predetermined range of frequencies. Included in the device is an oscillator and two sampling circuits which are operated by switching signals derived from the oscillator. An input signal of unknown frequency is applied to a first sampling circuit, an "oscillator sampling circuit" which generates a control voltage if the frequency of the input signal is within the range. The control voltage is applied to the oscillator and causes the frequency of the switching signals to become equal to a multiple of the frequency of the input signal. Further switching signals, also having a frequency equal to a multiple of the frequency of the input signal, are applied to the second sampling circuit, the "word sampling circuit", which also receives the input signal. The word sampling circuit then provides an output if the amplitude of the input signal is above a predetermined threshold value.

Claims

1. 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.

2. An electrical circuit as claimed in claim 1, wherein said oscillator means comprises oscillator means for producing first switching signals having a frequency initially equal to twice the frequency of an input signal within the predetermined range and variable over a range whose upper and lower frequencies are respectively equal to twice the upper and lower frequencies of the predetermined range and for centering each of the first sampling periods, which extend over an interval of time when the frequency of the first sampling periods has been caused to change to a value equal to twice the frequency of the instant input signal, on an instant of time substantially at an instant at which polarity of the instant input signal changes.

3. An electrical circuit as claimed in claim 2, wherein said oscillator means comprises oscillator means for extending each of the first sampling periods over an interval of time which is twice as long as the interval of time between successive first sampling periods.

4. An electrical circuit as claimed in claim 3, wherein said oscillator means comprises oscillator means for establishing the second sampling period as having a frequency which is initially equal to twice the frequency in the predetermined range and variable over a range whose upper and lower frequencies are respectively equal to twice the upper and lower frequencies of the predetermined range.

5. An electrical circuit as claimed in claim 4, wherein said oscillator means comprises oscillator means for extending each of the second sampling periods over an interval of time which is twice as long as the interval of time between successive second sampling periods.

6. An electrical circuit as claimed in claim 5, wherein said oscillator means comprises oscillator means for beginning and ending of the second sampling periods within a single half cycle of the instant input signal whenever the frequency of the second sampling periods has been caused to change to a value equal to twice the frequency of the instant input signal.

7. An electrical circuit as claimed in claim 6, wherein said oscillator means comprises oscillator means for commencing each of the second sampling periods at the instant at which polarity of the instant input signal changes sign.

8. An electrical circuit as claimed in claim 1, wherein said first sampling means comprises integrating storage means and switch means through which, in operation, the input signal is applied to said storage means, the first switching signals from said oscillator means being applied to a switching input of said switch means for causing in response thereto the input signal to be applied to said storage means for the duration of each switching signal.

9. An electrical circuit as claimed in claim 8, wherein said storage means in said first sampling means includes capacitor means upon which a charge representative of a difference in frequency and phase between the switching signals and the instant input signal is built up.

10. An electrical circuit as claimed in claim 9, wherein said integrating storage means comprises a resistor and capacitors to which the input signal is applied alternately.

11. An electrical circuit as claimed in claim 1, further including a differential amplifier, wherein said first sampling means comprises a resistor, two capacitors, and switch means through which the input signal is applied alternately to respective capacitors, and wherein each of said capacitors is connected to a respective input of said differential amplifier, said amplifier generating a control voltage which is applied to said oscillator means and causes a change in frequency of the first switching signals to a value at which each first sampling period is centered substantially at an instant of time at which polarity of the instant input signal changes, the charges on said capacitors being equal to each other.

12. An electrical circuit as claimed in claim 11, further including a switch, wherein output of said differential amplifier is coupled to said oscillator means via said switch, a switching signal being applied to said switch from said oscillator means for closing the switch only during intervals between the first sampling periods, and capacitor means provided at input connection to said oscillator means for providing the control voltage to said oscillator means which is unaffected by temporary fluctuations in charges on said two capacitors.

13. An electrical circuit as claimed in claim 1, wherein said second sampling means comprises integrating storage means and switch means through which the input signal is applied to said storage means, the second switching signals from said oscillator means being applied to a switching input of said switch means for causing the input signal to be applied to said storage means for the duration of each second switching signal.

14. An electrical circuit as claimed in claim 13, wherein said integrating storage means in the second sampling means includes capacitor means upon which charge representative of magnitude of the instant input signal is built up when the second sampling periods are brought into the further predetermined frequency and phase relationship with the input signal.

15. An electrical circuit as claimed in claim 14, wherein said integrating storage means comprises a resistor and first and second capacitors to which the second switching signals are applied alternately.

16. An electrical circuit as claimed in claim 1, further including a comparator and wherein said second sampling means comprises a resistor, two capacitors, and switch means through which the instant input signal is applied alternately to respective capacitors, each of said capacitors being connected to a respective input of said comparator, said comparator providing an output signal representing detection of an input signal when the difference between charges on said capacitors and hence the voltages applied to said comparator, exceeds a predetermined value and has a predetermined sign.

17. An electrical circuit as claimed in claim 16, including a counter connected to an output of said comparator, output of said counter assuming a predetermined condition representing detection of an input signal only when an output signal from the comparator has been maintained for a predetermined number of sampling periods.

18. An electrical circuit as claimed in claim 17, further including further switch means provided between said capacitors and said comparator, said further switch means being operated by an output voltage from said counter for effecting a reduction in predetermined magnitude of voltage below which voltage from said capacitors must fall before an output signal from said comparator is terminated.

19. An electrical circuit as claimed in claim 1, wherein said oscillator means comprises oscillator means for establishing initially a frequency of the first sampling periods equal to twice the frequency within the predetermined range and variable over a range whose upper and lower frequencies are respectively equal to twice the upper and lower frequencies of the predetermined range, each of the first sampling periods extending over an interval of time which, when the frequency of the first sampling periods has been changed to a value equal to twice the frequency of the instant input signal, equals one third of a cycle of the input signal and is substantially centered on a point on the input signal which has zero slope and each of the second sampling periods extends over an interval of time equal to one sixth of a cycle of the instant input signal and occupies the time between successive first sampling periods.