AU2009210415B2

AU2009210415B2 - Multi-band telecommunications appparatus

Info

Publication number: AU2009210415B2
Application number: AU2009210415A
Authority: AU
Inventors: Scott Bowman; Isaac Dimanstein; Jared Otto Hoepner; Chase Aiden Johnson; Duane Maxwell Rose; Seppo Saario; Ashely Wade Scandrett
Original assignee: R F Tech Aust Pty Ltd
Current assignee: Rf Technologies Aust Pty Ltd
Priority date: 2008-08-21
Filing date: 2009-08-21
Publication date: 2015-03-26
Anticipated expiration: 2029-08-21
Also published as: AU2009210415A1

Abstract

-18 Multi-band telecommunications apparatus including: an antenna for receiving radio frequency signals in a range of radio frequency bands; a plurality of selectable receiver front ends 5 electrically connected to the antenna for receiving radio frequency signals; a multiplexer for software control of selectable front ends electrically switchable to any one of the front ends; a notch filter for suppression of image frequencies selectively electrically connected to any one of the front ends; 10 a frequency synthesizer circuit for generation of local oscillator frequency; a mixer electrically connected to the notch filter and the frequency synthesizer circuit for reducing high frequency input to an intermediate frequency (IF); a demodulator electrically connected to the mixer for receiving the mixed 15 signals from the notch filter and the frequency synthesizer circuit, the demodulator being operable for suppression of the modulation from the analog signal to retrieve the baseband signal; a baseband decoder unit electrically switchable to the demodulator by a decoder duplexer for software control of the 20 baseband decoder unit; a baseband encoder unit electrically switchable to the frequency synthesizer circuit by an encoder duplexer for software control of the baseband encoder unit; the frequency synthesizer circuit having a modulator electrically connected to the baseband encoder for addition of modulation to 25 the baseband signal; a transmitter front end electrically connected to the frequency synthesizer circuit for amplification and filtering of the modulated signal; a controller operably connected to the multiplexer, the frequency synthesizer circuit including the modulator therein, and the encoder and decoder 30 duplexers for controlling the selectable front ends, configuration of frequency synthesizer circuit, modulation control and selection of the baseband decoder and encoder units. 0( C1) CN 0 C) 0co) I -N N-N 0NFc

