GB2344724A

GB2344724A - Transceiver operable in two frequency bands

Info

Publication number: GB2344724A
Application number: GB9927503A
Authority: GB
Inventors: John Howard Waterhouse
Original assignee: Central Research Laboratories Ltd
Current assignee: Central Research Laboratories Ltd
Priority date: 1998-11-19
Filing date: 1999-11-19
Publication date: 2000-06-14
Also published as: GB9927503D0; GB9825412D0; WO2000031886A1

Abstract

The transceiver has a first switch (24b) in the transmission path to switch the transmission signal into one of two frequency bands (TX, (2)) and a second switch (24a) in the receiving path (RX (1)), the transmitting and receiving paths being connected to an antenna. A transmit/receive switch (T/R) connected to the transmission and receiving paths in each band permits switching between transmit and receive modes in each band. The frequency of one of the bands is arranged to be the same as the intermediate frequency of the second band so that a single device is capable of covering a large number of frequency channels.

Description

2344724 A TRANSCEIVER This invention relates to a transceiver and more

particularly, but not exclusively, to a duplex or semi-duplex type transceiver. The transceiver may be operable as an rf 5 transceiver or, when suitably adapted, it may be incorporated in an optoelectronic circuit.

The transceiver will be described with reference to an rf application on an rf board. The rf board is adapted for high data rate communication systems which may be used, for example, in applications such as video and computer links.

In many countries, there are ISM (industrial, scientific and medical) frequencv allocations where no licence is needed, although type approval and power level restrictions must be met. Two of the ISM bands are 2.4 GHz, where 80 N1Hz of spectrum is available and 5.8 GE[z where 150 N4Hz of spectrum is available.

Published European Patent Application EP-A2-780 993 describes a radiotelephone transceiver which is capable of operating over more than one frequency band. The transceiver includes a transmitter and receiver which are connected to a duplexor. Duplexors are expensive and give rise to losses. In addition they are bulky and as mobile telephone handsets become smaller, duplexors occupy a larger proportion of available printed circuit board (PCB) are. Furthermore, significant losses are introduced by band pass filters and mixers at a receiver path stage. These losses can lead to poor sensitivity performance.

The present invention arose to overcome the aforementioned problems and provides an improved transceiver which does not suffer from any of the aforementioned problems.

According to the present invention there is provided a transceiver is operable to receive a signal and to transmit a signal at first and second frequency bands, the transceiver having a first svitch in a transmission path, for switching a signal to be transmitted, at either of 0 "D sid frequency bands; and a receiving path, which in use. is adapted to be connected to an a] n antenna; a second switch connected to said receiving path for switching a received signal.

0 C 2 at either one of said frequency bands, characterised in that a transmit/receive switch is provided to switch selectively between receive and transmit modes for each frequency band.

The received sional and the transmitted sicynal are received and transmitted at the same frequency.

Alternatively signals may be transmitted and received at different frequencies band.

This embodiment may be incorporated into repeater equipment; in which case a power amplifier may be provided for improving the signal-to-noise ratio (SNR); as energy is dissipated when the transceiver operates to transmit and receive in the same frequency band at the same time.

When the transceiver operates in an rf mode the first and second switches may be rf switches. However, when the transceiver operates in an optical device the switches may be a beam splitter or prism or other suitably adapted optoelectronic switch.

Switching is by way of a micro-processor or software control from a personal computer.

Z> Automatic detection means may be provided for detecting signals from one or more I antennae and for determining whether the signals are of sufficient strength. The automatic detection means may include the capability of dynamic channel hopping or switching so as to select a preferred channel and/or antenna.

A diversity switch may be incorporated into an automatic channel hopping function. In addition software may assist the automatic detection of a preferred channel.

The 2.4 GHz band is preferred currently as the 5.8 GHz band generally requires more expensive components and the attainable transmission range is less for a cyiven antenna I In system. However the 5.8 GHz band has more channel capacity and is less prone io interference. The invention permits migration from either band to the other thereb% enhancing flexibility of a svstern.

3 This particular combination reduces the number of components and therefore the cost because certain components can be incorporated into both frequency circuits.

It may be important in some applications that neither systems are compatible with existing systems. A dual band (2.4/5.8 GHz) rf board meets this requirement at a much lower cost and size than, for example, providing 2 separate radios for the bands and clearly offers greater flexibility. This feature of the invention enables dissimilar networks or systems to communicate to one another.

