Method and circuit arrangement for field strength determination and integrated circuit

• US 20070257770A1
• Filed: 04/25/2007
• Published: 11/08/2007
• Est. Priority Date: 04/25/2006
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Moser, Daniel, Moser, Helmut
• Granted Patent: US 7,796,965 B2
• Time in Patent Office: Days
• US Class Current: 340/5.610
• CPC Class Codes: B60R 2325/105 Radio frequency identification data [RFID]
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: G01R 29/0871 Complete apparatus or systems; circuits, e.g. receivers or amplifiers G01R29/0878, G01R29/0892 take precedence; dosimeters, warning devices G01R29/0857
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 5/26 using coils

Abstract

Method and Circuit Arrangement for Field Strength Determination and Integrated Circuit is provided. In the method of the invention for determining the field strength of a carrier signal at an antenna of an antenna circuit of an electronic key, whereby the antenna circuit generates an output value, which is a function of the field strength and a function of characteristic parameters of the antenna circuit, comprises the steps: generation of a reference input value, supplying the antenna circuit with the reference input value, measurement of the characteristic parameters, while the antenna circuit is supplied with the reference input value, storage of the characteristic parameters, measurement of a first output value of the antenna circuit, and determination of the field strength from the first output value and the characteristic parameters, whereby an effect of the characteristic parameters on the field strength is compensated. Use, for example, in motor vehicles.

Claims

1. A method for determining a field strength of a carrier signal at an antenna of an antenna circuit of an electronic key, wherein the antenna circuit generates an output value, which is a function of the field strength and a function of characteristic parameters of the antenna circuit, the method comprising:

generating a reference input value;

supplying the antenna circuit with the reference input value;

measuring the characteristic parameters, while the antenna circuit is supplied with the reference input value;

storing the characteristic parameters;

measuring a first output value of the antenna circuit; and

determining the field strength from the first output value and the characteristic parameters, wherein an effect of the characteristic parameters on the field strength is compensated.

2. The method according to claim 1, wherein the reference input value is generated in the form of a reference input voltage and/or a reference input current with a predefined reference frequency and reference amplitude, wherein a second output value is measured at an applied reference input value, and wherein the characteristic parameters are determined from the second output value.

3. The method according to claim 2, wherein, to determine the field strength, the quotient is formed from the first output value and the second output value.

4. The method according to claim 2, wherein the reference frequency is set equal to a frequency of the carrier signal.

5. Method according to claim 2, wherein the reference frequency is derived from a frequency of the carrier signal.

6. The method according to claim 1, wherein a distance between the antenna and a transmitting antenna of a transmitter of the carrier signal is determined from the determined field strength.

7. The method according to claim 6, wherein the field strength is determined at a second antenna and at a third antenna, wherein at least one of the antennas are perpendicular to another antenna and a distance between the antennas and a transmitting antenna of a transmitter of the carrier signal is determined from the determined field strengths.

8. The method according to claim 1, wherein the antenna and a transmitting antenna of a transmitter of the carrier signal are coupled mutually.

9. The method according to claim 1, wherein a parallel resonant circuit or a series resonant circuit is formed by the antenna circuit.

10. The method according to claim 1, wherein the frequency of the carrier signal is within a range of 50 KHz to 150 KHz or within a range of 5 MHz to 25 MHz.

11. A circuit arrangement for determining the field strength of a carrier signal, the circuit arrangement comprising:

an antenna circuit with an antenna and an output terminal at which an output value is applied in the form of an output voltage and/or a output current, which is a function of the field strength and a function of characteristic parameters of the antenna circuit;

a reference input value generating unit for generating a reference input value in the form of a reference input voltage and/or a reference input current with a known reference frequency and reference amplitude; and

an activatable switching unit, which is coupled to the antenna circuit and the reference input value generating unit and which supplies the antenna circuit with the reference input value as a function of the activation state or decouples the antenna circuit from the reference input value.

12. The circuit arrangement according to claim 11, wherein the reference input value generating unit is an oscillator.

13. The circuit arrangement according to claim 11, wherein an evaluation unit evaluates an output value when a reference input value is not applied, and evaluates an output value when a reference input value is applied for determining the field strength.

14. The circuit arrangement according to claim 11, wherein the antenna circuit has an antenna coil and a capacitor, which together form a parallel resonant circuit.

15. The circuit arrangement according to claim 14, wherein the switching unit has a first switch, which is looped between a terminal of the capacitor and a reference potential, and a second switch, which is looped between the terminal of the capacitor and a terminal of the reference input value generating unit, at which the reference input value is applied.

16. The circuit arrangement according to claim 11, wherein the antenna circuit is designed for a mutual coupling to a transmitting antenna of a transmitter of the carrier signal.

17. An integrated circuit for a key medium of a passive entry and/or a passive go system, wherein the integrated circuit is designed for coupling to a circuit arrangement according to claim 11.