GB2365268A

GB2365268A - Antenna switch that reduces interference caused during linearisation by preventing training signals being transmitted or leaked

Info

Publication number: GB2365268A
Application number: GB0018634A
Authority: GB
Inventors: Moshe Ben-Ayun; Mark Rozental; Leonid Kodner
Original assignee: Motorola Israel Ltd
Current assignee: Motorola Solutions Israel Ltd
Priority date: 2000-07-28
Filing date: 2000-07-28
Publication date: 2002-02-13
Anticipated expiration: 2020-07-28
Also published as: GB2365268B; GB0018634D0

Abstract

In a transceiver including a transmission source operably coupled to an antenna along a transmit (TX) path and a receiver operably coupled to the antenna along a receive (RX) path, an antenna switch circuit including a first transformator operably coupled to the TX path at a connection intermediate the antenna and the transmission source along the RX path a second transformator operably coupled to the TX path at a connection intermediate the first transformator and the transmission source and means for controlling the first and second transformators, where the means for controlling is operative to selectably allow a signal transmitted from the transmission source to traverse the TX path and substantially prevent the signal from traversing the RX path, allow a signal received via the antenna to traverse the RX path and substantially prevent the signal from traversing the TX path, and substantially prevent a signal transmitted from the transmission source from traversing at least one of the TX path and the RX path.

Description

<Desc/Clms Page number 1> ANTENNA SWITCH FIELD OF THE INVENTION The present invention relates to radio communications in general, and more particularly to reduced-interference radio transmitter linearization methods and apparatus.

BACKGROUND OF THE INVENTION Digital radio systems that employ multiple radio channels generally require that each transmitter transmit in a substantially linear fashion in order to reduce interference between adjacent channels. In the Terrestrial Trunked Radio (TETRA) system, a logical channel known as the Common Linearization Channel (CLCH) is provided on which transmitter linearization is periodically performed, currently once every four seconds, to ensure proper phase and amplitude of the Cartesian feedback transmitter and to ensure that the transmitter is always ready to transmit.

A prior art antenna switch arrangement may be seen with reference to Fig. 1. While control voltage VCNTO is low, both PIN diodes D1 and D3 are off, the path from the antenna to the receiver (RX) is open, and the radio is in RX mode. While control voltage VCNTO is high, both PIN diodes D1 and D3 are on, the path from the transmitter (TX) to the antenna is open, the path from the antenna to RX is closed, and the radio is in TX mode. During CLCH mode the path from the transmitter (TX) to the antenna is likewise open. Unfortunately, phase and amplitude training signals transmitted via the CLCH tend to interfere with other electronic equipment, as the signals are broadcasted via the transmitter antenna.

SUMMARY OF THE INVENTION The present invention seeks to provide a novel antenna switch configuration that reduces or eliminates interference caused during linearization by preventing training signals from being transmitted via the antenna and attenuating any training signal leakage in the receive path.

There is thus provided in accordance with a preferred embodiment of the present invention, in a transceiver including a transmission source operably coupled to an antenna along a transmit (TX) path and a receiver operably coupled to the antenna along a receive (RX) path, an antenna switch circuit including a first transformator operably coupled to the TX path at a connection intermediate the antenna and the transmission source along the RX path a second transformator operably coupled to the TX path at a connection intermediate the first transformator and the transmission source and means for controlling the first and second transformators, where the means for controlling is operative to selectably allow a signal transmitted from the transmission source to traverse the TX path and substantially prevent the signal from traversing the RX path, allow a signal received via the antenna to traverse the RX path and substantially prevent the signal from traversing the TX path, and substantially prevent a signal transmitted from the transmission source from traversing at least one of the TX path and the RX path.

Further in accordance with a preferred embodiment of the present invention the means for controlling is operative to simultaneously and substantially prevent a signal transmitted from the transmission source from traversing the TX path and the RX path.

Still further in accordance with a preferred embodiment of the present invention the transmission source is an RF power amplifier.

Additionally in accordance with a preferred embodiment of the present invention the TX path includes an isolator coupled to the transmission source and a diode, the diode coupled to a capacitor, the capacitor coupled to the antenna.

Moreover in accordance with a preferred embodiment of the present invention the RX path includes a first capacitor coupled to a second capacitor, the second capacitor coupled to the first transformator, the first transformator coupled to a third capacitor, the third capacitor coupled to the antenna.

Further in accordance with a preferred embodiment of the present invention the means for controlling includes a first control path operably coupled to the RX path, a second control path operably coupled to the second transformator, and a third control path operably coupled to the first transformator.

Still further in accordance with a preferred embodiment of the present invention the first and second control paths are coupled to an XOR gate, the XOR gate providing the origin of the third control path.

Additionally in accordance with a preferred embodiment of the present invention the first control path includes a resistor coupled to a grounded capacitor and a first diode, where the first diode is coupled to a second grounded diode, and where the first and second diodes are operably coupled to the RX path.

