HK1025692B - Apparatus in a communication system - Google Patents

Description

Dual-band receiving device

The present invention relates to a receiver for receiving signals in different frequency bands. The invention is primarily intended for use in a receiver in a mobile telephone operable in two different types of networks.

Establishing a connection between a mobile telephone and a mobile telephone network is often not easy to succeed when the network is heavily loaded, because the mobile telephone network has a certain maximum capacity, which limits the accessibility of the network. Connections are often particularly difficult to succeed during peak hours in densely populated areas.

The coverage of a mobile telephone network varies from geographical area to geographical area. In some areas, one system may have good coverage while the coverage of another network is poor.

The interest of the mobile telephone service operator is to have as many connections as possible to be successfully established. For this reason, many mobile telephone service operators desire that mobile telephones be available within several telephone networks. These mobile telephone networks may comprise different types of mobile telephone systems, for example, which serve radio communication between a mobile telephone set and a mobile telephone network with different carrier frequencies. These different types of mobile telephone networks may be provided by the same mobile telephone service operator. If the best network can be selected, for example by a mobile telephone at any given time, it is easier for the user to access the network and more connections can be set up.

A mobile telephone set which can be used within several different mobile telephone system networks is provided with a transmitter and a receiver for each mobile telephone system. To ensure a reasonable size of the mobile telephone, this means that it is necessary to make the same component available to different systems as much as possible. This reduces the number of parts required in the mobile telephone, which makes the mobile telephone small and light, and also relatively low in cost.

A transmitter and receiver for use in some radio frequency systems is disclosed in european patent application EP 678974 a 2. These radio frequency systems are GSM and PCN. Such transmitters and receivers are used to transmit and receive in two different frequency bands. One of the common components of the transmitter and receiver is a voltage controlled crystal oscillator that generates a mixing signal LO3 at a frequency of 26 MHz. In addition, two frequency synthesizers are connected to the voltage controlled crystal oscillator to generate mixing signals LO1 and LO2, respectively, using mixing signal LO3 received from the crystal oscillator. The first frequency synthesizer generates a mixing signal LO1 having a frequency different according to the frequency band of transmission and reception. For GSM, the frequency of LO1 is 1500MHz, while for PCN, the frequency of LO1 is 1200 MHz. The receiver has an RF baseband link that is common to both frequency bands. Thus, the same amplifier, filter, mixer and I/Q demodulator are used for both frequency bands. The receiver mixes the mixing signal LO1 with the received RF signal to obtain the first intermediate frequency IFI. The first intermediate frequency IFI is the same for both frequency bands. By varying the mixing signal LO1 between the two above-mentioned frequencies depending on the received frequency band, an intermediate frequency IF1 is obtained which is equal for both frequency bands. To minimize interference, the first intermediate frequency IF1 should be taken to be 280.4 MHz. In the next processing step, the first intermediate frequency IF1 is mixed with the mixing signal LO2 to obtain a second intermediate frequency IF 2. This second intermediate frequency IF2 is demodulated in an I/Q demodulator to obtain I and Q baseband signals.

The drawback of this solution is that the radio frequency undergoes two mixing before I/Q demodulation, which increases power consumption. It is of paramount importance to keep the power consumption low, especially for devices like mobile phones.

Another disadvantage of this solution is that the two different radio frequency systems received by the receiver must have the same channel bandwidth. Such receivers cannot operate for radio frequency systems having different channel bandwidths.

European patent application 682458 a2 discloses a radio communication device capable of transmitting and receiving in two different digital cellular systems. The device comprises a primary unit capable of communicating in one of the cellular systems (GSM) and a secondary unit capable of communicating with the primary unit in another digital cellular system (PCN). The main unit comprises variable filters, two mixers, a variable frequency synthesizer and a power amplifier for GSM. The secondary unit is a power amplifier for the PCN and may be connected to the primary unit.

The parameters of the filter and the frequency of the output signal of the frequency synthesizer are adjustable. When the sub unit is connected to the main unit, it is detected by a detector connected to the CPU. The CPU commands a control unit to adjust the parameters of the filter and the frequency of the output signal of the frequency synthesizer to fit them into the PCN. A switch then connects the power amplifier of the PCN under the influence of the control unit. When the sub-unit is switched off, the power amplifier of the GSM is switched on, and the parameters of the filter and the frequency of the frequency synthesizer are readjusted to fit the GSM.

