Circuit arrangement with simplified input circuit for phase modulation in a backscattering transponder

• US 20040257293A1
• Filed: 05/26/2004
• Published: 12/23/2004
• 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, Fischer, Martin
• Granted Patent: US 7,173,519 B2
• Time in Patent Office: Days
• US Class Current: 343/860
• CPC Class Codes: G01S 13/756 using a signal generator for modifying the reflectivity of the reflector G01S13/758 takes precedence
• 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

Abstract

A circuit arrangement for phase modulation in an input circuit of a backscattering transponder includes a varactor and at most one capacitor connected in series between two antenna terminals, as well as a varactor control arrangement applying a control voltage to the varactor to selectively vary the capacitance thereof. One of the antenna terminals is connected directly to one of the varactor terminals without a capacitor therebetween. The other antenna terminal is connected either directly or through a capacitor to the other varactor terminal. One antenna terminal and/or one varactor terminal can be grounded. A DC-decoupling capacitor can be connected between a transponder circuit unit or a circuit ground and the common junction of the antenna terminal with the varactor terminal. The circuit arrangement is simple, economical, and uses minimal chip area by omitting further capacitors between the antenna terminals.

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:

first and second antenna terminals in the input circuit adapted to have an antenna connected thereto;

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

a varactor control arrangement connected to at least one of said varactor terminals and adapted to apply a variable control voltage to said varactor so as to vary a capacitance of said varactor; and

zero or at most one capacitor connected in series with said varactor between said first and second antenna terminals.

2. The circuit arrangement according to claim 1, wherein said circuit arrangement does not include any capacitor connected in series with said varactor between said first and second antenna terminals.

3. The circuit arrangement according to claim 2, wherein said first and second antenna terminals are respectively connected directly to said first and second varactor terminals.

4. The circuit arrangement according to claim 1, including said one capacitor connected in series with said varactor between one of said varactor terminals and one of said antenna terminals, and having another of said antenna terminals connected directly to another of said varactor terminals.

5. The circuit arrangement according to claim 1, further in combination with said antenna, which is a closed loop antenna.

6. The circuit arrangement according to claim 1, further in combination with said antenna, which is an open non-loop antenna.

7. The circuit arrangement according to claim 1, wherein one of said antenna terminals is connected to a reference voltage.

8. The circuit arrangement according to claim 7, wherein said reference voltage is a circuit ground of said circuit arrangement.

9. The circuit arrangement according to claim 7, wherein one of said varactor terminals is connected directly to said one of said antenna terminals that is connected to said reference voltage.

10. The circuit arrangement according to claim 7, wherein said one capacitor is connected in series with said varactor between one of said varactor terminals and said one of said antenna terminals that is connected to said reference voltage.

11. The circuit arrangement according to claim 1, further comprising a decoupling capacitor connected between one of said antenna terminals and a reference voltage.

12. The circuit arrangement according to claim 11, wherein said reference voltage is a circuit ground of said circuit arrangement.

13. The circuit arrangement according to claim 11, wherein said one of said antenna terminals is connected directly to one of said varactor terminals.

14. The circuit arrangement according to claim 13, wherein said circuit arrangement does not include any capacitor connected in series with said varactor between said first and second antenna terminals.

15. The circuit arrangement according to claim 1, further comprising a transponder circuit unit connected directly or indirectly to one of said antenna terminals.

16. The circuit arrangement according to claim 15, wherein said transponder circuit unit comprises at least one of a rectifier and a symbol recovery circuit.

17. The circuit arrangement according to claim 15, further comprising a decoupling capacitor connected between said one of said antenna terminals and said transponder circuit unit.

18. The circuit arrangement according to claim 17, wherein said one of said antenna terminals is connected directly to one of said varactor terminals.

19. The circuit arrangement according to claim 15, wherein said transponder circuit unit is connected directly to said one of said antenna terminals.

20. The circuit arrangement according to claim 19, wherein said one capacitor is connected in series with said varactor between one of said varactor terminals and said one of said antenna terminals that is connected directly to said transponder circuit unit.

21. The circuit arrangement according to claim 15, wherein said transponder circuit unit incorporates a decoupling capacitor by which said transponder circuit unit is connected to said one of said antenna terminals.

22. 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:

first and second antenna terminals in the input circuit adapted to have an antenna connected thereto;

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

a varactor control arrangement connected to at least one of said varactor terminals and adapted to apply a variable control voltage to said varactor so as to vary a capacitance of said varactor;

wherein said first antenna terminal is connected directly to said first varactor terminal with no capacitor therebetween.

23. The circuit arrangement according to claim 22, wherein said second antenna terminal is connected directly to said second varactor terminal with no capacitor therebetween.

24. The circuit arrangement according to claim 22, further comprising a capacitor connected in series with said varactor between said second antenna terminal and said second varactor terminal.