Moreover in accordance with a preferred embodiment of the present invention the second control path includes an inverter coupled to a first resistor, the first resistor coupled to a second resistor and to the base of a transistor grounded at an emitter thereat, the second resistor coupled to the collector of the transistor, to a grounded capacitor, and to a diode coupled to the second transformator.

Further in accordance with a preferred embodiment of the present invention the third control path includes an inductor coupled to a resistor and a grounded capacitor, the resistor coupled to the first transformator.

There is also provided in accordance with a preferred embodiment of the present invention, in a transceiver including a transmission source operably

coupled to an antenna along a transmit (TX) path and a receiver operably coupled to the antenna along a receive (RX) path, an antenna switching method including transmitting a signal from the transmission source and controlling a first transformator operably coupled to the TX path at a connection intermediate the antenna and the transmission source along the RX path and a second transformator operably coupled to the TX path at a connection intermediate the first transformator and the transmission source to substantially prevent the signal from traversing at least one of the TX path and the RX path.

Further in accordance with a preferred embodiment of the present invention the transmitting step includes transmitting a CLCH training signal.

Still further in accordance with a preferred embodiment of the present invention the controlling step includes simultaneously and substantially preventing the signal from traversing the TX path and the RX path.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which: Fig. 1 is a diagram of a prior art antenna switch arrangement; and Fig. 2 is a simplified diagram of an antenna switch circuit, constructed and operative in accordance with a preferred embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 2 which is a simplified diagram of an antenna switch circuit, such as for use in a transceiver, constructed and operative in accordance with a preferred embodiment of the present invention. The circuit of Fig. 2 may be controlled by a control line V1 (VCNTO) and a control line V2 (from a controller, not shown) coupled to an XOR gate 10 which feeds a control line V3,

although any suitable controlling arrangement that controls the circuit of Fig. 2 as described hereinbelow may be used. The circuit is preferably operably coupled to a transmission source 12, such as an RF power amplifier, an isolator 14, and an antenna 18. The circuit preferably includes PIN diodes D2, D4, D6, and D8, an inverter 16, quarter wavelength transformators (0/4) 20 and 22, capacitors C2 - C12 which are preferably RF shorts at the RF frequency of operation, resistors R2 - R8, an inductor L2, and a transistor T2. A grounded switch SW1, preferably coupled to a voltage source Vcc, is provided between XOR 10 and inductor L2. V1 (VCNTO) preferably provides sufficient voltage and current to open diodes D6 and D8 as necessary, and Vcc preferably provides sufficient voltage and current to open diodes D2 and D4 as necessary.

Control lines V1, V2, and V3 preferably control the circuit of Fig. 2 in any of three modes as follows:

Antenna Switch (from = Mode controller) Transmit ( T XT1 ( high u (Low) 1 ( high Receive (Rx) a (Low) a Low a (Low) Training (C:LC;h) 1 (High ) high a (Low) In TX mode, V1=1, V2=0, and V3=1. V1=1 causes diodes D6 and D8 to be conductive. 0/4 transformator 22 thus transforms the RF short circuit caused by diodes D6 and D8 to an RF open circuit at antenna 18. V2=0 causes transistor T2 to reach saturation. The RF short circuit at transistor T2 is thus transformed by 0/4 transformator 20 to an RF open circuit at isolator 14 output. V3=1 causes SW1 to close, connecting inductor L2 to voltage source Vcc, which causes diodes D2 and D4 to be conductive and provides collector voltage to transistor T2. The TX path from transmission source 12 to antenna 18 is thus open and the RX path from antenna 18 via 0/4 transformator 22, C4 and C6 is thus closed.

In TX mode the antenna circuit of Fig. 2 behaves similarly to the antenna circuit of Fig. 1 with exception of the o/4 transformator20 - D4 - T2 path. The T2 transistor is in saturation and the D4 diode is conducting, resulting in a RF short at the T2 transistor. Since, from the TX path the RF short is transformed by o/4 transformator 20 into an RF open, there is no additional loss at the TX path during normal TX operation.

In RX mode, V1=0, V2=0, and V3=0. V1=0 causes diodes D6 and D8 to be non-conductive. V2=0 causes the base of transistor T2 to be high, but no voltage is applied to the collector of T2, and, therefore T2 not in saturation. V3=0 causes SW1 to open, connecting inductor L2 to ground, which causes diodes D2 and D4 to be non-conductive. The TX path from transmission source 12 to antenna 18 is thus closed, and the RX path from antenna 18 via I1/4 22, C4 and C6 is thus open. Diodes D6 and D8 also function as limiters during normal RX operation.

