JP3435330B2 - Receiver having multi-rate transmission function - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver, and more particularly to a receiver having a multi-rate transmission function for communicating in a plurality of bandwidths.

[0002]

2. Description of the Related Art With the spread of mobile communication systems in recent years,
Demand for mobile communication terminals is increasing. At the same time, the content of communication, which has conventionally been limited to voice communication, has been diversified into data and fax transmission, and even image communication. In order to deal with these diversified communication contents, it is necessary to add a multirate transmission function to the system. That is, it is a function that realizes efficient transmission of various data by making the bandwidth variable.

Conventionally, this type of receiver has been constructed as shown in FIG. In FIG. 21, the receiver includes, for example, a frequency conversion unit 2 that converts the frequency of a signal received by the antenna 1 and the like, a synthesizer 3 that outputs a predetermined frequency to the frequency conversion unit 2, and first to nth intermediate frequencies. Filter (hereinafter referred to as IF filter if necessary) 4
a first filter means 4 having a to 4n in multiple stages;
Switch 5A provided in front of first filter means 4
And a switching means 5 including a switch 5B provided in the latter stage, and first and second switches provided in the latter stage of the switch 5B.
Quadrature demodulator 6 having quadrature demodulators 6a and 6b
A second filter means 7 having first and second baseband filters 7a and 7b, and first and second
A / D converter means 8 having A / D converters 8a and 8b, output terminals 9A and 9B, and switches 5A and 5B.
And a system band switching signal generating unit 10 for supplying a system band switching signal to the second filter unit 7.

Next, the basic operation of the conventional receiver will be described with reference to the drawings.

The high frequency signal input to the frequency conversion means 2 is converted into an intermediate frequency signal (hereinafter referred to as an IF signal) having a predetermined frequency in the frequency conversion means 2 and output. The intermediate frequency (hereinafter, I
The signal (denoted as F) is input to any of the IF filters 4a to 4n. Here, the IF filters 4a to 4n
Are provided for each of the plurality of bandwidth types of the transmitted signal. Also, the IF filters 4a to 4
n is configured to be switched to any one by the switch switching means 5 controlled by the system band switching signal.

The IF signal filtered by any one of the filters 4a, 4b, 4c or 4n of the first filter means 4 switched by the switching means 5 is input to the quadrature demodulation means 6 and the quadrature demodulation means 6 It is converted into baseband signals of I channel and Q channel and output.

The output signal of the quadrature demodulation means 6 is input to the second filter means composed of the baseband filters 7a and 7b. The baseband filters 7a and 7b are low-pass filters that can change the cutoff frequency according to the switching signal output from the system band switching signal generation means 10. The baseband signal filtered by the second filter means 7 is input to the first and second A / D converters 8a and 8b of the A / D conversion means 8 and converted from an analog signal to a digital signal. . Thereafter, the digital signal is output via the output terminals 9a and 9b and demodulated by a demodulator (not shown).

The synthesizer 3 oscillates a local oscillation frequency such that the center frequency of the desired signal included in the input signal is frequency-converted to match the frequency of the predetermined IF signal, and the output of the synthesizer 3 is generated. Is supplied to the frequency conversion means 2. At this time, the oscillation frequency of the synthesizer 3 is controlled by a control signal (not shown). That is, the oscillation frequency f _LO of the synthesizer 3 is, for example, a frequency of a difference f _RF −f _IF between the center frequency f _{RF of the} desired signal and the frequency f _IF of the predetermined IF signal.

When signals of a plurality of transmission rates are received by using the conventional receiver having the above-mentioned structure, first, (1) the switching means 58 is used to switch the first filter means 4 by the system band switching signal. The IF filters 4a to 4n are switched to ones suitable for a desired bandwidth, (2) the bandwidths of the baseband filters 7a and 7b of the second filter means 7 are changed to appropriate values, and (3) The synthesizer 3 is caused to oscillate the local oscillation frequency described above.

The above operation will be described below by showing concrete numbers. Now, assume that the system bandwidth can be selected from the minimum bandwidth and a bandwidth that is an integral multiple thereof. For example, the system bandwidth is 5MHz, 10MH
z and 20 MHz. Carrier frequency is 2GH
The z-band and system bandwidth are set to 60 MHz, and FIG. 22 shows a state in which the signals of the plurality of bandwidths are assigned.

