Radio frequency antenna with current controlled sensitivity

• US 6,122,494 A
• Filed: 10/13/1998
• Issued: 09/19/2000
• Est. Priority Date: 07/30/1996
• Status: Expired due to Term

• Current Assignee: Round Rock Research LLC
• Original Assignee: Micron Technology, Inc.
• Inventors: Tuttle, John R.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Bhattacharya, Sam
• Application Number:
  US09/172,714
• Time in Patent Office: 707 Days
• Field of Search: 455/193.1, 455/38.2, 455/191.1, 455/63, 455/271, 455/66, 455/73, 455/90, 455/191.2, 455/193.3, 455/254, 455/269, 340/825.32, 340/825.54, 342/27, 342/51, 342/42, 343/700 MS, 343/702
• US Class Current: 455/193.1
• 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 in serial relation with the antenna; and

a current supply electrically coupled to the Schottky diode and configured to deliver a desired bias current through the Schottky diode, the Schottky diode being responsive to the bias current to realize a desired impedance across the Schottky diode such that a desired impedance is realized wherein reception range of the receiver is adjustable by adjusting the bias current.

2. The system of claim 1 wherein the bias current is proportioned to realize an impedance of the diode that substantially mis-matches an impedance of the antenna when the antenna is driven by a signal so as to selectively detune the system and realize a desired receiver sensitivity.

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

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

5. The system of claim 1 wherein the current supply comprises a battery electrically connected across the Schottky diode so as to provide a dc bias voltage.

6. The system of claim 5 further comprising a potentiometer electrically coupled to the battery and the Schottky diode to provide a voltage divider operable to adjust the dc bias voltage across the Schottky diode.

7. The system of claim 6 further comprising 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.

8. An apparatus comprising:

a monolithic semiconductor integrated circuit supported by a package and having a microprocessor and a transponder coupled to the microprocessor, the transponder including a Schottky diode serially connected to an antenna; and

an adjustable current supply coupled to the Schottky diode to adjust an impedance of 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.

9. The apparatus of claim 8 wherein the current supply applies a bias current through the Schottky diode selected to realize impedance matching of the Schottky diode relative to an antenna impedance.

10. The apparatus of claim 8 wherein the current supply applies a bias current through the Schottky diode selected to realize a desired impedance.

11. An adjustable radio frequency data communication device comprising:

an antenna;

a semiconductor integrated circuit including a transponder, the transponder including a Schottky diode serially connected 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 to realize a desired impedance of the Schottky diode in relation to impedance of the antenna when receiving the signal, the transponder being selectively tunable within a range of detuned and fully tuned states by configuring the bias current through the Schottky diode to adjust sensitivity of the transponder.

12. An adjustable radio frequency data communication device comprising:

an antenna;

a semiconductor integrated circuit including a transponder, the transponder including a Schottky diode serially connected 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 to realize a desired impedance of the Schottky diode in relation to impedance of the antenna when receiving the signal, the transponder being selectively tunable within a range of tuning states by configuring the bias current through the Schottky diode to adjust sensitivity of the transponder.