Description

-I

MULTI-BAND TELECOMMUNICATIONS APPARATUS FIELD OF INVENTION THIS INVENTION relates to multi-band telecommunications apparatus, generally to voice and data transceivers used in 5 communication devices and in particular to multi band transceivers. The invention is primarily directed to telecommunications over the UHF and VHF bands. However, the invention is not limited to these bands nor to their notional or arbitrary boundaries. 10 BACKGROUNDART Radio frequency spectrum utilisation has long required strict management of frequency allocation. As a result, it is advantageous to provide equipment which operates on a broader range of frequencies. An example of a multi-band transceiver 15 would be one that operates at both very high frequencies (VHF: 140-170 MHz) and ultra high frequencies (UHF: 400-512 MHz). Currently, to achieve multi-band capability with good channel selectivity requires a receive and transmit circuit for each frequency band. This entails additional circuitry such as a 20 crystal filter, a mixer, a low noise amplifier, a matching circuit, voltage controlled oscillator (VCO), a pre-selector as well as the added expense of a dual band antenna. Existing integrated solutions sacrifice channel selectivity to achieve multi-band configuration. In addition integrated 25 solutions do not provide any baseband processing features. Current discrete solutions that combine receive and transmit -2 circuits to provide multi-band capability consist of complex inductor and capacitance tuning circuits. These tuning circuits require configuration or tuning for each particular frequency band where tuning requires physical adjustment. Therefore, they 5 are not truly capable of multi-band operation. The present invention aims to provide multi-band telecommunications apparatus which alleviates one or more of the problems of the prior art. Other aims and advantages of the invention may become apparent from the following description. 10 DISCLOSURE OF THE INVENTION With the foregoing in view, this invention in one aspect resides broadly in multi-band telecommunications apparatus including: an antenna for receiving radio frequency signals in a range 15 of radio frequency bands; a plurality of selectable receiver front ends electrically connected to the antenna for receiving radio frequency signals; a multiplexer for software control of selectable front ends electrically switchable to any one of the front ends; 20 a notch filter for suppression of image frequencies selectively electrically connected to any one of the front ends; a frequency synthesizer circuit for generation of local oscillator frequency; -3 a mixer electrically connected to the notch filter and the frequency synthesizer circuit for reducing high frequency input to an intermediate frequency (IF); a demodulator electrically connected to the mixer for 5 receiving the mixed signals from the notch filter and the frequency synthesizer circuit, the demodulator being operable for suppression of the modulation from the analogue signal to retrieve the baseband signal; a baseband decoder unit electrically switchable to the 10 demodulator by a decoder duplexer for software control of the baseband decoder unit; a baseband encoder unit electrically switchable to the frequency synthesizer circuit by an encoder duplexer for software control of the baseband encoder unit; 15 the frequency synthesizer circuit having a modulator electrically connected to the baseband encoder for addition of modulation to the baseband signal; a transmitter front end electrically connected to the frequency synthesizer circuit for amplification and filtering of 20 the modulated signal; a controller operably connected to the multiplexer, the frequency synthesizer circuit including the modulator therein, and the encoder and decoder duplexers for controlling the selectable front ends, configuration of frequency synthesizer -4 circuit, modulation control and selection of the baseband decoder and encoder units. Preferably, the frequency synthesizer circuit includes a selectable voltage controlled oscillator (VCO) circuit 5 electrically connected to the mixer. Preferably, the frequency synthesizer circuit includes a single multi-band voltage controlled oscillator (VCO) with selectable band mode. Preferably, the frequency synthesizer circuit includes bias compensation for different VCO transistor gain at different 10 bands. Preferably the frequency synthesizer circuit includes a phase lock loop (PLL) for comparison of a reference signal phase to the VCO signal phase to ensure accurate frequency generation. Preferably, the modulator is electrically connected directly into the PLL through a reference signal. 15 In such form, it is preferred that the modulator be electrically connected into the VCO. It is also preferred that the modulator be electrically connected into a mixer. Preferably, the frequency synthesizer circuit includes a filter buffer electrically interposed between the VCO and mixer to provide 20 impedance matching while reducing VCO output harmonics. Preferably, the multi-band telecommunications apparatus includes a zero IF stage. More preferably, the multi-band telecommunications apparatus includes multiple IF stages. The signal may contain voice information and/or data information. 25 In a preferred form, the multi-band telecommunications apparatus has two front ends, one for receiving signals in the -5 ultra high frequency (UHF) band and the other for receiving signals in the very high frequency (VHF) band. The signal may contain voice information on the UHF band. The signal may contain voice information on the VHF band. The signal may contain voice 5 and/or data information on both or either the UHF and VHF bands. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood and put into practical effect, preferred embodiments of the present invention will now be described with reference to the 10 following drawings, and wherein: Fig. 1 is a block diagram of a transceiver according to the invention having dual band capability; and Fig. 2 is a schematic diagram of a single output, dual frequency controlled voltage controlled oscillator with 15 biasing buffer according to the invention. DETAILED DESCRIPTION OF THE DRAWINGS The transceiver 100 shown in Fig 1 comprises a dual band transceiver that may be used in voice and data radio communications. The transceiver circuitry is an example of a 20 multi-band radio frequency transmitter and receiver with two or more frequency modes of operations with baseband decoding and encoding capabilities. The transceiver includes an antenna 102 for receiving a radio frequency (RF) signal 101, where the antenna 102 is electrically connected to a duplexer 103. The 25 duplexer 103 is operable for selecting operating modes, receive or transmit. To receive, the switch is set to connect to a -6 receiving conductor 105 and to transmit the switch is set to connect to a transmitting conductor 145. The selection of the operating mode is communicated by the transmit/receive selection line 104 from a controller in the form of a microprocessor 146. 