Telecommunications device using electromagnetic waves

• US 5,173,705 A
• Filed: 11/15/1991
• Issued: 12/22/1992
• Est. Priority Date: 11/16/1990
• Status: Expired due to Fees

• Current Assignee: Thomson Composants Microondes
• Original Assignee: Thomson Composants Microondes
• Inventors: Camiade, Marc, Geffroy, Dominique, Serru, Veronique
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/792,924
• Time in Patent Office: 403 Days
• Field of Search: 342/44, 342/42, 342/51, 342/50
• US Class Current: 342/42
• 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: G07B 15/063 using wireless information transmission between the vehicle and a fixed station identification of vehicles G08G

Abstract

The disclosure relates to the field of data exchange by microwaves between a fixed station, or reader, and a mobile station, or badge. To achieve economy in the energy consumption of the badge, which has a "chip card" format, its input circuit or modem connected to the antenna does not transmit the modulated signal towards the reader. It reflects, in varying degrees, the carrier transmitted by the reader. The modulation of the reflection coefficient of the antenna is obtained by variation of the gate-source junction capacitance, which it itself related to the variation of the gate-source bias voltage of the input transistor of the modem. Application to remote-control toll-gates, remote money transactions and security checks.

Claims

1. A telecommunication device using electromagnetic waves, for exchanging data between a fixed reader station and a mobile badge station,

said fixed reader station comprising:

generating means for generating electromagnetic signals, including an interrogation electromagnetic signal;

a first antenna for transmitting and receiving the electromagnetic signals, including transmitting the interrogation signal;

said mobile badge station comprising;

a second antenna for transmitting electromagnetic signals and receiving electromagnetic signals transmitted from the fixed reader station, including receiving the interrogation signal;

a modulator/demodulator circuit for delivering signals to the second antenna and receiving signals from the second antenna, comprising at least one transistor, with a gate source junction capacitance, which can be in a first state and a second state,

wherein when said transistor is in the first state an impedance of the second antenna is matched to receive electromagnetic signals transmitted from the fixed reader station at the second antenna, and when said transistor is in the second state an impedance of the second antenna is mismatched to reflect signals received at the second antenna back to the first antenna of the fixed reader station; and

an information processing circuit for receiving said interrogation signal from said modulator/demodulator circuit and controlling switching of the transistor from the first state to the second state upon receiving the interrogation signal.

2. The device according to claim 1, wherein the transistor is connected to the second antenna by its gate through a matching network.

3. The device according to claim 2, wherein a variation in the source junction capacitance C_gs of the second antenna is obtained by a variation of a bias voltage V_gs of said transistor.

4. The device according to claim 1, wherein the mobile badge station and fixed reader station communicate by microwaves, in a 1 to 100 GHz band.