CIRCUIT AND METHOD FOR DEVELOPING SIGNAL INDICATIVE OF UNKNOWN FREQUENCY

• US 3,701,012 A
• Filed: 07/06/1970
• Issued: 10/24/1972
• Est. Priority Date: 07/06/1970
• Status: Expired due to Term

• Current Assignee: Motorola Solutions Canada, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Gordon R. Lang
• Inventors: Lang, Gordon R.
• Primary Examiner(s): Smith, Alfred E.
• Application Number:
  US05/052,472
• Time in Patent Office: 841 Days
• Field of Search: 324/79 328/140,134 329/124,122,50
• US Class Current: 324/76.43
• CPC Class Codes: G01R 23/00 Arrangements for measuring frequencies; Arrangements for analysing frequency spectra

Abstract

An unknown signal is mixed with a first reference signal and, in a separate mixing, with a second reference signal obtained by altering the phase of the first reference signal by pi /2 radians (where the signals are of the same frequency). The sum or the difference product of the first mixing is filtered out and the corresponding product of the second mixing is also filtered out; one of the two last-mentioned products is delayed relative to the other, and then the undelayed product and the delayed product are mixed while ensuring that the products mixed are of substantially constant amplitude.

Claims

1. The method of determining the frequency of a signal comprising:

performing a first mixing of said signal with a first reference signal;

performing a second mixing of said signal with a second reference signal obtained by altering the phase of said first reference signal by pi /2 radians;

where said reference signals are of the same frequency and differ in phase by pi /2 radians;

filtering from the products of said first mixing, a first product chosen from the class of products consisting of the sum and the difference of the mixed signals;

filtering from the class of products of said second mixing, a second product chosen from the class of products comprising the sum and the difference of the mixed signals, the choice being the same as for said first product;

delaying one of said filtered mixer products relative to the other by a delay Tau , delay Tau being chosen from the class of functions consisting of a constant or a function of frequency;

mixing in a third mixing step said delayed one mixer product and said other mixer product, while ensuring that the products mixed are of substantially constant amplitude.

2. The method as claimed in claim 1 wherein said filtering is performed so that the first product comprises the difference of the mixed signals, the second product comprises the difference of the mixed signals, and the output of the third mixing step is filtered to pass only signals of smaller frequency than a predetermined value.

3. The method as claimed in claim 1 wherein said filtering of the products from said first mixing is performed so tHat the first product comprises the sum of the mixed signals, and said filtering of the products from said second mixing is performed so that the second product comprises the sum of the mixed signals, the output of the third mixing step is filtered to pass only signals of smaller frequency than twice the sum the unknown and the reference frequency.

4. A method as claimed in claim 2 wherein the filtering of the third mixing step output is performed so as to pass signals of frequency of sufficiently low value that the time varying component of the output signal from the third mixing step is small relative to the non-time varying component.

5. Means for obtaining a signal indicative of an unknown frequency comprising:

means for deriving from a signal of a reference frequency, two signals of said frequency differing from each other in phase by pi /2 radians;

a pair of means designed and connected to mix said unknown frequency, at two separate locations with each of said respective derived frequencies;

means corresponding to each said mixing means for deriving from the output of the corresponding mixer, a signal which is chosen from the class of possible outputs of said mixer which consists of a signal having the frequency of the sum and a signal having the frequency of the difference of the frequencies of the signals mixed; and

where each said means for deriving is designed to derive the same type of signal (i.e., sum or difference of frequencies) from the mixer with which it is connected;

means are provided for delaying one of said derived signals relative to the other;

by the delay Tau , where Tau is chosen from the class of functions consisting of a constant or a function of frequency;

third mixing means are provided for mixing said delayed signal and the other of said derived signals to produce the product thereof.

6. A device as claimed in claim 5 wherein means are provided to ensure that the signals mixed at said third mixing means are of substantially constant amplitude.

7. A device as claimed in claim 5 wherein said delay is a function of the difference of said reference and said unknown frequencies.

8. A device as claimed in claim 6 wherein said delay is a function of the difference of said reference and said unknown frequencies.

9. A device, as claimed in claim 5 wherein said delay is a constant.

10. A device as claimed in claim 6 wherein said delay is a constant.

11. A device as claimed in claim 6 wherein said delay is chosen so that the product of 2 pi times the delay times the difference in frequency over the expected unknown frequency range is not greater than pi and located between adjacent, odd, integral values of + or - pi /2.

12. A device as claimed in claim 7 wherein said deriving means are designed to derive a signal having the frequency of the difference of the signals mixed.

13. A device as claimed in claim 8 wherein said deriving means are designed to derive a signal having the frequency of the difference of the signals mixed.

14. A device as claimed in claim 9 wherein said deriving means are designed to derive a signal having the frequency of the difference of the signals mixed.

15. A device as claimed in claim 10 wherein said deriving means are designed to derive a signal having the frequency of the difference of the signals mixed.

16. A device as claimed in claim 11 wherein said deriving means are designed to derive a signal having the frequency of the difference of the signals mixed.

17. A device as claimed in claim 7 wherein said deriving means are designed to derive a signal having the frequency of the sum of the signals mixed.

18. A device as claimed in claim 8 wherein said deriving means are designed to derive a signal having the frequency of the sum of the signals mixed.

19. A device as claimed in claim 9 wherein said deriving means are designed to derive a signal having the frequency of the sum of the signals mixed.

20. A device as claImed in claim 10 wherein said deriving means are designed to derive a signal having the frequency of the sum of the signals mixed.

21. A device as claimed in claim 11 wherein said deriving means are designed to derive a signal having the frequency of the sum of the signals mixed.

22. A device as claimed in claim 12 combined with means for receiving the output from said third mixing means and for producing therefrom an output from which frequencies higher than a predetermined value have been removed.

23. A device as claimed in claim 13 combined with means for receiving the output from said third mixing means and for producing therefrom an output from which frequencies higher than a predetermined value have been removed.

24. A device as claimed in claim 14 combined with means for receiving the output from said third mixing means and for producing therefrom an output from which frequencies higher than a predetermined value have been removed.

25. A device as claimed in claim 15 combined with means for receiving the output from said third mixing means and for producing therefrom an output from which frequencies higher than a predetermined value have been removed.

26. A device as claimed in claim 16 combined with means for receiving the output from said third mixing means and for producing therefrom an output from which frequencies higher than a predetermined value have been removed.

27. A device as claimed in claim 17 combined with means for receiving the output from said third mixing means and for producing therefrom an output from which frequencies of twice the sum of the unknown and reference frequency, and higher, have been removed.

28. The method as claimed in claim 1 combined with the added step of filtering the output of the third mixer step to substantially remove the time varying component therefrom.