Radio frequency antenna with current controlled sensitivity

• US 6,574,454 B1
• Filed: 04/04/2000
• Issued: 06/03/2003
• Est. Priority Date: 07/30/1996
• Status: Expired due to Fees

• Current Assignee: Round Rock Research LLC
• Original Assignee: Micron Technology, Inc.
• Inventors: Tuttle, John R.
• Primary Examiner(s): Le, Thanh Cong
• Assistant Examiner(s): Corsaro, Nick
• Application Number:
  US09/542,800
• Time in Patent Office: 1,155 Days
• Field of Search: 455/82, 455/41, 455/121, 455/123, 455/125, 455/254, 455/290, 340/505, 340/572.1, 340/10.1, 343/861, 343/860, 343/850
• US Class Current: 455/41.1
• 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 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 7/005 with variable reactance for tuning the antenna

Abstract

An antenna circuit configured for use in a radio frequency data communications device has an antenna constructed and arranged to transfer electromagnetic waves, the electromagnetic waves corresponding to a signal carried by the antenna and generated from a signal source. A Schottky diode is electrically coupled in serial relation with the antenna, and in operation the signal is applied serially across the antenna and the diode in direct relation with electromagnetic waves transferred by the antenna. A bias current supply is also electrically coupled to the Schottky diode and is configurable to deliver a desired bias current across the current. The diode is responsive to the bias current to realize a desired diode impedance such that a desired impedance match/mis-match is provided between impedance of the diode and impedance of the antenna when the signal is applied across the antenna circuit, which selectively tunes the antenna circuit by imparting a desired power transfer therein. In one version, the antenna receives electromagnetic waves in the form of a radio frequency signal from a separate signal source which imparts a signal carried by the antenna to the antenna circuit such that the antenna circuit is powered by the signal. In another version, a separate signal source is provided in electrical communication with the antenna circuit such that the antenna circuit is powered by the signal source, preferably an oscillating source, which drives the antenna to produce transmitting electromagnetic waves.

Claims

1. A system comprising:

an antenna;

a receiver including a Schottky diode electrically coupled to the antenna; and

a current supply electrically coupled to the Schottky diode and configured to deliver a desired bias current through the Schottky diode wherein reception range of the receiver is adjustable by adjusting the bias current, wherein the antenna has an impedance, wherein the bias current is selected to realize an impedance of the diode that substantially mismatches the impedance of the antenna so as to affect receiver sensitivity.

2. The system of claim 1 wherein the antenna comprises a microstrip antenna.

3. The system of claim 1 and further comprising an integrated circuit defining the receiver.

4. The system of claim 1 wherein the current supply comprises a battery.

5. The system of claim 4 further comprising a potentiometer electrically coupled to the battery and the Schottky diode to provide a voltage divider operable to adjust the current through the Schottky diode.

6. A system in accordance with claim 1 wherein the bias current is selected to realize impedance of the diode to substantially mismatch the impedance of the antenna relative to the diode to affect the reception range to the receiver in direct proportion with the impedance mismatch.

7. A system in accordance with claim 1 wherein the bias current is selected to realize impedance of the diode to substantially mismatch the impedance of the antenna relative to the diode to affect the sensitivity of the receiver in direct proportion with the impedance mismatch.

8. A system comprising:

an antenna;

a receiver including a Schottky diode electrically coupled to the antenna;

a current supply comprising a battery electrically coupled to the Schottky diode and configured to deliver a desired bias current through the Schottky diode wherein reception range of the receiver is adjustable by adjusting the bias current;

a potentiometer electrically coupled to the battery and the Schottky diode to provide a voltage divider operable to adjust the current through the Schottky diode; and

a resistor connected in series between the potentiometer and the Schottky diode, the resistor operable to configure the potentiometer as a substantially ideal current source.

9. The apparatus of claim 8 wherein the Schottky diode is serially coupled to the antenna.

10. The apparatus of claim 8 wherein the antenna has an impedance, and wherein the potentiometer is set so as to select the current through the Schottky diode to realize impedance matching of the Schottky diode relative to the impedance of the impedance.

11. The apparatus of claim 8 wherein the potentiometer is configured to cause the current supply to apply current through the Schottky diode selected to realize a desired impedance.

12. A system in accordance with claim 8 wherein the bias current is selected to realize impedance of the diode to substantially mismatch the impedance of the antenna relative to the diode to affect the reception range to the receiver in direct proportion with the impedance mismatch.

13. A system in accordance with claim 8 wherein the bias current is selected to realize impedance of the diode to substantially mismatch the impedance of the antenna relative to the diode to affect the sensitivity of the receiver in direct proportion with the impedance mismatch.

14. An adjustable radio frequency data communication device comprising:

an antenna having an impedance;

a semiconductor integrated circuit including a transponder, the transponder including a Schottky diode coupled to the antenna;

a signal source configured to apply a signal serially across the antenna and the diode; and

a bias current supply configured to apply a desired bias current through the Schottky diode, the transponder being selectively tunable within a range of detuned and fully tuned states by configuring the bias current through the Schottky diode, the bias current being selected to realize an impedance of the diode that substantially mis-matches the impedance of the antenna so as to affect transponder signal reception sensitivity.

15. The adjustable radio frequency data communication device of claim 14, wherein the Schottky diode is serially connected to the antenna.

16. A system in accordance with claim 14 wherein the bias current is selected to realize impedance of the diode to substantially mismatch the impedance of the antenna relative to the diode to affect the reception range to the receiver in direct proportion with the impedance mismatch.

17. A system in accordance with claim 14 wherein the bias current is selected to realize impedance of the diode to substantially mismatch the impedance of the antenna relative to the diode to affect the sensitivity of the receiver in direct proportion with the impedance mismatch.

18. An adjustable radio frequency data communication device comprising:

an antenna having an impedance;

a semiconductor integrated circuit including a transmitter, the transmitter including a Schottky diode coupled to the antenna;

a transmitter signal source configured to apply a signal serially across the antenna and the diode; and

a bias current supply configured to apply a desired bias current through the Schottky diode, the transmitter sensitivity being adjustable by adjusting the bias current through the Schottky diode to adjust the impedance of the Schottky diode and affect impedance matching of the Schottky diode relative to the antenna, wherein the integrated circuit also includes a receiver, wherein the bias current is selected to realize an impedance of the diode that substantially mis-matches the impedance of the antenna so as to affect receiver signal reception sensitivity.

19. The adjustable radio frequency data communication device of claim 18, wherein the Schottky diode is serially connected to the antenna.

20. An apparatus comprising:

an antenna;

a monolithic semiconductor integrated circuit including a microprocessor and a transponder coupled to the microprocessor, the transponder including a Schottky diode coupled to the antenna; and

an adjustable current supply coupled to the Schottky diode, the transponder being selectively tunable within a range of detuned and fully tuned states by adjusting a bias current through the Schottky diode, wherein the antenna has an impedance, and wherein the bias current is selected to realize an impedance of the diode that substantially mismatches the impedance of the antenna so as to affect transponder signal reception sensitivity.