A dual band transceiver has a further benefit in that an operator now has 230 N4Hz of available bandwidth, which can be useful if there are a number of users in the same vicinity. A typical 802.11 standard wireless LAN radio occupies 22 NlHz of spectrum, so it can be seen therefore that each band can only accommodate a small number of users in a given area. These concerns apply to other forms of modulation such as FM, FHSS, and COMM.

An embodiment of the invention will now be described, by way of example only, and with reference to the Figure which shows a circuit diagram of a transceiver.

Referring to the Figure, there is shown a transceiver I having a based band processor 10 for converting a signal to be transmitted into a spread spectrum. Base band filter 12 and up converter converts a base signal, to 280 MHz using a voltage controlled oscillator (VCO).

Surface acoustic wave device (SAW) 14 acts as a bandpass filter. NExer 16 provides an output signal of 2.45 GHz. Synthesizer 18 produces 3.4 GHz output signal for mixing with the 2.45 Ghz signal for subsequent transmission at a first frequency band. Transmission at a second frequency band, typically 2.4 GHz is achieved by switching switch 24b.

4 Baseband and EF (intermediate frequency) sections are shared between both bands.

BFA3624 ic acts as an up/downconvertor from 280 MHz IF frequency to 2.45 GHz which is used for the rf signal when in 2.4 GHz mode. In 5.8 GHz mode these sections are used as a second EF stace. The 2.4/5.8 switching occurs prior to the final mixer sections. Implementation of switch 24 could be by using PRI diodes or an integrated GaASFET switch, both these methods may be software controlled.

The capability of the invention to minimise component cost, especially with regard to channel filtering ensures that legal requirements on imaae rejection and spurious emissions and responses are met.

In 2.4 GHz mode the signal is routed to the power amplifier in transmit mode or the LNA (low noise amplifier) in receive mode. After those stages signals are combined at the transmit/receive switch 24a /24b and pass to (2.4 GHz) filter which is required to reject out-of -band signals from being transmitted or received.

Z> In 5.8 GHz mode the signal from the 2.4/5.8 GHz switch is applied to another mixer stage which converts the signal to 5.8 GHz. The 5.8 GHz signals are routed to a power amplifier and LNA circuits in the same way as for 2.4 GHz. An extra synthesiser is required to generate the 3.4 GHz LO (local oscillator) signal for the 5.8 GH_z mixer stages.

Amplifier 20 increases the rf power level and bandpass filter 21 which acts to provide a si-nal within a narrow licensed bandwidth for transmission to antenna 22.

It is apparent that both transmitter and receiver circuits are incorporated. This operation mode is called half-duplex, the dualband method could also be applied to so called duplex and simplex systems.

The invention may be used in a myriad of applications including. without limitation.

sional aenerator or analysers, telecommunication equipment. mobile telephones. video "D and wLAN based systems.

The invention has been described by way of example only and variations may be made to the embodiment described without departing from the scope of the invention.

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Claims

Claims

I A transceiver is operable to receive a signal and to transmit a siernal at first and second frequency bands, the transciever having a first switch in a transmission path, for switching a signal to be transmitted, at either of said frequency bands.

and a receiving path, which in use, is adapted to be connected to an antenna-, a second switch connected to said receiving path for switching a received signal, at either one of said frequency bands, characterised in that a transmit/receive swtch is provided to switch selectively between receive and transmit modes for each frequency band
2. A transceiver according to claim 1 wherein a transmit/receive switch is provided for each frequency.
3. A transceiver according to either claim I or 2 wherein the first frequency band is substantially the same as the second frequency band.
4. A transceiver accordina to claim 3 wherein the first frequency band is at 2.4 GHz.
5. A transceiver according to claim 3 wherein the first frequency band is at 5.8 GHz.

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6. A transceiver according, to claim I wherein the first frequency band is substantially different from the second frequency band.
7. A transceiver according, to claim 6 wherein the first frequency band is 2.4 GHz and the second frequency band is 5.8 GHz.
8. A transceiver according to any preceding claim where the first switch and/or second switch is a radio frequency (RF) switch.

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9. A transceiver according to any of claims I to 7 wherein the first and/or second switch is an optoelectronic switch.
10. A transceiver accordin- to claim 9 wherein the first and/or second switch is a beam splitter.
11. A transceiver according to claim 9 wherein the first and/or second switch is a Prism.
12. A transceiver according to any preceding claim further including automatic detection means for detecting a signal from at least one antenna and for determining whether the detected signal is of a certain strength.

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