Apparatus in a communication system

(54) (56) (57)

AGENT

NAME

QUOTES PUBLISHED: SUMMARY:

The present invention relates to a receiver device comprising radio ignition a receiver (104) arranged to receive in two frequency bands (FB₁FB_J). The radio signals within one frequency band (FBj) are communication signals for a radio system (AMPS.NMT) with a certain channel separation, while the radio signals for the other frequency band (FBj)_A) constitute communication signals for another radio system (PCS1900, DCS1800, GSM) with another certain channel separation. The receiver (104) comprises two inputs (108,111) intended for each a radio system with different frequency bands and channel separation. For radio signals appearing on one input (108), down mixing from the radio frequency range is performed directly to the baseband frequency range. On the other hand, for radio signals appearing on the second input (10S), the mixing occurs from the radio frequency range to the baseband frequency range via an intermediate frequency range. Further

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the receiver (104) includes an output (112) intended to deliver baseband signals for both radio systems. The output (112) is connected to a baseband unit common to the radio systems. In the baseband unit, among other things, low pass filtering, detection and neighbor channel suppression are then performed of the received radio signal which has been blended down to the baseband frequency range.

The numbers in brackets indicate international identification code, INlD code. Letters in clamps indicate international document code.

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TECHNICAL FIELD

The present invention relates to a receiver for receiving signals with different frequency bands. The invention is primarily intended to be applied as a receiver in a mobile phone for two different types of networks.

BACKGROUND OF THE ART

Connecting a call between a mobile phone and a mobile phone network when the network is heavily loaded can in many cases fail, because the mobile phone network has a certain upper capacity that limits access to the network. Failed connections occur especially in densely populated areas where, at certain times of the day, call stops occur.

The coverage for mobile phone networks varies geographically. In some areas, coverage may be good for one system, while for another system coverage may be poor.

However, it is in the interest of the mobile phone operator to ensure that as many call connections as possible succeed. For this reason, many mobile phone network operators now wish that one and the same mobile phone can be used for calls in several mobile telephone networks. These mobile telephone networks may be made up of different types of mobile telephone systems, which may mean, for example, that the two systems have different carrier frequencies used in the radio communication between the mobile telephone and the mobile telephone network. These different types of mobile telephone networks can be provided by one and the same mobile telephone network operator. If possible, from for example the mobile phone can always choose the best network, a user can increase their accessibility

508 290 to the mobile phone network and thus more calls will be connected.

Mobile phones usable in several networks for different mobile phone systems basically mean that a transmitter and a receiver are required for each of the mobile phone systems. In order for the mobile phone not to become too large, it is necessary to use the same components for the different systems as much as possible. This means that fewer components are included in the mobile phone, which makes it cheaper, smaller and easier.

European Patent Application EP-678 974 A2 addresses a transmitter and receiver for radio frequency systems. These radio frequency systems are GSM and PCN. The transmitter and receiver are intended to be used for transmission and reception for two different frequency ranges. Common units for the transmitter and receiver are a voltage controlled crystal oscillator that generates a mixer signal L03 with a frequency equal to 26 MHz. Furthermore, two synthesizers are connected to the voltage controlled crystal oscillator. These each generate their mixer signal, LOI and LO2, respectively, using the mixer signal LO3 obtained from the crystal oscillator. The first synthesizer generates the mixer signal L01 at different frequencies depending on the frequency range to be transmitted and received. For GSM, the L01 frequency is equal to 1500 MHz and for PCN the LOI frequency is equal to 1200 MHz. The receiver has a common RF baseband link for both frequency ranges. Thus, the same amplifiers, filters, mixers and I / Q demodulators are used for both frequency ranges. The receiver mixes the mixer signal L01 with the received RF signal and a first intermediate frequency IF1 is obtained.

The first intermediate frequency IF1 obtained is the same for both

508 290 frequency ranges. By varying the mixer signal LOI between the two aforementioned frequencies depending on which frequency range is received, an intermediate frequency IF1 equal to both frequency ranges is obtained. To obtain the least possible spurios, this frequency should be 280.4 MHz for the first intermediate frequency IF1. The first intermediate frequency IF1 is mixed in the next step with the mixer signal LO2 and a second intermediate frequency IF2 is obtained. This intermediate frequency IF2 is demodulated in an I / Q demodulator, whereby an I and Q baseband signal is obtained.

A disadvantage of this solution is that two mixtures of the radio frequency are performed before the I / Q demodulation. This increases power consumption. Keeping power consumption down is of utmost importance in, for example, a mobile phone.