5 In receive mode the RF signal propagates from the antenna 102 along the receiving conductor 105 to two receiver front ends, a first band front end 106 and a second band front end 107. Each receiver front end enhances the desired band while reducing noise from the unwanted band. For example, when the first band front 10 end 106 is configured for UHF band, a UHF RF signal from the receiving conductor 105 will be matched to a pre-determined impedance whereas a RF signal out of band will be high impedance. In addition, if the receiver front end 107 is configured for VHF band, a VHF RF signal from the receiving conductor 105 will be 15 matched to a pre-determined impedance whereas a RF signal out of band will be high impedance. The input signal from the receiving conductor 105 is enhanced with a Low Noise Amplifier (LNA) (not shown) in each receiver front end. The multiple receiver front ends are electrically connected 20 to a band mode duplexer 111 which is controlled through the band selection control line 110 whose selectivity is under microprocessor control. The band selection control line 110 also configures a dual band VCO 117 for the desired band mode. The band mode duplexer 111 selectively connects which receive front 25 end output signal 108 or 109 is directed to a notch filter 113 along a notch filter input line 112. The result from the notch filter 113 is filtered RF signal free from image frequencies -7 which electrically propagates to a mixer 115. The mixer 115 also accepts a local oscillator (LO) frequency through a filter buffer output line 124 from a filter buffer 123. The generation process of LO frequency through the filter buffer output line 124 is 5 performed by a frequency synthesizer circuit 116 which consists of the dual band VCO 117, a phase-locked loop (PLL) 119, a modulator 141 and a filter buffer 123. The desired frequency is produced by the dual band VCO 117 where the different frequency band range is produced by enabling 10 band specific components of the tuning tank circuit. The VCO output along VCO output line 118 is then directed to the PLL 119. The PLL provides frequency stability and a reduction in phase noise. Any variation in frequency is monitored by the PLL and fed back into the VCO through a VCO-PLL feedback loop 120 for 15 compensation. A stabilised VCO signal is transmitted along a VCO signal line 122 which is electrically connected into the filter buffer 123. The filter buffer 123 provides further harmonic filtering and LO frequency biasing across the different frequency bands to ensure correct mixing operation. The output at the 20 filter buffer output line 125 of the frequency synthesizer is a harmonic filtered biased LO frequency biasing across the different frequency bands to ensure the mixer 115 is sufficiently biased for intermediate frequency (IF) recovery.. The resultant signal out of the mixer 125 is the 25 intermediate frequency (IF) directed along a mixer output line 125, which is supplied to an IF filter 126. The IF filter 126 reduces channel noise by filtering out adjacent channels, thus -8 protecting the desired channel frequency. The analog signal 127 is then ready to be demodulated which is performed by a demodulator 128. The demodulator 128 suppresses the modulated analogue signal 127 to retrieve a baseband signal for 5 transmission out along a demodulator output line 130. For example, the use of Frequency Modulation (FM) would remove the carrier to produce the desired voice or data information. The baseband signal is then routed through a baseband decoder unit 134 or out of the transceiver circuit along a 10 data/audio out line 135. Selectivity of the baseband decoder unit is achieved with a baseband decoder duplexer 131. The baseband decoder duplexer 131 is controlled by the microprocessor control via a baseband processing control line 130. Finally the received signal generates an audio or data signal output along the 15 data/audio out line 135 which is processed by the connected circuitry (not shown) to the transceiver. In transmit mode the audio or data signal is received from external circuitry (not shown) through an input signal line 136. The input signal line 136 is electrically connected to a baseband 20 encoder duplexer 132. The selectivity of baseband encoding by way of a baseband encoder unit 138 is under the microprocessor control 146 which enables or disables through the baseband processing control line 130. The input signal 136 and the baseband decoder unit 138 are connected at a junction 139 which 25 is the baseband signal into the modulator 141. The modulator 141 is under the control of the microprocessor 147 which is responsible for controlling the modulation type and the -9 modulation index, control being achieved through a modulation control line 140. The modulator 141 modulates an analog signal onto the baseband signal at the junction 139 to produce a modulated signal 5 transmitted along a modulated signal line 142. The modulated signal is fed into the PLL 119 as a reference signal input. This produces a variable reference signal that will force the VCO output signal to follow through the VCO-PLL feedback loop 120 which results is a modulated audio/data signal output along a 10 modulated output line 143. The modulated signal couples into the transmit front end 144 for amplification. Matching of the transmit front end 144 to the antenna 103 is achieved by the transmit/receive selection line 104. With the transmit/receive selection line 104 active for transmit the amplified signal is 15 transmitted to the antenna 102 via the transmitting conductor 145. Selection of a particular frequency band is done by a controller, preferably a microprocessor by selecting a receiver front end, configuring the voltage control oscillator (VCO), and 20 phase-lock loop (PLL) . The controller is also responsible for enabling baseband encoder and decoder features. An example of a more detailed frequency synthesizer 116 is illustrated in Fig. 2 in which like reference numerals are carried forward from Fig. 1. The frequency synthesizer 116 25 circuit includes the dual band VCO 117, PLL 119, modulator 141 and filter buffer 123 as described with reference to Fig. 1. The -10 dual band VCO 117 in the current example is based on Colpitts oscillator topology with two switchable parallel resonant tank circuits. The resonant tanks include two varactors 201, 202 in parallel for frequency tuning and two inductors 203, 204 in 5 parallel to one another and each in series with one of the varactors, each inductor being selected for appropriate frequency band. Frequency band selectivity is achieved by connecting one of the tanks via one of two switching diodes 205, 206 while the 10 other tank remains disconnected. The diodes 205, 206 are switched ON by forward bias current that is supplied by field effect transistors (FET's) 207, 208 that are switched ON via a band selection control line 110. The band selection control line is activated and disabled by a controller in the form of a 15 microprocessor 147. The dual band VCO 117 output is electrically connected to the PLL 119 via the VCO output line 118. The PLL 119 is configured by the microprocessor 146. The microprocessor loads the appropriate PLL frequency settings from software 147 which 20 includes the necessary channel settings. The PLL ensures frequency stability by comparing the reference frequency generated by a crystal 213 to the VCO signal output line 118. The difference creates an error signal transmitted through the VCO PLL feedback loop 120 which is feed back into the dual band VCO 25 117 creating a constant feedback compensation.

