Tag responsive to high-frequecy for varying capacitance of tuning capacitor

• US 5,774,062 A
• Filed: 05/25/1995
• Issued: 06/30/1998
• Est. Priority Date: 05/27/1994
• Status: Expired due to Fees

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Ikefuji, Yoshihiro
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): Beaulieu, Yonel
• Application Number:
  US08/450,623
• Time in Patent Office: 1,132 Days
• Field of Search: 340/825.54, 340/825.49, 340/825.35, 340/505, 340/572, 340/539, 340/573, 363/125, 363/126
• US Class Current: 340/10.4
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier

Abstract

A memory stores optimum capacitance values of a variable capacitor obtained by measuring in advance depending on temperatures. In practical use, a controller reads an optimum capacitance value from the memory according to a temperature obtained by a temperature sensor, and sets a capacitance value of the variable capacitor to the optimum capacitance value. Thus, a tuning frequency can be always adjusted to the frequency of a radio wave transmitted. Also, deviation of the tuning frequency due to variations in the production process can be remedied by varying the capacitance value according to data stored in the memory.

Claims

1. A RF-TAG for receiving a high frequency wave from an interrogator to derive electrical power from the high frequency wave and for communicating with the interrogator, the RF-TAG comprising:

a tuning circuit having a tuning coil and a tuning capacitor configured to receive a high frequency wave at a tuning frequency, said tuning capacitor having a variable capacitance value,

a power source circuit connected to an output of the tuning circuit and configured to rectify the output to generate an operating power,

a receiving circuit connected to receive the operating power from the tower source circuit and configured to receive a signal from the tuning circuit,

a transmitting circuit connected to receive the operating power from the power source and configured to supply a transmission signal to the tuning circuit,

a temperature sensor which detects a temperature,

a capacitance value storage memory which stores optimum capacitance values of the tuning capacitor for different temperatures, and

a capacitance value adjusting circuit which adjusts the capacitance values of the tuning capacitor, and is characterized in that;

an optimum capacitance value of the tuning capacitor at the detected temperature is read from the capacitance value storage memory and a capacitance value of the tuning capacitor is set to the optimum capacitance value.

2. A RF-TAG according to claim 1, wherein said tuning capacitor includes a plurality of capacitors and at least one switch, and said capacitance value adjusting circuit controls to turn on/off said switch to vary the capacitance of said tuning capacitor.

3. A RF-TAG according to claim 1, wherein

said capacitance value storage memory is a read-only memory in which a relationship between temperatures and optimum capacitance values is stored in advance.

4. A RF-TAG according to claim 1, wherein said optimum capacitance values comprise values that adjust the tuning frequency to a predetermined value.

5. A system for exchanging prescribed information by receiving a high frequency wave from an interrogator disposed at a prescribed position to derive electrical power from the received signal and using a plurality of RF-TAGs which communicate with said interrogator, wherein each RF-TAG comprises:

a tuning circuit having a tuning coil and a tuning capacitor configured to receive a high frequency wave at a tuning frequency, said tuning capacitor having a variable capacitance value,

a power source circuit connected to an output of the tuning circuit and configured to rectify said output to generate an operating power,

a receiving circuit connected to receive the operating power from the power source circuit and configured to receive a signal from the tuning circuit,

a transmitting circuit connected to receive the operating power from the power source and configured to supply a transmission signal to the tuning circuit,

a temperature sensor which detects a temperature,

a capacitance value storage memory which stores optimum capacitance values of the tuning capacitor for different temperatures, and

a capacitance value adjusting circuit which adjusts the capacitance values of the tuning capacitor, and is characterized in that;

an optimum capacitance value of the tuning capacitor at the detected temperature is read from the capacitance value storage memory and a capacitance value of the tuning capacitor is set to the optimum capacitance value.

6. The system of claim 5, wherein said optimum capacitance values comprise values that adjust the tuning frequency to a predetermined value.

7. A RF-TAG for receiving a high frequency wave from an interrogator to derive electrical power from the high frequency wave and for communicating with the interrogator, comprising:

a tuning circuit having a tuning coil and a tuning capacitor configured to receive a high frequency wave at a tuning frequency, said tuning capacitor having a variable capacitance value;

a power source circuit connected to an output of the tuning circuit and configured to rectify the output to generate an operating power;

a receiving circuit connected to receive the operating power from the power source circuit and configured to receive a signal from the tuning circuit; and

a transmitting circuit connected to receive the operating power from the power source and configured to supply a transmission signal to the tuning circuit;

wherein said variable capacitance of said tuning capacitor is adjustable to adjust the tuning frequency to a predetermined value.

8. A system for exchanging prescribed information by receiving a high frequency wave from an interrogator disposed at a prescribed position to derive electrical power from the received signal and using a plurality of RF-TAGs which communicate with said interrogator, wherein said each RF-TAG comprises:

a tuning circuit having a tuning coil and a tuning capacitor configured to receive a high frequency wave at a tuning frequency, said tuning capacitor having a variable capacitance value;

a power source circuit connected to an output of the tuning circuit and configured to rectify the output to generate an operating power;

a receiving circuit connected to receive the operating power from the power source circuit and configured to receive a signal from the tuning circuit; and

a transmitting circuit connected to receive the operating power from the power source and configured to supply a transmission signal to the tuning circuit;

wherein said variable capacitance of said tuning capacitors of said RF-TAGS are adjustable to adjust the tuning frequency to a predetermined value.