Another disadvantage of this solution is that if two different radio frequency systems are to be received with the receiver, they must have the same channel bandwidth. The receiver thus does not work for radio frequency systems with different channel bandwidth.

European patent application EP-682458A2 deals with a radio communication device intended for transmission and reception in two different digital cellular systems. The device consists of a main unit which enables communication in one digital cellular system (GSM) and an additional unit, which together with the main unit enables communication in the other digital cellular system (PCN). The main unit includes variable filters, two mixers, a variable synthesizer and a power amplifier intended for GSM. The auxiliary unit, which is a power amplifier for PCN, can be connected to the main unit.

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The parameters of the filter and the frequency of the synthesizer output are adjustable. When the auxiliary unit is connected to the main unit, this is detected by a detector connected to a CPU. The CPU commands a controller to set the parameters of the filters and the frequency of the synthesizer output for PCN.

Then the switch is actuated by the control unit so that the power amplifier for the PCN is switched on. When the auxiliary unit is removed, the GSM power amplifier and the filter parameters are connected and the frequency of the synthesizer is again adjusted to GSM.

One disadvantage of this solution is that the add-on unit must be included for the mobile phone to be able to connect to both systems.

Another disadvantage is that upon receiving, a mixture is made into a first intermediate frequency. This mixture causes an unnecessary loss of power for the power supply.

A further disadvantage of this receiver is that this receiver also requires that the two digital cellular systems intended to be received must have the same channel bandwidth.

DISCLOSURE OF THE INVENTION

The present invention addresses a problem in being able to receive radio frequency signals in several different frequency bands in one and the same receiver, where the received signals may have different channel bandwidth in each frequency band.

Another problem encountered by the invention is to be able to use the same baseband portion when receiving radio frequency signals. This means that the number of components in the receiver decreases and which in turn makes the receiver cheap.

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A further problem that the present invention addresses is that radio communication systems with different requirements for mo-agar prerequisite should be able to be received in one and the same receiver.

Thus, it is an object of the present invention to be able to receive various signals

RF range from different radio communication systems with as simplified receiver construction as possible.

The inventive multiband receiver constitutes a link in a receiver chain a

RF signals from various radio communication systems.

The multi-band receiver is in turn arranged with at least two different sub-links, each terminating with an I / Q demodulator.

arranged for a common

The I / Q demodulator outputs are outputs which can then be connected to a common baseband unit.

The signal processing performed on the obtained baseband signals may be different for the different systems, but generally does not pose a problem as this is performed by means of low power and low space-consuming units.

The first sublink in the multiband receiver receives a signal in the RF region with some low channel separation. This signal is amplified, filtered and then mixed at a fixed frequency to obtain a signal in the MF range. The signal in the MF range I / Q is demodulated, whereby an output in a low frequency range is obtained. The low frequency range corresponds to the baseband frequency range of the radio communication system whose RF signal is received.

The second sublink in the multiband receiver receives a signal in the RF range, which signal I / Q demodulates with a higher

508 290 channel separation than the former, whereby an output signal in a different baseband frequency range of the radio communication system whose RF signal is received is obtained. Thus, in the second sub-link, a direct mixing from the RF range to the baseband frequency range is performed, while in the first-mentioned sub-link, the mixture from the RF range to the baseband frequency range is performed via an intermediate frequency range.

An advantage of the present invention is that the same baseband portion can be used for different radio communication systems utilizing different RF ranges.

Another advantage is that the receiver comparatively comprises few components, which means that a simple, inexpensive construction is obtained.

A further advantage of the invention is that since two different methods are used in mixing from the RF range to the baseband frequency range, radio communication systems with different requirements for receiver performance can be received in the multiband receiver according to the invention.

The invention will now be described in more detail with the aid of preferred embodiments and with reference to the accompanying drawing.

DESCRIPTION

Figure 1 shows a schematic view of a transmitter-receiver device.

Figure 2 shows an embodiment of a multiband receiver according to the invention.

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PREFERRED EMBODIMENTS

Figure 1 shows a schematic figure of a transmitter-receiver device in, for example, a mobile telephone for radio communication. The transmitter-receiver device comprises an antenna 100, an antenna combination unit 101, a switch 102 which connects a transmitter 113 and a multiband receiver 104, via a bandpass filter 103, to the antenna combination unit. Further, the transmitter-receiver device includes a duplex filter 106 which connects the transmitter 113 and the multiband receiver 104 to the antenna combination unit 101. The receiver 104 is arranged to receive signals in several different frequency bands for different types of mobile telephone systems in the radio frequency range (RF range). The different types of mobile phone systems can also have different channel separation. For example, the mobile telephone systems may be AMPS in the frequency band 869-894 MHz with the channel separation 30 kHz and PCS in the frequency band 1930-1990 MHz with the channel separation 200 kHz.

