EMERGENCY CAPACITOR FOR A CONTACTLESS DEVICE

• US 20090127934A1
• Filed: 11/19/2007
• Published: 05/21/2009
• Est. Priority Date: 11/19/2007
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Missoni, Albert, Kargl, Walter, SBUELL, RICHARD
• Granted Patent: US 7,868,481 B2
• Time in Patent Office: Days
• US Class Current: 307/66
• 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 19/07771 the record carrier comprising means for minimising adverse effects on the data communication capability of the record carrier, e.g. minimising Eddy currents induced in a proximate metal or otherwise electromagnetically interfering object
• CPC Class Codes: H02J 50/10 using inductive coupling
• CPC Class Codes: H02J 50/20 using microwaves or radio frequency waves
• CPC Class Codes: H02J 9/061 for DC powered loads

Abstract

A power supply for a contactless device having a power supply circuit configured to provide an internal power supply voltage, an emergency capacitor circuit having an emergency capacitor, configured to provide a source current during an external field pause, and a power supply regulator configured to regulate the internal power supply voltage and the source current, wherein the emergency capacitor circuit is electrically coupled in parallel with the power supply circuit.

Claims

1. A power supply for a contactless device comprising:

a power supply circuit configured to provide an internal power supply voltage;

an emergency capacitor circuit having an emergency capacitor, configured to provide a source current during an external field pause; and

a power supply regulator configured to regulate the internal power supply voltage and the source current,

wherein the emergency capacitor circuit is electrically coupled in parallel with the power supply circuit.

2. The power supply of claim 1, wherein the power supply circuit further comprises a main rectifier circuit configured to rectify an input voltage of the contactless card, wherein the emergency capacitor is electrically coupled to the main rectifier circuit indirectly.

3. The power supply of claim 2, wherein the emergency capacitor circuit further comprises an emergency capacitor rectifier configured to rectify a voltage input to the emergency capacitor.

4. The power supply of claim 1, wherein the power supply circuit comprises a field shunt configured to limit a voltage at an input, and the emergency capacitor is not discharged by the field shunt during an external field pause.

5. The power supply of claim 1, wherein the emergency capacitor circuit further comprises an emergency capacitor rectifier configured to rectify a voltage input to the emergency capacitor.

6. The power supply of claim 1, wherein the emergency capacitor circuit further comprises a switch, which is electrically coupled between the emergency capacitor and the power supply regulator, and is configured to prevent the emergency capacitor from supplying the power supply regulator with the source current when the switch is in an open position.

7. The power supply of claim 6, wherein the power supply circuit further comprises a demodulator, which is configured to detect a beginning of an external field pause and provide a field pause signal to the switch, the field pause signal causing the switch to switch to a closed position and allow the emergency capacitor to supply the power supply regulator with the source current.

8. The power supply of claim 6, wherein the power supply circuit further comprises a demodulator, which is configured to detect an end of an external field pause and to stop providing a field pause signal to the switch, thereby causing the switch to switch to an open position and immediately prevent the emergency capacitor from supplying the power supply regulator with the source current.

9. The power supply of claim 1, wherein the emergency capacitor circuit further comprises a charge limiter configured to limit a charge current of the emergency capacitor as a function of an external field strength available to the contactless card.

10. The power supply of claim 9, wherein the power supply circuit further comprises a field shunt configured to provide the charge limiter with a shunted current signal, which is based on the external field strength available to the contactless card.

11. The power supply of claim 1, wherein the emergency capacitor circuit further comprises a switch configured to prevent the emergency capacitor from discharging.

12. The power supply of claim 1, wherein the emergency capacitor circuit further comprises a current source which is configured to provide the power supply circuit with an amount of current substantially equal to an amount of current consumed by the power supply regulator during a communication mode.

13. The power supply of claim 12, wherein the internal power supply regulator is configured to provide the current source with a current load signal which indicates the amount of current consumed by the power supply regulator during the communication mode.

14. The power supply of claim 1, wherein the contactless device communicates with a reader in accordance with ISO 1443, Type A.

15. The power supply of claim 1, wherein the power supply regulator is electrically coupled in series between the power supply circuit or the energy capacitor circuit and a load.

16. A power supply for a contactless device comprising:

a power supply circuit for providing an internal power supply voltage;

an emergency capacitor circuit, which has an emergency capacitor, for providing a source current during an external field pause; and

a power supply regulator for regulating the internal power supply voltage and the source current,

wherein the emergency capacitor circuit is electrically coupled in parallel with the power supply circuit.

17. A method of charging an emergency capacitor in a contactless card, comprising:

detecting a field strength available to the contactless card; and

limiting charge current of the emergency capacitor as a function of the detected external field strength.

18. The method of claim 17, wherein the detecting step comprises determining an amount of field current shunted at an antenna input of the contactless card, wherein the amount of field current shunted is a function of the external field strength available.

19. A method of discharging an emergency capacitor in a contactless card, comprising:

a current source providing an amount of current consumed by an internal power supply regulator within a regulated power supply circuit; and

limiting current supplied by the current source to the regulated power supply circuit to the amount of consumed current.

20. The method of claim 19, further comprising:

detecting a start of an external field pause; and

closing, in response to the detection, a switch to allow the current source to provide the current to the regulated power supply circuit.

21. The method of claim 19, further comprising:

detecting an end of an external field pause; and

opening, in response to the detecting, a switch to prevent immediately the current source from providing the current to the regulated power supply circuit.