In CLCH mode, V1=1, V2=1, and V3=0. V1=1 causes diodes D6 and D8 to be conductive. 0/4 22 thus transforms the RF short circuit caused by D6 and D8 to an RF open circuit at antenna 18. V2=1 causes transistor T2 to not be in saturation. V3=0 causes SW1 to open, connecting inductor L2 to ground, which causes diodes D2 and D4 to be non-conductive. The RF open circuit at the connection between a/4 20 and diode D4 is thus transformed by o/4 20 to RF short circuit at isolator 14 output. This causes a signal that is transmitted from transmission source 12, such as a CLCH training signal, to be greatly attenuated after the isolator 14 output. With diodes D6 and D8 conducting, very little of the signal reaches the receiver. With diode D2 not conducting and an RF short circuit presented to the isolator 14 output, very little of the signal reaches the antenna. Experimentation has shown that the present invention may attenuate CLCH signals by 50-60 dB at antenna 18.

The present invention thus provides an antenna switch circuit that supports RX, TX, and CLCH modes of operation where during CLCH mode the

CLCH signal is not transmitted via the antenna, thus reducing interference to other electronic equipment, and where the CLCH signal does not reach the radio receiver, thus preventing damage to the receiver.

It is appreciated that one or more of the steps of any of the methods described herein may be omitted or carried out in a different order than that shown, without departing from the true spirit and scope of the invention.

While the present invention as disclosed herein may or may not have been described with reference to specific hardware or software, the present invention has been described in a manner sufficient to enable persons of ordinary skill in the art to readily adapt commercially available hardware and software as may be needed to reduce any of the embodiments of the present invention to practice without undue experimentation and using conventional techniques.

While the present invention has been described with reference to one or more specific embodiments, the description is intended to be illustrative of the invention as a whole and is not to be construed as limiting the invention to the embodiments shown. It is appreciated that various modifications may occur to those skilled in the art that, while not specifically shown herein, are nevertheless within the true spirit and scope of the invention.

Claims

CLAIMS What is claimed is: 1. In a transceiver comprising a transmission source operably coupled to an antenna along a transmit (TX) path and a receiver operably coupled to said antenna along a receive (RX) path, an antenna switch circuit comprising: a first transformator operably coupled to said TX path at a connection intermediate said antenna and said transmission source along said RX path; a second transformator operably coupled to said TX path at a connection intermediate said first transformator and said transmission source; and means for controlling said first and second transformators, wherein said means for controlling is operative to selectably: allow a signal transmitted from said transmission source to traverse said TX path and substantially prevent said signal from traversing said RX path, allow a signal received via said antenna to traverse said RX path and substantially prevent said signal from traversing said TX path, and substantially prevent a signal transmitted from said transmission source from traversing at least one of said TX path and said RX path.
2. The antenna switch circuit according to claim 1 wherein said means for controlling is operative to simultaneously and substantially prevent a signal transmitted from said transmission source from traversing said TX path and said RX path.
3. The antenna switch circuit according to claim 1 wherein said transmission source is an RF power amplifier.

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4. The antenna switch circuit according to claim 1 wherein said TX path comprises an isolator coupled to said transmission source and a diode, said diode coupled to a capacitor, said capacitor coupled to said antenna.
5. An antenna switch circuit according to claim 1 wherein said RX path includes a first capacitor coupled to a second capacitor, said second capacitor coupled to said first transformator, said first transformator coupled to a third capacitor, said third capacitor coupled to said antenna.
6. An antenna switch circuit according to claim 1 wherein said signal transmitted from said transmission source is a CLCH training signal.
7. An antenna switch circuit according to claim 1 wherein said means for controlling comprises: a first control path operably coupled to said RX path; a second control path operably coupled to said second transformator; and a third control path operably coupled to said first transformator.
8. An antenna switch circuit according to claim 7 wherein said first and second control paths are coupled to an XOR gate, said XOR gate providing an origin of said third control path.
9. An antenna switch circuit according to claim 7 wherein said first control path comprises a resistor coupled to a grounded capacitor and a first diode, wherein said first diode is coupled to a second grounded diode, and wherein said first and second diodes are operably coupled to said RX path.

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10. An antenna switch circuit according to claim 7 wherein said second control path comprises an inverter coupled to a first resistor, said first resistor coupled to a second resistor and to the base of a transistor grounded at an emitter thereat, said second resistor coupled to the collector of said transistor, to a grounded capacitor, and to a diode coupled to said second transformator.
11. An antenna switch circuit according to claim 7 wherein said third control path includes an inductor coupled to a resistor and a grounded capacitor, said resistor coupled to said first transformator.
12. In a transceiver comprising a transmission source operably coupled to an antenna along a transmit (TX) path and a receiver operably coupled to said antenna along a receive (RX) path, an antenna switching method comprising: transmitting a signal from said transmission source; and controlling a first transformator operably coupled to said TX path at a connection intermediate said antenna and said transmission source along said RX path and a second transformator operably coupled to said TX path at a connection intermediate said first transformator and said transmission source, thereby substantially preventing said signal from traversing at least one of said TX path and said RX path.
13. The method according to claim 12 wherein said transmitting step comprises transmitting a CLCH training signal.
14. The method according to claim 12 wherein said controlling step comprises simultaneously and substantially preventing said signal from traversing said TX path and said RX path.