-11 In transmit mode, the modulator 141 is required to modulate the baseband signal at junction 139. The modulator connects to the crystal 213. The crystal 213 produces a constant reference signal where the modulator 141 induces a variable signal. For 5 example, if the modulation is FM the carrier would be considered the reference signal and information signal considered to be the input signal 142. The result is a difference signal transmitted through the VCO-PLL feedback loop 120, where the difference is the induced variable signal plus the VCO error. This difference 10 signal transmitted through the VCO-PLL feedback loop 120 is fed back into the dual band VCO creating a modulated signal ready for transmission. As the operating frequency bands may differ significantly, the VCO transistors' 207, 208 gains will also vary due to their 15 dependency on frequency. The variation in gain will result in different output power levels from the dual band VCO 117. To compensate for this variation at higher frequency bands additional bias current is supplied to the transistor via a diode 209, this diode is switched ON by the FET 207 when appropriate 20 resonant tank is connected. This extra bias current will increase the gain of the oscillator and as a result the VCO output power will be similar to the level in low frequency band. The VCO output through the signal line 122 contains a fundamental frequency and a number of harmonics. The harmonics 25 are detrimental to signal recovery, therefore need to be reduced to minimize out-of-band interference. Furthermore, a main contributor of phase noise is the overloading of the VCO caused -12 by a mismatch impendence on the VCO output to the connected circuitry. To reduce harmonics and phase noise a buffer filter 123 is employed between the dual band VCO 117 and the mixer 114. The buffer filter 123 matches to a pre-determined impedance of 5 the mixer 114 while presenting a high impedance to the dual band VCO 117 to reduce phase noise. Reduction of harmonics is achieved with a capacitor 211 and a diode 210 configuration as shown in Fig. 2. In the low frequency band, the FET 208 gate current is higher which results in a shift of low pass filters cut-off 10 frequency. The frequency shift is performed by the diode 210 conducting in forward bias mode, which in turn activates the capacitor 211 providing a parallel capacitance with a capacitor 212. The output through the filter buffer output line 124 of the frequency synthesizer is the generation of the local oscillator 15 (LO) with harmonics removed and biased for mixing. It will be seen that the transceiver described provides dual band capability with UHF and VHF frequency bands as examples. The concept of switchable receive, transmit modes, switchable receive front ends, frequency synthesis, demodulation, modulation and 20 baseband decoding/encoding under microprocessor control can be applied to other frequency bands of operation. Furthermore, there is no limitation on the specific number of bands. Accordingly, a multi-band transceiver can now be achieved with superior channel selectivity, low power operation, and is software controllable 25 without the disruption of physical tuning. It is suggested that operation of the transceiver in accordance with the invention would be beneficial to provide -13 multi-band capability with superior channel selectivity without the additional costs associated with creating a multi-band transceiver. The transceiver provides voice and data baseband processing features, low power consumption for portable devices, 5 efficient use of the RF spectrum through superior channel selectivity and selectable modulation types. Operation of band mode, modulation/demodulation type and baseband processing features will be software controlled removing the requirement of physical alteration 10 Although the invention has been described with reference to a specific example, it will be appreciated by those skilled in the art that the invention may be embodied in other forms within the broad scope and ambit of the invention as herein set forth and provisionally defined by the following claims. 15