Other mobile telephone systems in other frequency bands with different channel separation can, of course, be received when the receiver includes units adapted for these systems. When the receiver chain is adapted for, for example, AMPS and PCS1900, there is the option to receive signals for these two systems. The selection can be done manually or automatically. For example, the system that currently has the best signal-to-noise ratio can be switched on.

Since the frequency bands of received signals in the two systems are different, the antenna 100 must be adapted to the frequency bands of these systems. This is done with the antenna combination unit 101 connected to the antenna 100. The antenna combination unit 101 also functions as a switch. The received RF signal is routed, via switch 102 and bandpass filter 103 or

508 290 the duplex filter 106, to a first input for the RF signal

108 or other input 111 of the inventive multiband receiver 104.

As an example, it is assumed that the device, in Figure 1, is currently configured to be used in the PCS1900 system. The antenna 100 is then adapted by the antenna combination unit 101 for transmitting and receiving in the frequency band around 1900 MHz. The antenna combination unit 101 is connected via the switch 102, which is then in one position in Figure 1, to the first bandpass filter 103 which blocks all frequencies that are outside the range defined for PCS1900. The inventive multiband receiver 104 receives at its input 108 signals which are in the 1900 MHz range defined for PCS1900 and with the channel separation 200 kHz. At the output 112 of the multiband receiver 104, signals are received in a baseband frequency range defined for PCS1900. The frequency content in the baseband frequency range is from zero Hz up to half the channel separation of the radio communication system whose RF signal is received. Thus, since channel separation for PCS1900 is 200 kHz, it means that the frequency content of the signal on the multicast receiver output 112 is 0-100 kHz. The output of the outputs 112 is a signal with two baseband channels in quadrature, that is, two signals with the same information content but with 90 ° phase difference. This concept is well known to one of ordinary skill in the art. In the baseband unit, among other things, low pass filtering, detection and neighbor channel suppression are then performed of the received signal which has been mixed down to the baseband frequency range.

The switch 102 connects in known manner in its second position according to Figure 1 an input 109 of a transmitter 113 to

508 290 antenna combination unit 101. The same antenna 100 is thus used for transmitting and receiving.

When receiving and transmitting for another system, such as AMPS, duplex filter 106 has the same function as switch 102, namely, to separate the transmit and receive signals. In the prior art, the duplex filter 106 is connected to an output 110 of the transmitter 113 and to the input 111 of the receiver 104. At the input 111, the inventive multi-band receiver receives signals in the RF range of AMPS and with a channel separation of 30 kHz. Since the AMPS has the channel separation 30 kHz, the signal obtained at the output 112 includes frequencies in the baseband frequency range 0-15 kHz.

The inventive multiband receiver 104 comprises sAL · at least two inputs 108,111 which receive the signals of the region and at least the output 112 which is connected to the baseband unit 105. The multiband receiver 104 comprises units which allow one and the same output 112 to be able to be. ·. . . and connected to the same input · ρΑ baseband unit 11 ί. This is described in more detail in connection with Figure 2.

The receiver does not necessarily need to be used in conjunction with a transmitter but can constitute a standalone unit in, for example, a paging system that can receive RF signals in two frequency bands.

For example, the multiband receiver 104 can be implemented in an Application Specific Integrated Circuit (ASIC), which makes the multiband receiver 104 small in size. Such implementation of the inventive multiband receiver 104 together with the use of one and the same baseband unit 105,

508 290 means that a smaller receiver with fewer components is obtained. This makes the receiver cheaper to manufacture.

Figure 2 shows an embodiment of the multiband receiver 104 of the present invention.

For a first mobile telephone system (AMPS, NMT) with some low channel separation, whose received signals appear at the input

111 a first mixing of the signal from the radio frequency range to an intermediate frequency range is performed by a mixer 202. Thereafter, an I / Q demodulation of the signal in the intermediate frequency range of an I / Q demodulator 205 is performed, obtaining an output in the baseband frequency range at an output 211.

In a second mobile telephone system (GSM, PCS1900, DCS1800) with somewhat higher channel separation than the first mentioned mobile telephone system, whose signals are received at the input 108, the I / Q demodulation in the I / Q demodulator 213 is performed directly on the received signal in the RF range. An output in the baseband frequency range of the second system's input is obtained at an output 214. The outputs 211,214 are connected to a common output 215 connected to an amplifier 216. Thus, signals obtained at respective outputs 211,214 are amplified in amplifier 216 and the result of the amplified signal is obtained at the output

112 (Figure 1) which includes an output pair 227,228 in Figure 2.