The structure of a conventional receiver whose IF is designed to be 200 MHz is as follows. Assuming that the first filter means 4 has a wider bandwidth in the order of the IF filters 4a, 4b, 4c, the IF filter 4a has a bandwidth of 5 MHz.
Center frequency 200 MHz, IF filter 4b has a bandwidth of 10 MHz, center frequency 200 MHz, IF filter 4
c is a bandpass filter having a bandwidth of 20 MHz and a center frequency of 200 MHz. IF filter 4a
23 (a) shows the respective frequency characteristics of FIG.
Shown in (b) and (c).

Next, the operation when receiving a plurality of rates will be described. First, when a signal having a center frequency of 2000 MHz is received during transmission at the maximum bandwidth of 20 MHz, (1) First, the switching means 5 causes the first filter means 4 to operate.
Is switched to the third IF filter 4c, (2) the cutoff frequency of the second filter means 7 is set to 10 MHz, and (3) the oscillation frequency of the synthesizer 3 is 2000 MHz, which is the center frequency of the input signal, and IF. 200M
The difference from Hz, that is, 1800 MHz. By operating as described above, a signal having a center frequency of 2000 MHz and a bandwidth of 20 MHz is received. The frequency characteristic of the third IF filter 4c at this time is shown in FIG. 23 (c). The frequency characteristics of the baseband filters 7a and 7b of the second filter means 7 are shown in FIG. 24 (a).

When a signal having a center frequency of 1972.5 MHz is received during transmission at the minimum bandwidth of 5 MHz, (1) the switching means 5 causes the IF of the first filter means to be used.
Switching to the filter 4a, (2) the cutoff frequency of the baseband filters 7a and 7b of the second filter means 7 is 2.5 MHz, and (3) the oscillation frequency of the synthesizer 3 is 1972.5 MHz which is the center frequency of the input signal. And I
The difference with F which is 200MHz, that is, 1772.5M
Hz. By operating as described above, a signal having a center frequency of 1972.5 MHz and a bandwidth of 5 MHz is received. The frequency characteristic of the IF filter 4a at this time is shown in FIG.
3 (a). The frequency characteristics of the baseband filters 7a and 7b are as shown in FIG. 24 (b).

Although the description of other cases is omitted here, the first filter means 4 including the multistage IF filters 4aA to 4n and the baseband filters 7a and 7a.
A method of receiving by the same configuration operation as above by switching the bandwidth of the second filter means 7 including b and setting the oscillation frequency of the synthesizer 3 to a frequency at which the desired signal exactly matches the IF frequency. Are the same.

As described above, the conventional receiver of this type supports the multi-rate transmission by changing the bandwidths of the IF filter and the base band filter and the oscillation frequency of the synthesizer by the control signal. .

In a receiver used for a mobile communication terminal or the like, the IF filter is usually a passive filter. A typical IF filter is a surface acoustic wave (SA
W-Surface Acoustic Wave-) is used.
This type of filter is not suitable for miniaturization because the operating frequency is determined by its physical size. However, in the above receiver, it is necessary to prepare the IF filters for a plurality of transmission rates. For example, when the system uses four types of transmission bandwidths, it is necessary to prepare four IF filters in total. As described above, when the filters are provided in multiple stages, a plurality of filters are required and the circuit configuration of the filter means cannot be integrated into a circuit, which is a serious obstacle to downsizing of the device.

Further, in the system in which the required bandwidth is selected from the minimum bandwidth and the bandwidth which is an integral multiple thereof as described above, the frequency interval in the carrier of the received signal is 1 / the minimum bandwidth. Therefore, the synthesizer 6 needs to have a function of oscillating at a frequency interval of 1/2 of the minimum bandwidth. For example, in the above example, the synthesizer 6 needs to have a function of oscillating at a frequency interval of 2.5 MHz which is 1/2 of the narrowest bandwidth of 5 MHz. Generally, in a synthesizer, the phase noise characteristic deteriorates as the oscillation frequency interval becomes narrower with respect to the center frequency of the oscillation frequency range. Therefore, the synthesizer used for the receiver having the multi-rate transmission function will function in a state in which the phase noise characteristic is deteriorated even when the bandwidth of the signal to be processed is the widest, and the reception characteristic is deteriorated. It had the problem of being lost.

