Radio frequency antenna with current controlled sensitivity

• US 5,970,398 A
• Filed: 08/29/1996
• Issued: 10/19/1999
• Est. Priority Date: 07/30/1996
• Status: Expired due to Term

• Current Assignee: Round Rock Research LLC
• Original Assignee: Micron Communications, Inc. (Micron Technology, Inc.)
• Inventors: Tuttle, John R.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Bhattacharya, Sam
• Application Number:
  US08/704,965
• Time in Patent Office: 1,146 Days
• Field of Search: 455/66, 455/73, 455/90, 455/575, 455/191.1, 455/191.2, 455/193.1, 455/193.2, 455/193.3, 455/195.1, 455/196.1, 455/254, 455/269, 455/271, 455/284, 455/289 , 455/290, 342/42, 342/44, 342/51
• 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 matched/mis-matched 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 radio frequency 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 configurable to deliver a desired bias current across 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 match is provided between impedance of the Schottky diode and impedance of the antenna when the signal is applied across the antenna circuit, 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 wherein the receiver is formed on an integrated circuit.

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 package;

a monolithic semiconductor integrated circuit supported by the package and having a microprocessor and integrated circuitry; and

a transponder coupled to the integrated circuitry of the semiconductor integrated circuit, the transponder including an antenna circuit having an antenna, a Schottky diode serially connected to the antenna, a power supply applied serially across the antenna and the Schottky diode for respectively imparting an impedance across the antenna and the Schottky diode, and an adjustable bias current applied across the Schottky diode to realize a desired impedance of the Schottky diode in relation to impedance of the antenna; and

the transponder being selectively tunable within a range of detuned and fully tuned states by way of configuring the bias current across the Schottky diode which imparts a desired signal sensitivity to the transponder.

9. The apparatus of claim 8 wherein the antenna circuit comprises the antenna, the Schottky diode, and the bias current supply, and the bias current supplied to the Schottky diode is proportioned to realize impedance of the Schottky diode substantially matching impedance of the antenna so as to maximize radio frequency signal sensitivity of the antenna circuit.

10. The apparatus of claim 8 wherein the antenna circuit comprises the antenna, the Schottky diode, and the bias current supply, and the bias current supplied to the Schottky diode is proportioned to realize impedance of the Schottky diode intentionally mis-matched with impedance of the antenna so as to detune the antenna circuit and realize a desired antenna circuit sensitivity.

11. An adjustable radio frequency data communication device comprising:

a semiconductor circuit package including a microprocessor,

a semiconductor integrated circuit supported by the semiconductor circuit package including a discrete semiconductor die having integrated circuitry fabricated therein; and

a transponder electrically connected to the integrated circuitry within the semiconductor circuit package, the transponder including an antenna circuit having an antenna, a Schottky diode serially connected to the antenna, a signal source configured to apply a signal serially across the antenna and the diode for respectively imparting an impedance across the antenna and the diode, a bias current supply configurable to apply a desired bias current across the Schottky diode to realize a desired impedance of the Schottky diode in relation to impedance of the antenna when receiving the signal, the resulting antenna circuit realizing a desired power transfer dependent upon the ratio of antenna impedance to Schottky diode impedance;

the transponder being selectively tunable within a range of detuned and fully tuned states by way of configuring the bias current across the Schottky diode to adjust the sensitivity of the transponder.