Apparatus for compensating non-linearities in frequency-modulated signal
First Claim
1. In a system for interrogating a transponder carrying encoded information, said system comprising:
- (1) means for transmitting a first signal having a time varying first frequency f(t), said first frequency successively assuming a plurality of frequency values within a prescribed frequency range and having, within said range, a monotonically varying average time derivative (df/dt);
(2) remote transponder means for receiving said first signal and for transmitting a second signal in reply thereto, said transponder means including signal transforming means, coupled to receive said first signal as an input, for producing said second signal as an output, said signal transforming means including;
(i) a plurality of signal conditioning means coupled to receive said first signal, each signal conditioning means providing an intermediate signal having a known delay and a known amplitude modification to said first signal; and
(ii) signal combining means coupled to all of said signal conditioning means, for combining said intermediate signals to produce said second signal, said signal conditioning means and said signal combining means imparting a known informational code to said second signal associated with said transponder means;
(3) means for receiving said second signal from said transponder means;
(4) means, coupled to said transmitting means, for producing a third signal derived from said first signal;
(5) means, coupled to said receiving means, for producing a fourth signal derived from said second signal;
(6) first signal mixing means for mixing together said third signal and said fourth signal, thereby to produce a fifth signal;
(7) analog-to-digital converter means, coupled to said first mixing means, for producing digital samples of said fifth signal in response to a sampling signal; and
(8) digital signal processing means, responsive to said digital samples, for analyzing at least some of the frequencies contained in said fifth signal, thereby to determine said informational code associated with said transponder means;
the improvement comprising apparatus for compensating for non-linearities in said average time derivative (df/dt) including;
(a) delay means, coupled to receive as an input signal said first signal, for producing a delayed signal which is a delayed version of said input signal with a prescribed time delay (T1);
(b) second signal mixing means for mixing together said first signal and said delayed signal thereby to produce a sixth signal; and
(c) means responsive to said sixth signal for producing said sampling signal having a frequency which is dependent upon the frequency of said sixth signal, the sampling times of said sampling signal defining those instants at which the first signal has changed in frequency by a prescribed amount Δ
f (Δ
f=1/T1 or a whole fraction or an integer multiple thereof), wherein said analog-to-digital converter means is responsive to said sampling signal for producing a digital sample when said frequency f(t) has changed by said prescribed amount Δ
f.
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Accused Products
Abstract
A "passive interrogator label system" (PILS) comprises an interrogator for transmitting an interrogation signal, one or more "labels" or passive transponders which produce a reply signal containing coded information in response to the interrogation signal, and a receiver and decoder for receiving the reply signal and decoding the information contained in it. The frequency of the interrogation signal assumes a plurality of frequency values within a prescribed frequency range. The decoder includes a mixer (four quadrant multiplier) for mixing together the interrogation and reply signals (or signals derived therefrom) to produce a mixed signal containing frequencies which are the sum and difference of the frequencies of the interrogation and reply signals. A signal processor, responsive to this mixed signal, detects the amplitude and phase of at least some of the frequencies contained in the mixed signal and thereby determines the informational code associated with the transponder. Non-linearity in the transmitted frequency values is compensated by a circuit which produces a sampling signal when the frequency has changed by a prescribed amount Δf. This sampling signal triggers an analog-to-digital converter which converts the mixed signal (or a signal derived therefrom) into a digital value upon receipt of each sampling signal.
43 Citations
14 Claims
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1. In a system for interrogating a transponder carrying encoded information, said system comprising:
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(1) means for transmitting a first signal having a time varying first frequency f(t), said first frequency successively assuming a plurality of frequency values within a prescribed frequency range and having, within said range, a monotonically varying average time derivative (df/dt); (2) remote transponder means for receiving said first signal and for transmitting a second signal in reply thereto, said transponder means including signal transforming means, coupled to receive said first signal as an input, for producing said second signal as an output, said signal transforming means including; (i) a plurality of signal conditioning means coupled to receive said first signal, each signal conditioning means providing an intermediate signal having a known delay and a known amplitude modification to said first signal; and (ii) signal combining means coupled to all of said signal conditioning means, for combining said intermediate signals to produce said second signal, said signal conditioning means and said signal combining means imparting a known informational code to said second signal associated with said transponder means; (3) means for receiving said second signal from said transponder means; (4) means, coupled to said transmitting means, for producing a third signal derived from said first signal; (5) means, coupled to said receiving means, for producing a fourth signal derived from said second signal; (6) first signal mixing means for mixing together said third signal and said fourth signal, thereby to produce a fifth signal; (7) analog-to-digital converter means, coupled to said first mixing means, for producing digital samples of said fifth signal in response to a sampling signal; and (8) digital signal processing means, responsive to said digital samples, for analyzing at least some of the frequencies contained in said fifth signal, thereby to determine said informational code associated with said transponder means; the improvement comprising apparatus for compensating for non-linearities in said average time derivative (df/dt) including; (a) delay means, coupled to receive as an input signal said first signal, for producing a delayed signal which is a delayed version of said input signal with a prescribed time delay (T1); (b) second signal mixing means for mixing together said first signal and said delayed signal thereby to produce a sixth signal; and (c) means responsive to said sixth signal for producing said sampling signal having a frequency which is dependent upon the frequency of said sixth signal, the sampling times of said sampling signal defining those instants at which the first signal has changed in frequency by a prescribed amount Δ
f (Δ
f=1/T1 or a whole fraction or an integer multiple thereof), wherein said analog-to-digital converter means is responsive to said sampling signal for producing a digital sample when said frequency f(t) has changed by said prescribed amount Δ
f. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification