Low power regulated amplifier for a transponder

• US 6,982,627 B2
• Filed: 06/13/2003
• Issued: 01/03/2006
• Est. Priority Date: 07/01/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Prexl, Franz, Steinhagen, Wolfgang, Oberhuber, Ralph
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): NGUYEN, NAM V
• Application Number:
  US10/460,824
• Publication Number:
  US 20040135673A1
• Time in Patent Office: 935 Days
• Field of Search: 340/10.1, 340/10.52, 455/245.1, 455/240.1, 455/247.1, 455/248, 455/307, 455/106, 455/107, 455/260, 330/75
• US Class Current: 340/10.1
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• 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: H03G 3/3036 in high-frequency amplifiers or in frequency-changers H03G3/3052, H03G3/32, H03G3/34 take precedence

Abstract

A transponder (1) comprising an antenna (4), a demodulator (5) and a signal processing circuit (6) which converts a modulated signal received via the antenna (4) into a signal suitable for processing in the demodulator (5). The signal processing circuit (6) comprises an amplifier (7) with a predefined amplification factor and a closed loop control circuit (8) serving to maintain the voltage swing of the processed signal applied at the input of the demodulator (5) substantially constant. In a preferred embodiment the closed loop control circuit comprises a capacitor which is continually discharged and differingly charged as a function of the strength of the output signal of the amplifier of the signal processing circuit, the voltage resulting across the capacitor controlling a controllable resistor connected in parallel to the input of the signal processing circuit and forming with a coupling capacitor a voltage divider.

Claims

1. A transponder comprising:

an antenna;

a demodulator;

a signal processing circuit having an output connected to an input of said demodulator and which converts a modulated signal received via said antenna into a processed signal applied at the input of said demodulator and suitable for further processing in said demodulator; and

an amplifier with a predefined amplification factor and a closed loop control circuit serving to maintain the peak-to-peak voltage swing of the processed signal applied at the input of said demodulator substantially constant.

2. The transponder as set forth in claim 1 wherein said closed loop control circuit is configured so that it senses an output signal of said amplifier of said signal processing circuit appearing at the input of said demodulator and controls a controllable resistor, connected in parallel to said input of said signal processing circuit and upstream of the input of said amplifier, as a function of the strength of said output signal.

3. The transponder as set forth in claim 2 wherein said closed loop control circuit comprises a capacitor which is continually discharged and, alternatively, charged as a function of the strength of said output signal of said amplifier of said signal processing circuit, the balance between charging current and discharging current determining the voltage across said capacitor which in turn controls said controllable resistor.

4. The transponder as set forth in claim 3 wherein said closed loop control circuit comprises a first current source for charging said capacitor and a second current source for discharging said capacitor, the current of said first current source being larger than the current of said second current source.

5. The transponder as set forth in claim 4 wherein said closed loop control circuit comprises a further discharging current source, a further charging current source, and one or more switches via which said further current sources can be activated for a certain time period during initialization of said closed loop control circuit to reduce the transient delay of said closed loop control circuit.

6. The transponder as set forth in claim 5 wherein said closed loop control circuit comprises further a clamping diode and a further switch for connecting said clamping diode to said capacitor during initialization of said closed loop control circuit.

7. The transponder as set forth in claim 6 wherein said controllable resistor consists of a MOSFET.

8. The transponder as set forth in claim 1 wherein said demodulator is an ASK demodulator.

9. The transponder as set forth in claim 2 wherein said demodulator is an ASK demodulator.

10. The transponder as set forth in claim 1 wherein the transponder is part of a passive RFID data communication system.

11. The transponder as set forth in claim 2 wherein the transponder is part of a passive REID data communication system.