Near Field Communications Reader

• US 20130115876A1
• Filed: 11/09/2011
• Published: 05/09/2013
• Est. Priority Date: 11/09/2011
• Status: Active Grant

• Current Assignee: Qualcomm technologies international, ltd. (Qualcomm, Inc.)
• Original Assignee: Cambridge Silicon Radio Limited (Qualcomm, Inc.)
• Inventors: McFARTHING, Anthony
• Granted Patent: US 9,397,385 B2
• Time in Patent Office: Days
• US Class Current: 455/41.1
• CPC Class Codes: G06K 7/10158 methods and means used by the interrogation device for reliably powering the wireless record carriers using an electromagnetic interrogation field
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H03F 2203/45631 the LC comprising one or more capacitors, e.g. coupling capacitors
• CPC Class Codes: H03F 2203/45641 the LC being controlled, e.g. by a signal derived from a non specified place in the dif amp circuit
• CPC Class Codes: H03F 2203/45686 the LC comprising one or more potentiometers, which are not shunting potentiometers
• CPC Class Codes: H03F 2203/45702 the LC comprising two resistors
• CPC Class Codes: H03F 2203/45726 the LC comprising more than one switch, which are not cross coupled
• CPC Class Codes: H03F 3/195 in integrated circuits
• CPC Class Codes: H03F 3/245 with semiconductor devices only
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H04B 5/77 for interrogation

Abstract

The present application relates to a near field communications (NFC) reader having a power amplifier which has an output that connects to an input terminal of an antenna by means of an antenna filter made up of one or more series resistors and one or more series capacitors. The NFC reader includes means for adjusting the Q factor of the antenna so as to increase the available transmit bandwidth and/or improve the efficiency of the reader. The means for adjusting the Q factor of the antenna may be, for example, a variable resistive component or one or more switches.

Claims

1. A near field communications (NFC) reader comprising an amplifier for driving an antenna of the reader and an antenna filter, the reader further comprising means for varying the Q factor of the antenna.

2. A near field communications reader according to claim 1 wherein the means for varying the Q factor of the antenna comprises means for adjusting the output impedance of the amplifier.

3. A near field communications reader according to claim 1 wherein the means for varying the Q factor of the antenna comprises an adjustable resistance connected between an output of the amplifier and the antenna.

4. A near field communications reader according to claim 3 wherein the adjustable resistance is provided by a plurality of selectable resistors.

5. A near field communications reader according to claim 3 wherein the adjustable resistance is provided by a plurality of electrically operable switches, each of which has an on-resistance.

6. A near field communications reader according to claim 3, wherein the adjustable resistance is provided by a digital potentiometer or resistive digital to analogue converter.

7. A near field communications reader according to claim 3, wherein the adjustable resistance is provided by shunt or series feedback around the power amplifier.

8. A near field communications reader according to claim 1 wherein the means for varying the Q factor of the antenna comprises a variable transconductance (g_m) cascode stage in the power amplifier.

9. A near field communications reader according to claim 2 further comprising a controller configured to receive an indication of the data rate of data to be transmitted and to control the means for adjusting the output impedance of the amplifier to accommodate transmission of the data at the indicated data rate.

10. A near field communications reader according to claim 2 wherein the antenna filter comprises a capacitance connected in series between an output of the amplifier and an input of the antenna, the near field communications reader further comprising means for bypassing the capacitance.

11. A near field communications reader comprising an amplifier for driving an antenna of the reader and an antenna filter comprising a capacitance connected in series between an output of the amplifier and an input of the antenna, the near field communications reader further comprising means for bypassing the capacitance.

12. A near field communications reader according to claim 11 wherein the means for bypassing the capacitance comprises a switch connected in parallel with the capacitance such that when activated the switch short circuits the capacitance.

13. A near field communications reader according to claim 11 further comprising a controller for controlling the operation of the switch according to the data rate of data to be transmitted by the near field communications reader.