Circuit and method for developing signal indicative of unknown frequency

Claim 3

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.

Claim 4

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.

Claim 5

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.

Claim 6

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.

Claim 7

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.

Claim 8

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.

Claim 9

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

Claim 10

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

Claim 11

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

Claim 12

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

Claim 13

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.

Claim 14

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.

Claim 15

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.

Claim 16

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.

Claim 17

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.

Claim 18

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.

Claim 19

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.

Claim 20

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.

Claim 21

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.

Claim 22

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.

Claim 23

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.

Claim 24

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.

Claim 25

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.

Claim 26

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.

Claim 27

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.

Claim 28

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.

Claim 29

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.

Claim 30

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.