US 5,206,639 AGranted

Single antenna dual frequency transponder

AssigneeTimex Corporation

InventorBruce Kamens

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Abstract

A single antenna, dual frequency transponder is provided. The transponder includes the antenna, first and second capacitors, a microprocessor/coder for generating a first and second control signals, and a logic circuit which uses the two control signals as inputs and depending on the state of the second control signal either provides an open circuit or a frequency signal at its output node. When the second control signal is a dormant (inhibit) signal, an open circuit is provided. As a result, the capacitors and the antenna provide a first tuned LC circuit which will receive an incoming signal at a desired first frequency. The incoming signal thereby resonates the LC circuit which provides a wake-up signal to the microprocessor/coder. In turn, the microprocessor/coder generates the first control signal of a desired second frequency. In turn, the logic circuit provides a related signal of the same second frequency as an output. With such an output, one of the two capacitors is effectively eliminated from the circuit, and the remaining capacitor and the antenna constitute a second tuned LC circuit which is tuned to the second frequency. By providing adjustable capacitance capacitors, the circuit is adjustable to desired incoming and outgoing frequencies.

A single antenna transponder comprising:

a) signal generating means for generating a first signal of a first desired frequency in response to a trigger signal, and for generating a second control signal having first and second states, said signal generating means changing said second control signal from said first state to said second state after receiving said trigger signal;
b) an antenna coupled to said signal generating means;
c) logic control means coupled to said signal generating means, and including means for receiving said first signal and said second control signal, and having an output, wherein said logic control means includes means for generating a very high impedance at said output when said logic control means receives said first state of said second control signal, and wherein said logic control means includes means for providing a transmitting signal of said first desired frequency when said logic control means receives said first signal and said second state of said second control signal;
d) a first capacitor having a first plate coupled to said output of said logic control means, and a second plate coupled to said antenna and to said signal generating means;
and
e) a second capacitor having a first plate coupled to a first fixed voltage, and a second plate coupled to said first plate of said first capacitor, wherein
when said logic control means receives said first state of said second control signal and said output of said logic control means is at a very high impedance, said first capacitor, said second capacitor, and said antenna comprise a first tuned LC circuit for receiving an incoming signal at a second frequency from which said trigger signal is generated, and
when said logic control means receives said second state of said second control signal, said output of said logic control means is at a low impendance, and said first capacitance and said antenna comprise a second tuned LC circuit for taking said transmitting signal at said first desired frequency and transmitting the same.

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Abstract

Claims18