One disadvantage of this solution is that the secondary unit must be configured so that it can connect the mobile telephone to both systems.

Another disadvantage is that mixing is required to obtain the first intermediate frequency when receiving the signal. This mixing implies unnecessary power consumption of the power supply.

This receiver has the further disadvantage that it requires that the two digital cellular systems to be received must have the same channel bandwidth.

The problem to be solved by the invention is to enable one and the same receiver to receive radio frequency signals in several different frequency bands. The received signals may have different channel bandwidths in the respective frequency bands.

Another problem to be solved by the invention is to enable the use of common baseband receiver components in the reception of radio frequency signals. This may reduce the number of components in the receiver, thereby reducing the cost of the receiver.

A problem to be solved by the invention is to enable the same receiver to receive radio signals from radio communication systems having different requirements on receiver performance.

The object of the invention is to make the receiver structure that can receive signals from different radio communication systems in different RF frequency bands as simple as possible.

The multiband receiver according to the invention forms a link within the reception slot for RF signals from different radio communication systems. The multi-band receiver is provided with at least two different sub-links, each terminating in an I/Q demodulator. The outputs of the I/Q demodulators are supplied to a common output which may be connected to a common baseband unit.

The signal processing of the received baseband signal may be different for different systems. This is generally not a problem because the unit performing this processing requires little power and takes up little space.

A first sublink within such a multiband receiver receives signals within an RF zone having a small channel spacing. The received signal is amplified, filtered and mixed with a certain frequency to obtain a signal in the IF region. The IF signal is I/Q demodulated to obtain an output signal in a low frequency region. The low frequency region corresponds to a baseband frequency region of a radio communication system that transmits the received RF signal.

Another sub-link in the multi-band receiver receives signals in the RF region and, after I/Q demodulation with a channel spacing larger than that mentioned above, obtains output signals in a different baseband frequency region, which baseband is used in the radio communication system transmitting the received RF signals. The mixing of the RF band directly into the baseband frequency band is performed in this sub-link, whereas the mixing from the RF band into the baseband frequency band in the first sub-link mentioned above is performed via an intermediate frequency band.

An advantage of the invention is that the same baseband arrangement in such a receiver can be used for different radio communication systems using different RF zones.

Another advantage of the invention is that the receiver uses fewer components, i.e. has a simple structure and is less expensive.

It is still another advantage of the present invention that two different methods are used for mixing from the RF region to the baseband frequency region in the proposed multi-band receiver. This allows access to radio communication systems with different requirements on receiver performance.

The invention will now be described in more detail by means of preferred embodiments with reference to the accompanying drawings. In these drawings:

FIG. 1 is a simplified block diagram of a transceiver device; and

fig. 2 is a schematic diagram of an embodiment of a multi-band receiver constructed in accordance with the present invention.

Fig. 1 is a schematic diagram of a transceiving device in a mobile phone for e.g. radio communication. This transceiver comprises an antenna 100, an antenna combination unit 101 and a switch 102. Switch 102 connects multiband receiver 104 (via bandpass filter 103) and transmitter 113 to antenna combination unit 101. The transceiver equipment further comprises a duplex filter 106 connecting the transmitter 113 and the multiband receiver 104 to the antenna combination unit 101. The receiver 104 is used to receive signals in several different frequency bands for different types of mobile telephone systems that are within the Radio Frequency (RF) region. Different types of mobile telephone systems may also have different channel spacing. These mobile telephone systems may be, for example, AMPS with a channel spacing of 30KHz in the frequency band 869-894MHz and PCS with a channel spacing of 200KHz in the frequency band 1930-1990 MHz.

Signals of other mobile telephone systems in other frequency bands, using other frequency intervals, may of course also be received if the receiver comprises units suitable for these systems. Where the receive chain is suitable for, for example, AMPS and PCS1900, a choice can be made between receiving signals for both systems. The selection may be manual or automatic. For example, the system with the greatest signal-to-noise ratio at a given time may be connected.

Since the frequency bands of the received signals are different in the two systems, the antenna 100 has to be adapted to the frequency bands of these systems. This is achieved by an antenna combination unit 101 connected to the antenna 100. The antenna combining unit 101 also functions as a switch. The received RF signal is either fed to a first input of the inventive multiband receiver 104 via the switch 102 and the band-pass filter 103 or to a second input via the duplex filter 106. The two inputs are used for inputting RF signals.