[0018]

A receiver having a multi-rate transmission function according to the present invention has been made in order to eliminate the above problems, and the first filter means is composed of one intermediate frequency filter. By doing so, it is an object of the present invention to provide a receiver having a multi-rate transmission function, which can be integrated into a circuit, can be simplified in configuration, and can be manufactured at low cost.

Further, the oscillation frequency interval of the synthesizer is
Since it is necessary to set the interval when the bandwidth is the narrowest, there is a problem that the phase noise characteristic is poor.
Therefore, it is another object of the present invention to eliminate this problem and provide a receiver having a multirate transmission function in which the synthesizer has a wide oscillation frequency interval.

[0020]

In order to achieve the above object, a receiver having a multirate transmission function according to a first aspect of the present invention comprises a frequency conversion means for converting a received high frequency signal into an intermediate frequency, and this frequency conversion. a first filter means connected to the output terminal means, and the first connection quadrature demodulation means to the output end of the filter means, first connected to the output terminal of the quadrature demodulation means <br/> 2 Filter means and this second
And A / D conversion means connected to the output terminal of the filter means, and the plurality of bandwidths used are the minimum transmission bandwidth.
In a receiver having a multi-rate transmission function used in a wireless communication system that performs communication using a plurality of signal bandwidths that are integer multiples of the bandwidth , the first filter means includes the frequency conversion means. The widest and narrowest signal bandwidth among the plurality of signal bandwidths supplied.
One bandpass filter having a bandwidth corresponding to the sum of the signal bandwidths is provided.

Further, a receiver having a multi-rate transmission function according to claim 2 is the receiver according to claim 1, wherein the second filter means performs communication using the widest signal bandwidth. In the first filter means
The signal bandwidth is wider than the signal bandwidth of , and functions as a low-pass filter with a cutoff frequency having the widest signal bandwidth , and when the communication is performed using the narrow signal bandwidth , the communication is performed. The feature is that it functions as a bandpass filter for the signal bandwidth .

A receiver having a multi-rate transmission function according to a third aspect is the receiver according to the first aspect, further comprising a synthesizer for generating a local signal having a predetermined frequency and supplying the local signal to the frequency converting means. An interval of the predetermined frequency of the local signal generated by the synthesizer is twice the narrowest signal bandwidth .

According to a fourth aspect of the present invention, there is provided a receiver having a multi-rate transmission function, the frequency converting means for converting a received high frequency signal into an intermediate frequency, and the first filter means connected to the output end of the frequency converting means. A quadrature demodulation means connected to the output end of the first filter means, and a second filter means connected to the output end of the quadrature demodulation means ,
A / D conversion means connected to the output terminal of the second filter means, and a plurality of used bandwidths have the minimum transmission.
In a receiver having a multi-rate transmission function used in a wireless communication system that performs communication using a bandwidth and a plurality of signal bandwidths that are integral multiples thereof , the first filter means includes the frequency conversion means. of the plurality of signal bandwidth supplied through the most the maximum transmission bandwidth of the bandwidth of wide signal which has as its pass band width, the carrier frequency of the widest signal bandwidth, the first It is characterized by including one band-pass filter controlled to have the center frequency of the pass band width of the filter means.

Further, the receiver having a multi-rate transmission function according to claim 5, in the receiver according to claim 4, when performing communication using a maximum transmission signal bandwidth,
The second filter means has a bandwidth of half the bandwidth.
When a communication is performed using the minimum transmission signal bandwidth , the second filter means functions as a low-pass filter having a cut-off frequency set so that the second filter means passes the bandwidth. as a filter
It is characterized by functioning .

