Transponder with reply frequency derived from frequency of received interrogation signal

• US 5,355,513 A
• Filed: 12/28/1990
• Issued: 10/11/1994
• Est. Priority Date: 12/29/1989
• Status: Expired due to Fees

• Current Assignee: Actaris SAS (Itron, Inc.)
• Original Assignee: Schlumberger Industries Incorporated (Schlumberger NV)
• Inventors: Clarke, David J., Martin, Edward A.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Pham, Chi
• Application Number:
  US07/635,066
• Time in Patent Office: 1,383 Days
• Field of Search: 455/15, 455/18, 455/70, 455/75, 455/76, 455/68, 455/69, 455/260, 455/265, 455/119, 455/20, 455/66, 455/, 455/21, 455/23, 455/86, 455/87, 340/825.54, 340/572, 340/870.02, 379/106
• US Class Current: 455/20
• CPC Class Codes: G01S 13/82 wherein continuous-type signals are transmitted
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder

Abstract

A transponder includes a receiver for receiving a radio interrogation signal. The transponder also includes a phase locked loop decoder for deriving a reference signal from the received interrogation signal, and a radio transmitter for transmitting a transponder reply signal. The phase locked loop has an output which feeds the AC reference signal to the transmitter. The transmitter includes a frequency doubler which generates a transmitter radio frequency at double the frequency of the reference signal. The transmitter radio frequency is therefore controlled by the radio frequency of the interrogation signal. The phase locked loop includes a divide-by-N counter, where N is a predetermined integer parameter. The parameter N determines the derivation of the reference signal frequency from the interrogation signal frequency.

Claims

1. Transponder apparatus for transmitting a radio reply signal in response to a radio interrogation signal, comprising:

(a) radio receiver means for receiving said radio interrogation signal, said radio receiver means including;

(i) an antenna for receiving said radio interrogation signal;

(ii) a mixer; and

(iii) an intermediate frequency amplifier coupled to the output of the mixer; and

(b) decoder means for deriving a reference signal from said radio interrogation signal, said decoder means being coupled to the output of the intermediate frequency amplifier and including;

(i) an oscillator;

(ii) phase locked loop means for controlling said oscillator to generate the reference signal at a frequency dependent on the frequency of received radio interrogation signal and offset therefrom by a predetermined offset value; and

(c) radio transmitter means for transmitting a reply signal at a radio frequency derived from said reference signal but different from said radio interrogation frequency, said predetermined offset value being very much smaller than the radio interrogation frequency and the radio reply frequency,

said mixer having inputs comprising said radio interrogation signal from said antenna and the output from said oscillator, whereby said mixer generates an intermediate frequency for application to said intermediate frequency amplifier, said phase locked loop further including a divide-by-N counter coupled to the output of the intermediate frequency amplifier and a phase/frequency detector, said phase/frequency detector having one input connected to the output from said divide-by-N counter and a second input connected to a clock circuit, the parameter N determining said predetermined offset value.

2. Transponder apparatus according to claim 1, wherein the transmitter means includes a frequency multiplier coupled to a transmitter antenna, the reference signal being supplied to the input of the frequency multiplier, and the transmitter radio frequency being an integer multiple of the frequency of the reference signal.

3. Transponder apparatus according to claim 2, wherein the frequency multiplier includes a modulator for encoding a reply message from the transponder into the reply signal.

4. Transponder apparatus according to claim 2, wherein the frequency multiplier is a frequency doubler.

5. Transponder apparatus according to claim 1, wherein the decoder means derives a reference signal of frequency determined by the radio carrier frequency of the interrogation signal.

6. Transponder apparatus according to claim 1, wherein the transponder is switchable between an active state in which the reply signal is transmitted, and a dormant state in which the reply signal is not transmitted, the interrogation signal containing a wake-up signal and a control signal, the transponder including control means for detecting the wake-up signal and subsequently switching the transponder from the dormant to the active state, and for maintaining the transponder in the active state until termination of the control signal whereupon the transponder is returned to the dormant state.

7. Transponder apparatus according to claim 1 further comprising:

(a) means for connecting said apparatus to a commodity supply meter; and

(b) means for encoding the reply signal from said apparatus to include a reply message indicative of the reading of said meter.

8. Transponder apparatus for transmitting a radio reply signal in response to a radio interrogation signal, comprising radio receiver means for receiving the interrogation signal, decoder means for deriving a reference signal from the interrogation signal, the decoder means including an oscillator and means for controlling the oscillator to generate the reference signal at a frequency dependent on the frequency of the received interrogation signal and offset therefrom by a predetermined offset value, and radio transmitter means for transmitting a reply signal at a radio frequency derived from the reference signal, said transponder being switchable between an active state in which the reply signal is transmitted, and a dormant state in which the reply signal is not transmitted, the interrogation signal containing a wake-up signal a control signal, the transponder including control means for detecting the wake-up signal and subsequently switching the transponder from the dormant to the active state, and for maintaining the transponder in the active state until termination of the control signal whereupon the transponder is returned to the dormant state, wherein the wake-up signal is AM modulation of the interrogation signal, and the control signal is FM modulation of the interrogation signal, and wherein the receiver includes an AM demodulator for receiving the wake-up signal, and an FM demodulator for receiving the control signal.

9. Transponder apparatus according to claim 8, wherein the receiver includes a phase locked loop, the transponder being switchable to a semi-active state in which the FM demodulator is enabled with the transmitter means disabled, in use, the control means switching the transponder from the dormant to the semi-active state on reception of the wake-up signal, and subsequently switching the transponder from the semi-active state to the active state when the phase locked loop becomes locked.