Method and circuit arrangement for field strength determination and integrated circuit

• US 7,796,965 B2
• Filed: 04/25/2007
• Issued: 09/14/2010
• Est. Priority Date: 04/25/2006
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Automotive GmbH (Microchip Technology Incorporated)
• Inventors: Moser, Daniel, Moser, Helmut
• Primary Examiner(s): Nguyen; Duc M
• Application Number:
  US11/790,492
• Publication Number:
  US 20070257770A1
• Time in Patent Office: 1,238 Days
• Field of Search: 455/41.1, 455/63.1, 455/67.11, 455/226.1, 455/226.2, 455/404.2, 455/456.1, 455/456.6, 340/426.22, 340/426.28, 340/426.36, 340/500, 340/524, 340/539.13, 340/539.21
• US Class Current: 455/226.2
• 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 element of an antenna circuit of an electronic key, wherein the antenna circuit includes at least one circuit element and 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 within said electronic key;

supplying the antenna circuit with the reference input value;

measuring the characteristic parameters, while the antenna circuit is supplied with the reference input value, wherein said characteristic parameters are directly related to values of said antenna element and said at least one circuit element forming said antenna circuit;

storing the characteristic parameters;

measuring a first output value of the antenna circuit; and

determining the field strength as a function of 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. The 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 element and at least one circuit element 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, wherein said characteristic parameters are directly related to values of said antenna element and said at least one circuit element forming said 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 11, wherein the antenna circuit is designed for a mutual coupling to a transmitting antenna of a transmitter of the carrier signal.

16. 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.

17. 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,

wherein the antenna circuit has an antenna coil and a capacitor, which together form a parallel resonant circuit, and

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.

18. A method for determining a distance between a base station and an electronic key based on a field strength of a carrier signal at an antenna of an antenna circuit of the electronic key, wherein the antenna circuit generates an output value that is a function of the field strength and a function of characteristic parameters of the antenna circuit, the method comprising:

determining a second output value as a measure of the characteristic parameters in that a reference input value is generated, the antenna circuit is supplied with the reference input value, the second output value of the antenna circuit is measured while the antenna circuit is supplied with the reference input value, and the second output value is stored; and

measuring a first output value of the antenna circuit, the first output value being produced by a field of the carrier signal while the antenna circuit is not provided with the reference input value;

determining an actual field strength as a quotient of the first output value and the second output value; and

determining the distance based on the actual field strength.