Antenna multiplexer with isolation of switching elements
First Claim
1. A transmitter for an electronic article surveillance system, comprising:
- a transmit circuit for generating a transmit signal;
antenna means for receiving the transmit signal generated by the transmit circuit and for radiating the transmit signal into an interrogation zone as an interrogation signal, said antenna means including a first antenna and a second antenna; and
connecting means for transmitting the transmit signal from the transmit circuit to the antenna means, the connecting means including first coupling means for coupling the connecting means to the transmit circuit, second coupling means for coupling the connecting means to the antenna means, and switch means for selectively uncoupling at least one of said first and second antennas from said transmit circuit, the first coupling means having a first impedance and the second coupling means having a second impedance that is matched to said first impedance.
5 Assignments
0 Petitions
Accused Products
Abstract
A multiplexing arrangement for an electronic article surveillance and identification system interconnects a transmitter and a plurality of antennas. The transmitter has first and second terminals and each of the antennas includes an antenna coil. The multiplexing arrangement includes a step down transformer that has a primary winding connected across the first and second terminals of the transmitter, and also has a second winding. A first winding is positioned for inductively coupling with the antenna coil of a first antenna and a second winding is positioned for inductively coupling with the antenna coil of a second antenna. The multiplexing arrangement also includes a first switch and wiring that forms a series loop connection including the first winding, the second winding, the first switch and the secondary winding of the transformer. The first switch is arranged to selectively open-circuit the series loop connection. Also included in the multiplexing arrangement are a second switch connected across the second winding for selectively short-circuiting the second winding and a third switch connected across the first winding for selectively short-circuiting the first winding. The first, second and third switches may be implemented using MOSFETs that are completely isolated from the transmitter.
123 Citations
21 Claims
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1. A transmitter for an electronic article surveillance system, comprising:
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a transmit circuit for generating a transmit signal; antenna means for receiving the transmit signal generated by the transmit circuit and for radiating the transmit signal into an interrogation zone as an interrogation signal, said antenna means including a first antenna and a second antenna; and connecting means for transmitting the transmit signal from the transmit circuit to the antenna means, the connecting means including first coupling means for coupling the connecting means to the transmit circuit, second coupling means for coupling the connecting means to the antenna means, and switch means for selectively uncoupling at least one of said first and second antennas from said transmit circuit, the first coupling means having a first impedance and the second coupling means having a second impedance that is matched to said first impedance. - View Dependent Claims (2, 3, 4, 5)
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6. A transmitter for an electronic article surveillance system, comprising:
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a transmit circuit for generating a transmit signal; antenna means for receiving the transmit signal generated by the transmit circuit and for radiating the transmit signal into an interrogation zone as an interrogation signal; and connecting means for transmitting the transmit signal from the transmit circuit to the antenna means, the connecting means including first coupling means for coupling the connecting means to the transmit circuit, and second coupling means for coupling the connecting means to the antenna means, the first coupling means having a first impedance and the second coupling means having a second impedance that is matched to said first impedance, wherein said first coupling means is a transformer having a primary winding and a secondary winding, said secondary winding having said first impedance.
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7. Apparatus for interconnecting a transmitter and a plurality of antennas, the transmitter having first and second terminals, the plurality of antennas including a first antenna having a first antenna coil, and a second antenna having a second antenna coil, the apparatus comprising:
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a step-down transformer including a primary winding, connected across said first and second terminals of said transmitter, and a secondary winding; a first winding positioned for inductively coupling with said first antenna coil of said first antenna; a second winding positioned for inductively coupling with said second antenna coil of said second antenna; a first switch; means for forming a series loop connection which includes said first winding, said second winding, said first switch, and said secondary winding of said transformer, said first switch arranged to selectively open-circuit said series loop connection; a second switch connected across said second winding for selectively short-circuiting said second winding; and a third switch connected across said first winding for selectively short-circuiting said first winding. - View Dependent Claims (8, 9, 10)
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11. A method of selectively energizing one of a plurality of antennas to radiate a signal generated by a transmitter circuit, each of said plurality of antennas having a respective antenna coil, the method comprising the steps of:
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providing a plurality of windings connected in series, each of said windings corresponding to, and inductively coupled with, a respective one of said antenna coils, said series-connected windings being coupled to said transmitter circuit; and short-circuiting all but one of said windings to select for energizing the antenna coil corresponding to said one of said windings. - View Dependent Claims (12, 13)
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14. Apparatus for interconnecting a transmitter and a plurality of antennas, the transmitter having first and second terminals, the plurality of antennas including a first antenna having a first antenna coil, and a second antenna having a second antenna coil, the apparatus comprising:
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a first winding positioned for inductively coupling with said first antenna coil of said first antenna; a second winding positioned for inductively coupling with said second antenna coil of said second antenna; a first switch; means for forming a series connection of said first winding, said second winding and said first switch; means for coupling said series connection of said first winding, said second winding and said first switch to said transmitter; a second switch connected across said second winding for selectively short-circuiting said second winding; and a third switch connected across said first winding for selectively short-circuiting said first winding. - View Dependent Claims (15, 16, 17)
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18. An antenna multiplexer for supplying a radio frequency signal to a selected one of a plurality of antennas, comprising:
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a plurality of transistor switches, for selecting respective ones of said plurality of antennas and each having a gate terminal; means for filtering said radio frequency signal to form a bias signal; and means for selectively coupling said bias signal to the respective gate terminals of said transistor switches. - View Dependent Claims (19, 20, 21)
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Specification