Filtering a single wire protocol (SWP) current signal to be provided to a near field communications (NFC) device

• US 9,031,505 B2
• Filed: 01/13/2014
• Issued: 05/12/2015
• Est. Priority Date: 09/07/2009
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Miles, David John
• Primary Examiner(s): Milord, Marceau
• Application Number:
  US14/153,439
• Publication Number:
  US 20140127998A1
• Time in Patent Office: 484 Days
• Field of Search: 455/41.1, 455/41.2, 455/69, 455/126, 455/80, 455/107, 455/556.2
• US Class Current: 455/41.1
• 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 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10237 the reader and the record carrier being capable of selectively switching between reader and record carrier appearance, e.g. in near field communication [NFC] devices where the NFC device may function as an RFID reader or as an RFID tag
• CPC Class Codes: G06K 7/10247 issues specific to the use of single wire protocol [SWP] in NFC like devices
• CPC Class Codes: H04B 5/00 Near-field transmission systems, e.g. inductive or capacitive transmission systems
• CPC Class Codes: H04B 5/48 Transceivers
• CPC Class Codes: H04L 25/0266 Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
• CPC Class Codes: H04L 25/0282 Provision for current-mode coupling
• CPC Class Codes: H04M 1/72412 using two-way short-range wireless interfaces

Abstract

A communications device is disclosed that includes a united integrated circuit card (UICC) that provides a single wire protocol (SWP) current signal to a near field communications (NFC) device. The SWP current signal is filtered by a filter to remove noise from the SWP current signal. The filter is precharged by a reference voltage when the SWP current signal is in a low state and then filters the SWP current signal when the SWP current signal is in a high state. A switching network provides the filter with the reference voltage to precharge when the SWP is current signal is in the low state and then provides the filter with the SWP current signal to filter when the SWP current signal is in the high state.

Claims

1. An integrated circuit for use in a communications device, the integrated circuit comprising:

a single wire protocol (SWP) interface circuit configured to receive a SWP signal;

a filter configured to filter the SWP signal in a first mode of operation and to be precharged in a second mode of operation;

a first switch configured to provide the SWP signal to the filter in the first mode of operation;

a second switch configured to precharge the filter in the second mode of operation;

a controller configured to transition the communications device from the second mode of operation to the first mode of operation based upon a characteristic of the SWP signal; and

a near field communications (NFC) device configured to receive the filtered SWP signal in the first mode of operation.

2. The integrated circuit of claim 1, further comprising:

a reference voltage module configured to provide a reference voltage to the filter in the second mode of operation.

3. The integrated circuit of claim 2, wherein the filter is configured to be precharged with the reference voltage in the second mode of operation.

4. The integrated circuit of claim 1, further comprising:

a comparator having a first input coupled to the filter and a second input coupled to a reference voltage,

wherein the second switch is further configured to couple the first input to the second input in the second mode of operation to precharge the filter.

5. The integrated circuit of claim 1, wherein the first mode of operation comprises:

the first switch being in a conductive state and the second switch being in a nonconductive state.

6. The integrated circuit of claim 1, wherein the second mode of operation comprises:

the second switch being in a conductive state and the first switch being in a nonconductive state.

7. The integrated circuit of claim 1, wherein the controller is further configured to control when the first switch transitions between a conductive state in the first mode of operation and a nonconductive state in the second mode of operation and when the second circuit switch transitions between the nonconductive state in the first mode of operation and the conductive state in the second mode of operation based on the SWP signal;

wherein the first switch is configured to be transitioned to the conductive state when the second circuit is configured to be transitioned to the nonconductive state; and

wherein the second switch is configured to be transitioned to the conductive state when the first circuit is configured to be transitioned to the nonconductive state.

8. The integrated circuit of claim 7, wherein the controller is further configured to refrain from setting the first switch and the second switch into the conductive state simultaneously and to refrain from setting the first switch and the second switch into the nonconductive state simultaneously.

9. The integrated circuit of claim 1, wherein the controller is further configured to cause the communications device to remain in the second mode of operation for a duration in time, the duration in time being based upon the characteristic of the SWP signal.

10. The integrated circuit of claim 1, wherein the integrated circuit resides in one or more integrated circuit device packages.

11. The integrated circuit of claim 1, wherein the first switch and the second switch are further configured to operate in a complementary manner.

12. A communications device, comprising:

a near field radio frequency (RF) communicator;

an integrated circuit card;

a coupling interface configured to provide a communication between the integrated circuit card and the near field RF communicator using a single wire protocol (SWP), the coupling interface comprising;

a SWP interface circuit configured to receive a SWP current signal and to convert the SWP current signal to a SWP voltage signal;

a filter configured to filter the SWP voltage signal in a first mode of operation and to be precharged in a second mode of operation;

a first switch configured to provide the SWP voltage signal to the filter in the first mode of operation;

a second switch configured to precharge the filter in the second mode of operation;

a controller configured to transition the communications device from the second mode of operation to the first mode of operation based upon a characteristic of the SWP current signal; and

a comparator configured to provide an output signal to the near field RF communicator based upon the filtered SWP voltage signal in the first mode of operation.

13. The communications device of claim 12, further comprising:

a reference voltage module configured to provide a reference voltage to precharge the filter in the second mode of operation.

14. The communications device of claim 12, wherein the controller, is further configured to control when the first switch transitions between a conductive state in the first mode of operation and a nonconductive state in the second mode of operation and when the second switch transitions between the nonconductive state in the first mode of operation and the conductive state in the second mode of operation based on the SWP current signal;

wherein the first switch is configured to be transitioned to the conductive state when the second switch is configured to be transitioned to the nonconductive state; and

wherein the second switch is configured to be transitioned to the conductive state when the first switch is configured to be transitioned to the nonconductive state.

15. The communications device of claim 14, wherein the controller is further configured to cause the communications device to remain in the second mode of operation for a duration in time, the duration in time being based upon the characteristic of the SWP current signal.

16. The communications device of claim 12, wherein the controller is further configured to refrain from setting the first switch and the second switch into a conductive state simultaneously and to refrain from setting the first switch and the second switch into a nonconductive state simultaneously.

17. The communications device of claim 12, wherein the first switch and the second switch are further configured to operate in a complementary manner.

18. A system for filtering a single wire protocol (SWP) current signal, the system comprising:

a SWP interface circuit configured to receive a SWP current signal and to convert the SWP current signal into a SWP voltage signal;

a filter configured to filter the SWP voltage signal in a first mode of operation or to be precharged in a second mode of operation;

a first switch configured to provide the SWP current signal to the filter in the first mode of operation;

a second switch configured to precharge the filter in the second mode of operation;

and

a controller configured to control when the first switch transitions between a conductive state in the first mode of operation and a nonconductive state in the second mode of operation and when the second switch transitions between the nonconductive state in the first mode of operation and the conductive state in the second mode of operation and to cause the communications system to remain in the second mode of operation for a duration in time, the duration in time being based on the SWP current signal.

19. The system according to claim 18, further comprising:

a reference voltage module configured to provide a reference voltage to precharge the filter when the second switch is in the conductive state and the first switch is in the nonconductive state.

20. The system according to claim 18, wherein the first switch and the second switch are further configured to operate in a complementary manner.