Modulation compensated clamp circuit
First Claim
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1. A transponder of the type used in radio frequency identification systems, comprising:
- a tank circuit;
an overvoltage circuit connected to the tank circuit having a shunting means for shunting current from the tank circuit during an overvoltage condition; and
tuning means for varying the tuning of the tank circuit in accordance with data contained in the transponder, the tuning means operatively coupled with the shunting means to vary the amount of current shunted in accordance with the data.
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Abstract
A radio frequency identification (RFID) tag includes a tank circuit for receiving a power signal transmitted on a radio frequency (RF) carrier by a remote interrogator unit. Information is conveyed from the tag to the interrogator by varying a resistive load placed across the tank circuit as a function of data read from memory. Corresponding variations in the reflected signals are then detected by the interrogator. An overvoltage circuit cooperates with a modulation circuit for providing transmission of data even during an overvoltage condition, thus avoiding masking of the signal under such conditions.
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Citations
18 Claims
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1. A transponder of the type used in radio frequency identification systems, comprising:
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a tank circuit; an overvoltage circuit connected to the tank circuit having a shunting means for shunting current from the tank circuit during an overvoltage condition; and tuning means for varying the tuning of the tank circuit in accordance with data contained in the transponder, the tuning means operatively coupled with the shunting means to vary the amount of current shunted in accordance with the data. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A radio frequency identification transponder comprising:
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first and second terminals; a tank circuit including a coil coupled across the first and second terminals and a capacitor coupled across the first and second terminals; a memory array; a modulation means, coupled to the memory array, for producing a modulation signal which represents data contained in the memory array; a variable resistive load coupled across the first and second terminals, the variable resistive load coupled to the modulation means for providing a variable resistance across the tank circuit in response to the modulation signal; and an overvoltage circuit coupled across the first and second terminals, including a reference voltage circuit coupled to the modulation means to produce a reference voltage that varies in response to the modulation signal, the activation of the overvoltage circuit occurring when a supply voltage exceeds the reference voltage. - View Dependent Claims (8, 9, 10, 11, 12)
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13. In a transponder of a radio frequency identification system, a method of clamping the transponder supply voltage, comprising:
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modulating a resistive load across a tank circuit with a modulation signal; selecting a first voltage reference when the modulation signal is at a first modulation level; selecting a second voltage reference when the modulation signal is at a second modulation level; comparing the supply voltage against a selected reference voltage; and shunting current to across the tank circuit if the supply voltage exceeds the selected reference voltage. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification