Switching regulator, transceiver circuit, and keyless access control system

• US 7,728,717 B2
• Filed: 08/20/2007
• Issued: 06/01/2010
• Est. Priority Date: 08/18/2006
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Automotive GmbH (Microchip Technology Incorporated)
• Inventors: Rebholz-Goldmann, Peter
• Primary Examiner(s): Patel; Rajnikant B
• Application Number:
  US11/892,157
• Publication Number:
  US 20080074236A1
• Time in Patent Office: 1,016 Days
• Field of Search: 323282-290, 455/260, 455/333, 455/86, 455/88, 455/552.1, 455/183.2, 307 101- 105, 307/64, 307/66, 340 522- 526, 340 561- 567, 340/426
• US Class Current: 340/286.01
• CPC Class Codes: G07C 9/00944 Details of construction or manufacture
• CPC Class Codes: H04B 1/04 Circuits

Abstract

A switching regulator for controlling transmit antennas of variable impedance, particularly transmit antennas of a keyless access authorization system in or for a vehicle, having an input terminal into which an antenna potential applied or appliable at the transmit antenna may be coupled, and having a control circuit designed to generate a compensation signal as a controlled variable for adapting the antenna potential to an actual output impedance and to establish a slope of the compensation signal depending on the actual antenna potential. The invention relates furthermore to a transceiver circuit with such a switching regulator and to a keyless access control system in or for a vehicle.

Claims

1. A switching regulator for controlling transmit antennas of variable impedance or transmit antennas of a keyless access authorization system in or for a vehicle, the switching regulator comprising:

an input terminal into which an antenna potential applied or appliable at the transmit antenna is coupled; and

a control circuit for generating a compensation signal as a controlled variable for adapting the antenna potential to an actual output impedance and to establish a slope of a compensation signal depending on an actual antenna potential.

2. The switching regulator according to claim 1, further comprising a subtraction circuit that generates a differential signal from an antenna potential and a first supply potential by calculating the difference, and wherein the subtraction circuit has a first differential amplifier.

3. The switching regulator according to claim 2, wherein a voltage ramp generator is provided that generates a ramp-shaped voltage signal from the differential signal, and wherein a slope of the ramp-shaped voltage signal depends on an amplitude of the differential signal.

4. The switching regulator according to claim 3, wherein the voltage ramp generator has a second differential amplifier to generate a constant current from the differential signal and a capacitor which is connected on the output side downstream of the second differential amplifier and is charged and discharged triggered by a clock signal.

5. The switching regulator according to claim 3, wherein the voltage ramp generator has a correction current source that generates a correction current superimposed on the current signal.

6. The switching regulator according to claim 1, further comprising an error amplifier that compares the antenna potential with a reference potential and generates a control signal depending on the comparison.

7. The switching regulator according to claim 1, further comprising a linkage circuit that generates the compensation signal by linking the ramp-shaped voltage signal to the control signal.

8. The switching regulator according to claim 1, further comprising a comparison device that compares the compensation signal with a reference signal derived from an antenna current and on an output side generates a correction signal dependent on the comparison.

9. The switching regulator according to claim 8, wherein a latch, which temporarily stores the correction signal generated by the comparison device, is connected downstream of the comparison device.

10. The switching regulator according to claim 9, wherein the latch is a flip-flop circuit or an RS flip-flop, which is triggered by a clock signal.

11. The switching regulator according to claim 8, wherein at least one controllable switch is connected on the output side downstream of the comparison device, the switch, which is on a control side, is controlled by a control signal provided by or derived from the comparison device and is designed to regulate the output potential in a specified voltage range depending on its control by the control signal.

12. The switching regulator according to claim 1, further comprising:

a first feedback path over which an antenna current flowing through the transmit antenna is fed back to the switching regulator; and

a second feedback path over which the antenna potential applied or appliable at the transmit antenna is fed back to the switching regulator.

13. A transceiver circuit for a device for inductive data transmission or a device for a keyless access control system in or for a vehicle, the transceiver circuit comprising:

at least one antenna resonant circuit for wireless transmission of transmit signals; and

at least one switching regulator to regulate an antenna potential so that the antenna current flowing through the antenna resonant circuit moves back and forth in a zigzag fashion between a preset lower threshold value and a preset upper threshold value, the switching regulator comprising;

an input terminal into which an antenna potential applied or appliable at the transmit antenna is coupled; and

a control circuit for generating a compensation signal as a controlled variable for adapting the antenna potential to an actual output impedance and to establish a slope of a compensation signal depending on an actual antenna potential.

14. The transceiver circuit according to claim 13, wherein at least one driver circuit is provided that is arranged between a first supply terminal with a first supply potential and a second supply terminal with a second supply potential and is connected on an output side to the antenna resonant circuit.

15. The transceiver circuit according to claim 14, wherein the first supply terminal has a positive supply potential and the second supply terminal a reference potential, particularly a ground reference potential.

16. The transceiver circuit according to claim 13, wherein the transmit antenna is a coil antenna with a ferrite core.

17. The transceiver circuit according to claim 13, wherein the transmit antenna has at least one inductive transmit antenna for transmitting transmit signals.

18. The transceiver circuit according to claim 13, wherein the transmit antenna is a series LCR resonant circuit, in which at least one capacitive element, at least one inductive element, and at least one resistive element are arranged in series to one another.

19. The transceiver circuit according to claim 18, wherein the transmit antenna is a parallel LCR resonant circuit, in which at least one capacitive element and at least one inductive element are arranged parallel to one another.

20. A keyless access control system in or for a vehicle, the system comprising:

at least one vehicle-side antenna circuit

at least one vehicle-side transceiver circuit that is connected to the antenna circuit via respective connection lines to control the antenna circuit; and

at least one transponder for communicating via data communication upon approach to the vehicle-side transceiver circuit, the transceiver circuit comprising;

at least one antenna resonant circuit for wireless transmission of transmit signals; and

at least one switching regulator to regulate an antenna potential so that the antenna current flowing through the antenna resonant circuit moves back and forth in a zigzag fashion between a preset lower threshold value and a preset upper threshold value, the switching regulator comprising;

an input terminal into which an antenna potential applied or appliable at the transmit antenna is coupled; and

a control circuit for generating a compensation signal as a controlled variable for adapting the antenna potential to an actual output impedance and to establish a slope of a compensation signal depending on an actual antenna potential.

21. A transceiver circuit for a keyless access control system for a vehicle, the transceiver circuit comprising:

at least one antenna resonant circuit for wireless transmission of transmit signals, the antenna resonant circuit having an antenna configured to receive an antenna potential; and

at least one switching regulator to regulate the antenna potential, the switching regulator comprising;

an input terminal into which the antenna potential is configured to be coupled;

a control circuit for generating a compensation signal as a controlled variable for adapting the antenna potential to an actual output impedance and to establish a slope of a compensation signal depending on an actual antenna potential; and

an output terminal configured to output an output signal based on the compensation signal.

22. The transceiver circuit according to claim 21, wherein the control circuit comprises:

a subtraction circuit that generates a differential signal from the antenna potential and a first supply potential by calculating the difference;

a voltage ramp generator configured to generate a ramp-shaped voltage signal from the differential signal;

a correction current source configured to compare the antenna potential with a reference potential and based on the comparison is configured to generate a control signal; and

a linkage circuit configured to generate the compensation signal by linking the ramp-shaped voltage signal to the control signal.