Input 111 is the input of a first amplifier 200 in the multiband receiver 104. Amplifier 200 is an amplifier that amplifies signals in the predominantly radio frequency range. The amplifier 200 can be connected to a bandpass filter 201 which only transmits signals in the current radio frequency range. For example, for AMPS, filter 201 is a bandpass filter with a pass band 869-894 MHz, that is, with a bandwidth 25 MHz.

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The filter 201 is further connected to the mixer 202. The mixer 202 receives the filtered signal obtained from the filter 201 in the RF range and a signal with a previously determined frequency LO ^ from a VCO (Voltage Control Oscillator), whereby a signal in the intermediate frequency range is generated. This intermediate frequency range for AMPS and NMT is about 78 MHz. The corresponding passband for the filter 201 for NMT is 935-960 MHz.

For example, AMPS frequencies LOf are generated_x of said VCO in a frequency range 947-972 MHz and for NMT in the frequency range 1013-1038 MHz.

The mixer 202 is in turn connected to a third bandpass filter 203. This filter 203 filters out all frequencies of the signal in the mid-frequency range which does not include any information for the receiver, for example strong interferers on other channels. For example, for AMPS, filter 203 is constructed with a center frequency of 78 MHz with a bandwidth of ± 15 kHz and for NMT the corresponding center frequency is 78 MHz with the bandwidth ± 12.5 kHz.

The filter 203 is connected to the I / Q demodulator 205. The I / Q demodulator comprises a differential amplifier 204, two mixers 206,207 and a phase shifter 208. Differential amplifier 204 differentiates the signal filtered from filter 203 in the medium frequency range. With the differentiation, signals with better signal / noise are obtained

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characteristics.

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212, which generates

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frequency LOf₂, is connected to the phase shifter 208 and to the mixer 207. As an example, the frequency LOf₂ for

AMPS

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The phase shifter 208, which may, for example, be a passive network, phase shifts the signal generated by oscillator 212, which phase shift signal is mixed with the signal differentiated by differential amplifier 204 and a signal I_A in the baseband frequency range is generated at an output 209 of the I / Q modulator 205. The signal generated by oscillator 212 is mixed with the signal differentiated by differentiator 204, another signal Q_A in the baseband frequency range above output 210 is obtained. The signals I_A and Q_A are two quadrature baseband channels and include frequencies from zero up to half the channel separation of the system whose RF signal has been mixed from the RF range to the baseband frequency range. The I / Q demodulation described above is well known to those skilled in the art.

The outputs 209,210 are connected to each input 226.2: the amplifier 216. The signal I_A is enhanced by at least:. amplifier 223, which for example may be operational amplifier coupled as voltage follower, turns. : output signal I is obtained at an output 228. Similarly, g · amplification of signal Q_A, an output signal Q is obtained at an output 227. The outputs 227 and 228 are referred to as the output 112 of Figure 1.

In the second sub-link for receiving the signals of the second system, the input 108 is an input to an amplifier 224 which amplifies signals with frequencies in the RF range. The amplifier 224 is a component of the second I / Q demodulator 213 which also includes two mixers 220,221 and a phase shifter 222. An oscillator 219 which generates a signal of frequency LOf₃, is connected to the I / Q demodulator 213. For example, for PCS1900, the oscillator 219 generates frequencies in a frequency range 1930

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1990 MHz and for DCS1800 the corresponding frequency range is 18051880.

The I / Q demodulator 213 mixes a received signal at the input 108 by the signal with the frequency LOf₃, in the same manner as the I / Q demodulator 205 described above. Thus, at output 217, a signal I is obtained_d in the baseband frequency range and at an output 218, a signal Q is obtained_d in the baseband frequency range. IN_d and Q_d are two baseband channels in quadrature. The signals I_d, Q_d has a larger baseband frequency range than signals I_A, Q_A. In this case, no down-mixing from RF to MF is required, nor are the additional filters 201,203 included in the first sub-link. For example, for PCS1900, this means a mixture from the RF range 1900 MHz to the baseband frequency range 0-100 kHz.

For example, the amplifiers used in the invention may be operational amplifiers having a predetermined gain or coupled as voltage sensors.

If the multi-band receiver 104 of the invention is implemented as an ASIC, several units, for example, the associated transmitter can be implemented on the ASIC. In this way, even more space is saved, which makes the device for radio frequency even smaller.

The invention is, of course, not limited to only two sub-links but can be realized with more than two sub-links in an inventive manner.

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