Circuit arrangement and method for phase modulation in a backscattering transponder

• US 7,158,010 B2
• Filed: 05/26/2004
• Issued: 01/02/2007
• Est. Priority Date: 05/28/2003
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Germany GmbH (Microchip Technology Incorporated)
• Inventors: Friedrich, Ulrich, Karthaus, Udo, Fischer, Martin
• Primary Examiner(s): Hofsass; Jeffery
• Assistant Examiner(s): AU, SCOTT D
• Application Number:
  US10/855,865
• Publication Number:
  US 20040257220A1
• Time in Patent Office: 951 Days
• Field of Search: 340/10.41, 340/10.4, 340/10.1, 340/10.2, 340/531
• US Class Current: 340/10.41
• 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: H04B 5/22 Capacitive coupling
• CPC Class Codes: H04B 5/45 Transponders

Abstract

A circuit arrangement for phase modulation in an input circuit of a backscattering transponder includes a varactor and at least one capacitor connected in series between two antenna terminals, and at least two voltage sources selectively connected through at least two switches to at least one terminal of the varactor. A control unit selectively opens and closes the switches in response to the data to be phase-modulated onto the backscattered signal. By selectively connecting the different voltage values of the respective voltage sources to the varactor terminal(s) through the switches, the capacitance of the varactor and correspondingly the input impedance of the input circuit are thereby varied, so as to provide respective different phase positions of the phase modulation.

Claims

1. A circuit arrangement adapted to vary an input impedance of an input circuit of a backscattering transponder to produce a phase modulation of a backscattered signal, said circuit arrangement comprising:

a varactor that has first and second varactor terminals by which said varactor is connected in the input circuit;

first and second voltage sources;

a switching arrangement that is connected between said voltage sources and at least one of said varactor terminals, and that is adapted to selectively conductively connect and disconnect said voltage sources relative to said at least one of said varactor terminals; and

a control unit that has at least one control output connected to at least one control input of said switching arrangement, and that is adapted to control said switching arrangement to selectively conductively connect said voltage sources to said at least one of said varactor terminals depending on a phase position that is to be provided in the phase modulation.

2. The circuit arrangement according to claim 1, wherein said varactor has a capacitance/voltage characteristic that is symmetrical relative to a zero voltage.

3. The circuit arrangement according to claim 1, wherein said switching arrangement comprises at least two high impedance CMOS switching devices.

4. The circuit arrangement according to claim 1, wherein said first voltage source is adapted to provide a ground voltage, and said second voltage source is adapted to provide a supply voltage.

5. The circuit arrangement according to claim 1, wherein said first and second voltage sources are respectively adapted to provide respective voltages of opposite polarity.

6. The circuit arrangement according to claim 1, wherein each one of said voltage sources is respectively a fixed invariable voltage source adapted to provide a respective fixed voltage.

7. The circuit arrangement according to claim 1, excluding any controllable variable voltage source.

8. The circuit arrangement according to claim 1, further comprising a third voltage source selectively connected via said switching arrangement to at least one of said varactor terminals.

9. The circuit arrangement according to claim 1, wherein at least one of said voltage sources is a supply voltage source adapted and connected to provide a supply voltage to the transponder.

10. The circuit arrangement according to claim 1, wherein said control unit further has a data input adapted to receive a data signal that is to be modulated in the phase modulation.

11. The circuit arrangement according to claim 1, further comprising a first capacitor connected in series with said varactor between first and second antenna terminals of the input circuit, and wherein said switching arrangement includes a first switching device that selectively conductively connects said first voltage source to said first varactor terminal and a second switching device that selectively conductively connects said second voltage source to said first varactor terminal.

12. The circuit arrangement according to claim 11, wherein said first capacitor is connected between said first antenna terminal and said first varactor terminal, said second varactor terminal is connected to said second antenna terminal, and the input circuit does not include any further capacitor connected in series with said first capacitor and said varactor between said first and second antenna terminals.

13. The circuit arrangement according to claim 1, further comprising a first capacitor and a second capacitor with said varactor therebetween, connected in series between first and second antenna terminals of the input circuit, and wherein said switching arrangement includes plural switching devices that respectively selectively conductively connect each one of said voltage sources respectively to each one of said varactor terminals.

14. The circuit arrangement according to claim 13, wherein said plural switching devices include a first switching device that selectively conductively connects said first voltage source to said first varactor terminal, a second switching device that selectively conductively connects said second voltage source to said first varactor terminal, a third switching device that selectively conductively connects said first voltage source to said second varactor terminal, and a fourth switching device that selectively conductively connects said second voltage source to said second varactor terminal.

15. A method of producing a phase modulation in a backscattering transponder having a varactor with first and second varactor terminals in an input circuit of said transponder, and having first and second voltage sources, said method comprising the steps:

a) providing control information dependent on a respective phase position of said phase modulation that is to be produced;

b) producing a first voltage with said first voltage source;

c) producing a second voltage with said second voltage source;

d) in response to said control information and dependent on said respective phase position, selectively applying at least one of said first voltage and said second voltage as a control voltage to at least one of said varactor terminals;

e) in response to and dependent on said control voltage, varying a capacitance of said varactor so as to correspondingly vary an input impedance of said input circuit, which produces said phase modulation.

16. The method according to claim 15, wherein said step d) comprises applying said first voltage to said first varactor terminal for a first said phase position and applying said second voltage to said first varactor terminal for a second said phase position different from said first phase position.

17. The method according to claim 15, wherein said step d) comprises applying said first voltage to said first varactor terminal and applying said second voltage to said second varactor terminal for a first said phase position, and applying said second voltage to said first varactor terminal and applying said first voltage to said second varactor terminal for a second said phase position different from said first phase position.

18. The method according to claim 17, wherein said step d) further comprises applying one of said voltages to both said first and second varactor terminals for a third said phase position different from said first and second phase positions.