As an example, assume that the device shown in fig. 1 is currently tuned for use in the system PCS 1900. Then, the antenna 100 is adjusted by the antenna combining unit 101, and can transmit and receive in the 1900MHz band. The antenna combination unit 101 is connected by a switch 102 to a first bandpass filter 103 (one of the switch positions shown in fig. 1). This filter filters all frequencies except the frequency band specified for PCS 1900. The multiband receiver 104 according to the invention receives at its input 108 a signal with a channel spacing of 200KHz in the 1900MHz region defined for PCS 1900. The output signal at the output 112 of the multiband receiver 104 is in the baseband frequency band specified for PCS 1900. The frequency content of the baseband frequency band is from 0Hz to half the channel spacing of the radio communication system transmitting the received RF signals. Since the channel spacing of the PCS1900 is 200KHz, the frequency content of the signal at the output 112 of the multiband receiver is 0-100 KHz. The output signal at output 112 is a signal having two baseband channels in quadrature, i.e. two signals having the same information content but being 90 ° out of phase. This concept is well known to those skilled in the art. Within the baseband unit, low pass filtering, detection, and adjacent channel suppression are performed on the received signal down-converted to the baseband frequency band.

When the switch 102 is in the other position shown in fig. 1, the output 109 of the transmitter 113 is connected to the antenna combination unit 101 in a manner commonly used in the art. Thus, the same antenna 100 is used for both transmission and reception.

The duplex filter 106 functions in the same manner as the switch 102 in the case of transmitting and receiving to another system, for example, AMPS. This serves to separate the transmitted signal from the received signal. The duplex filter 106 is connected in a conventional manner to an output 110 of a transmitter 113 and to an input 111 of the receiver 104. At input 111, the multi-band receiver of the present invention receives an RF signal from AMPS at a channel spacing of 30 KHz. Since AMPS has a channel spacing of 30KHz, the resulting signal at output 112 includes frequencies in the baseband frequency range of 0-15 KHz.

The multiband receiver 104 of the invention comprises at least two inputs 108 and 111 for receiving signals in the RF region and at least one output 112 connected to the baseband unit 105. The multiband receiver 104 further comprises elements that make it possible to connect the same output 112 to the same input of the baseband element 105. These situations will be explained in detail in connection with fig. 2.

Such a receiver need not be used with a transmitter and may constitute, for example, a separate unit in a paging system for receiving RF signals in two frequency bands.

The multiband receiver 104 may be implemented, for example, with an Application Specific Integrated Circuit (ASIC), making the size of the multiband receiver 104 small. This implementation of the inventive multiband receiver 104, in combination with the use of only one baseband unit 105, results in a smaller receiver with fewer components. The manufacturing costs of such a receiver are therefore low.

Fig. 2 illustrates an embodiment of a multiband receiver 104 constructed in accordance with the invention.

The first mobile telephone system (AMPS, NMT) has a smaller channel spacing. A signal with such a channel spacing is received at input 111 and is converted from a radio frequency band to an intermediate frequency band by a first mixing by mixer 202. The intermediate frequency signal is then demodulated in an I/Q demodulator 205, resulting in an output signal at the baseband frequency band at output 211.

The second mobile telephone system (GSM, PCS1900, DCS 1800) has a larger channel spacing than the first mobile telephone system described above. A signal having such a relatively large channel spacing is received at the input 108, and the received signal in the RF band is I/Q demodulated directly by the I/Q demodulator 213. An output signal in the baseband frequency band of the input signal of the second mobile telephone system is obtained at an output 214. The outputs 211, 214 are both connected to a common output 215, and the output 215 is connected to an amplifier 216. The resulting signal at output 211, 214 is thus amplified by amplifier 216 to form an amplified signal at its output 112 (fig. 1). This output includes a pair of output terminals 227, 228 as shown in fig. 2.

The input 111 is an input of a first amplifier 200 within the multiband receiver 104. The amplifier 200 mainly amplifies a signal in a radio frequency band. The amplifier 200 may be followed by a filter 201 which allows only signals in the current radio frequency band to pass. For example, for AMPS, filter 201 is a band pass filter having a pass band of 869 and 894MHz (i.e., 25MHz bandwidth).