Claims

1. Multi-band telecommuni nations apparatus including: an antenna to receiving radio frequency signals in a range of radio frequency bands; 5 a plurality of selectable receiver front ends electrically connected to the antenna for receiving radio frequency signals; a multiplexer for software contrci of selectable front ends electrically switchable to any one of the front ends; a notch filter for suppression of image frequencies 10 selectively electrically connected to any one of the front ends; a frequency synthesizer circuit for generation of local oscillator frequency; a mixer electrically connected to the notch filter and the frequency synthesizer circuit for reducing high frequency input 15 to an intermediate frequency (IF); a demodulator electrically connected to the mixer for receiving the mixed signals from the notch filter and the frequency synthesizer circuit, the demodulator being operable for suppression of the modulation from the analog signal to retrieve 20 the baseband signal; a baseband decoder unit electrically switchable to the demodulator by a decoder duplexer for software control of the baseband decoder unit; a baseband encoder unit electrically switchable to the frequency synthesizer circuit by an encoder duplexer for software control of the baseband encoder unit; the frequency synthesizer circuit having a modulator 5 electrically connected to the baseband encoder for addition of modulation to the baseband signal; a transmitter front end electrical connected to the frequency synthesizer circuit for amplification and filtering of the modulated signal; 10 a controller operably connected to the multiplexer, the frequency synthesizer circuit including the modulator therein, and the encoder and decoder duplexers for controlling the selectable front ends, configuration of frequency synthesizer circuit, modulation control and selection of the baseband decoder 15 and encoder units.

2. Multi-band telecommunications apparatus according to Claim 1, wherein the frequency synthesizer circuit includes a selectable voltage controlled oscillator (VCO) circuit electrically connected to the mixer. 20 3. Multi-band telecommunications apparatus according to Claim 1 or Claim 2, wherein the frequency synthesizer circuit includes a single multi-band voltage controlled oscillator (CO) with a selectable band mode.

4. Multi-band telecommunications apparatus according to any one 25 of the preceding claims, wherein the frequency synthesizer -16 circuit includes bias compensation for different VCO transistor gain at different bands.

5. Multi-band telecommunications apparatus according to any one of the preceding claims, wherein the frequency synthesizer 5 circuit includes a phase lock loop (PLL) for comparison of a reference signal phase to the VCO signal phase to ensure accurate frequency generation.

6. Multi-band telecommunications apparatus according to Claim 5, wherein the modulator is electrically connected directly into 10 the PLL through a reference signal.

7. Multi-band telecommunications apparatus according to any one of Claims 3 to 6, wherein modulator is electrically connected into the VCO

8. Multi-band telecommunications apparatus according to any one 15 of Claims 3 to 7, wherein the modulator is electrically connected into a mixer.

9. Multi-band telecommunications apparatus according to any one of Claims 3 to 8, wherein the frequency synthesizer circuit includes a filter buffer electrically interposed between the VCO 20 and mixer to provide impedance matching while reducing VCO output harmonics.

10. Multi-band tel communications apparatus according to any one of the preceding claims, and including a zero IF stage. -17

12. Multi-band telecommunications apparatus according to Claim 10, and including multiple IF stages.

13. Multi-band telecommunications apparatus according to any one of the preceding claims and having two front ends, one for 5 receiving signals in the ultra high frequency (UHF) band and the other for receiving signals in the very high frequency (VHF) band.