A mixer 202 is connected downstream of the filter 201. The mixer 202 receives the filtered RF signal from the filter 201 and a signal having a predetermined frequency LOf1 from the voltage controlled oscillator VCO, thereby generating a signal in an intermediate frequency band. This intermediate frequency band is approximately 78MHz for AMPS and NMT. The pass band of filter 201 corresponding to NMT is 935-960 MHz.

For example, for AMPS, the voltage controlled oscillator generates a frequency LOf1 within the frequency range 947-; whereas for NMT a frequency LOf1 in the frequency range 1013-.

The mixer 202 is followed by a third band-pass filter 203. This filter 203 removes all frequencies in the if band signal that do not contain any information useful to the receiver, e.g. strong interference signals of other channels. As an example, for AMPS, filter 203 is designed to have a center frequency of 78MHz and a bandwidth of + -15 KHz; and for NMT the corresponding center frequency is 78MHz with a bandwidth of ± 12.5 KHz.

The filter 203 is followed by an I/Q demodulator 205. The I/Q demodulator 205 comprises a differential amplifier 204, two mixers 206, 207 and a phase shifter 208. The differential amplifier 204 differentiates the intermediate frequency signal from the filter 203. And obtaining a signal with a better signal-to-noise ratio through difference. An oscillator 212 generating a signal with a frequency LOf2 is connected to the phase shifter 208 and the mixer 207. As an example, for AMPS and NMT, the frequency LOf2 is 78 MHz.

The phase shifter 208 may be, for example, a passive network that shifts the phase of the signal generated by the oscillator 212. The phase shifted signal is mixed with the differential amplifier differential signal to produce a baseband band signal Ia at the output 209 of the I/Q demodulator 205. The signal generated by the oscillator 212 is mixed with the differential signal from the differential amplifier to obtain a signal Qa of another baseband frequency band at the output 210. Signals Ia and Qa are two baseband channels in quadrature, comprising one half of the frequency interval from zero to the system mixing the RF signal from the RF section to the baseband frequency section. The above-described I/Q demodulation is well known to those skilled in the art.

The outputs 209, 210 are connected to the inputs 226, 225, respectively, of the amplifier 216. The signal Ia is amplified by at least one amplifier 223, which may be, for example, an operational amplifier. This amplifier is connected as a voltage follower, which receives an output signal I at the output 228. Similarly, an output signal Q is obtained at the output 227 by amplifying the signal Qa. Outputs 227 and 228 are labeled as output 112 in fig. 1.

In another sublink, which receives signals belonging to another system, the input 108 is the input of an amplifier 224, which amplifies the RF signal. The amplifier 224 is a component within the second I/Q demodulator 213 which further comprises two mixers 220, 221 and a phase shifter 222. The oscillator 219 generates a signal at a frequency of LOf3, which is provided to the I/Q demodulator 213. As an example, for PCS1900, oscillator 219 generates a frequency in the frequency range 1930-1990MHz, while for DCS1800 the corresponding frequency range is 1805-1880 MHz.

The I/Q demodulator 213 mixes the signal received at the input 108 with a signal having a frequency of LOf3, as described above for the I/Q demodulator. Thus, a baseband signal Id is obtained at output 217 and a baseband signal Qd is obtained at output 218. The signals Id and Qd occupy a larger baseband frequency range than the signals Ia and Qa. In this case, it is not necessary to mix the signal from RF to IF, nor to configure filters corresponding to the additional filters 201, 203 in the first sublink. As an example, for PCS1900, this means mixing directly from the 1900MHz RF band to the 0-100KHz baseband band.

These amplifiers used in the invention may be, for example, operational amplifiers with a predetermined amplification amount, or may be connected in the form of voltage followers.

If the multiband receiver 104 of the invention can be implemented as an ASIC, some elements belonging to the transmitter can also be implemented as an ASIC. In this case, more space can be saved, allowing the RF equipment to be made smaller.

Of course, the invention is not limited to only two sublinks, but can be implemented in new ways with more than two sublinks.

Claims (17)

1. A receiving device for receiving radio frequency signals (RF signals) in a first frequency band and a second frequency band (FB1, FB 2.), said signals in the first frequency band constituting communication signals of a certain radio system (NMT, AMPS) with small channel spacing and signals in the second frequency band constituting communication signals of a certain second radio system (PCS1900, DCS1800, GSM) with large channel spacing, said receiving device being characterized in that it comprises:

a) a receiver (104) having at least a first sub-link and a second sub-link corresponding to said first and second frequency bands, respectively;

b) an adaptation unit (101) for providing an incoming signal in a first or second frequency band to a first or second sub-link of a receiver (104) depending on which system the incoming signal belongs to;

c) the first sub-link of the receiver (104) comprises:

c1) -mixing means (202) for converting the RF signals into respective IF signals and at least one first and one second filtering means (201, 203) having a bandwidth corresponding to said first frequency band (FB 1);

c2) a first demodulating means (205) for demodulating said IF, having a pair of first outputs (209, 210) for supplying quadrature components (Ia, Qa) of the demodulated IF signal at a first baseband, and

d) said second sublink comprises a second demodulating means (213) for demodulating said RF signal, having a pair of second outputs (217, 218) for presenting quadrature components (Id, Qd) of the demodulated RF signal at a second baseband; and

e) means (216) for connecting said first and second output pairs to a common receiver output (112).

2. A receiving device according to claim 1, characterized in that:

said conversion in the mixing means (202) according to c1) is carried out by mixing the received RF signal with a first mixing signal (LOf1), said first mixing signal (LOf1) being generated by a first oscillator (VCO) arranged specifically for generating mixing signals (LOf1) for said first radio system (AMPS, NMT).

3. A receiving device according to claim 2, characterized in that:

the IF signal obtained by mixing the received RF signal with the mixing signal (LOf1) has a carrier frequency of 78 MHz.

4. A receiving device according to claim 2, characterized in that:

the oscillator (VCO) generates a mixing signal (LOf1) in the frequency range equal to 947-972MHz, the mixing signal being dedicated to RF signals in the frequency range equal to 869-894 MHz.

5. A receiving device according to claim 2, characterized in that:

the oscillator (VCO) generates a mixing signal (LOf1) in the frequency range equal to 1013-.

6. A receiving device according to claim 1, characterized in that:

said first filtering means (201) is a band-pass filter having a passband equal to said first frequency band (FB1), and said second filtering means (203) is a band-pass filter having a bandwidth equal to ± 1/2 of the channel spacing of said first radio system (AMPS, NMT), with a center frequency corresponding to the carrier frequency specified for the IF signal.

7. A receiving device according to claim 6, characterized in that:

the first filtering means (201) is a band-pass filter with a pass-band equal to 869-894MHz, and the second filtering means (203) is a band-pass filter with a center frequency of 78MHz and a bandwidth of + -15 KHz.

8. A receiving device according to claim 6, characterized in that:

the first filtering means (201) is a band-pass filter with a passband equal to 935-960MHz and the second filtering means (203) is a band-pass filter with a center frequency of 78MHz and a bandwidth of + -12.5 KHz.

9. A receiving device according to claim 1, characterized in that:

according to c2), the demodulation by the first demodulation means (205) is carried out using a second mixing signal (LOf2), which second mixing signal (LOf2) is generated by a second oscillator (212) having a frequency corresponding to the carrier frequency determined for the IF signal.

10. A receiving device according to claim 9, characterized in that:

according to c2), the demodulation by the first demodulation means (205) is carried out using a second mixing signal (LOf2) having a frequency of 78 MHz.

11. A receiving device according to claim 10, characterized in that:

the baseband of said quadrature component (Ia, Qa) obtained from the first demodulation means (205) is in the frequency range between zero and a value corresponding to half the channel spacing of said first radio system (AMPS, NMT).

12. A receiving device according to claim 11, characterized in that:

the base band of the first radio system is in a frequency range equal to 0-15 KHz.

13. A receiving device according to claim 1, characterized in that:

the demodulation according to d) is carried out by the second demodulation means (213) using a third mixing signal (LOf3) generated by a third oscillator (219) in a frequency range corresponding to the second frequency band (FB 2).

14. A receiving device according to claim 13, characterized in that:

the baseband of the quadrature component (Id, Qd) obtained from the second demodulation means (213) is in a frequency range from zero to a value corresponding to one-half of the channel spacing of the second radio system (PCS1900, DCS1800, GSM).

15. A receiving device according to claim 14, characterized in that:

the base band of the second radio system is in a frequency range equal to 0-100 KHz.

16. A receiving device according to claim 1, characterized in that:

said means (216) configured according to step e) comprises a circuit arrangement consisting of at least a first and a second amplifier (223) for the quadrature components (Ia, Id, Qa, Qd), respectively.

17. A receiving device according to any preceding claim, wherein:

the adaptation means (101) are formed by an antenna combination unit.