A receiver having a multi-rate transmission function according to a sixth aspect is the receiver according to the first or fourth aspect, wherein the second filter means has a cutoff frequency used for communication. It is composed of a low-pass filter selected according to the bandwidth to be used .
It

A receiver having a multi-rate transmission function according to a seventh aspect is the receiver according to the sixth aspect, wherein the second filter means includes a switched capacitor filter, and the low-pass filter is cut. characterized in that off frequency is determined by the cutoff frequency of the switched capacitor filter.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of a receiver having a multirate transmission function according to the present invention will be described in detail with reference to FIGS. First,
A receiver having a multi-rate transmission function according to the first embodiment will be described with reference to FIG. In the system for performing communication with a plurality of bandwidths to which the receiver according to the first embodiment is applied, a plurality of transmission bandwidths used are a minimum transmission bandwidth Δf1 and a bandwidth that is an integral multiple thereof. is there.

FIG. 1 is a block diagram showing the configuration of a receiver having a multi-rate transmission function according to the first embodiment of the present invention. In FIG. 1, the receiver is a radio frequency signal input from an antenna 1 or the like. Frequency conversion means 2 for frequency-converting the high-frequency signal, a synthesizer 3 for supplying a local oscillation signal of a predetermined frequency to the frequency conversion means 2, and one intermediate frequency (hereinafter, IF-Intermediate Frequency-)
First filter means 4 composed of a filter 40
And quadrature demodulation means 6 comprising first and second quadrature demodulators 6a and 6b for respectively demodulating the in-phase (I) component and the quadrature (Q) component of the output of the first filter means 4, and the respective components. First and second to pass the base frequency of
Second filter means 7 composed of baseband filters 7a and 7b, and A / D conversion means composed of first and second A / D converters 8a and 8b for converting analog signals of respective components into digital signals. 8 and a system band switching signal generation unit 7 that outputs a system band switching signal to the second filter unit 7. Other components than the configuration of the first filter means 4 are shown in FIG.
Since it has the same function as the constituent element of the conventional receiver described using No. 1, duplicate description will be omitted.

[0029] Here, the center frequency that can take the desired signal input through the antenna 1 _{f RF1, f RF2,}
..., f _RFn (n is an integer, and f _RF1 <f _RF2 <... <
f _RFn ). In this case , the narrowest transmission bandwidth is Δ
If f1 (for example, 5 MHz in FIG. 8 to be described later) is set, the difference between adjacent center frequencies among the center frequencies that can be obtained by the desired signal input from the antenna is ½ of the narrowest transmission bandwidth Δf1 (for example, In the case of FIG. 8 described later, f
The difference between _RF2 and _fRF1 is 1/2 of 5 MHz, which is 2.5.
MHz) . That is, “f _{RF (i + 1)} −f
_RFi = Δf1 / 2 (i is an integer) ”. Further, a predetermined intermediate frequency (IF) is set to f _IF, and the oscillation frequency generated by the synthesizer 3 is set to f _LO1 , f
_LO2 , ..., f _LOm (m is an integer, and f _LO1 <f
_LO2 <... <f _LOm ).

A portion having a characteristic function of the first embodiment will be described below. First, the intermediate frequency (IF) filter 40 that constitutes the first filter means 4 is a bandpass filter having a sum bandwidth of the widest bandwidth and the narrowest bandwidth among the plurality of transmission bandwidths. In addition, the baseband filter 7 that constitutes the second filter means 7
It is the same as the conventional receiver that the frequency characteristics of a and 7b are made variable by the control signal, but the conventional receiver changes the cut-off frequency by the control signal, so that the characteristics are always low-pass characteristics. It was On the other hand, this first
As the baseband filter in the receiver according to the embodiment, a baseband filter that can change not only the cutoff frequency but also the type of filter such as lowpass characteristic or bandpass characteristic is used.

Further, in the first embodiment of the present invention, f _{LO (i + 1)} -f _LOi = 2Δf1 (i is an integer) and the oscillation frequency of the synthesizer 3 are controlled by controlling the synthesizer 3 as follows. Is twice the narrowest transmission bandwidth.

As shown in FIG. 2, the lowest local frequency f _LO1 generated in the synthesizer 3 is f _LO1 = f _RF1
-F _IF . At this time, if the bandwidth of the desired signal is the narrowest, the oscillation frequency of the synthesizer 3 is such that the center frequency of the desired signal output from the frequency conversion means 2 matches a predetermined IF frequency, or Controlled to offset the frequency with the narrowest bandwidth,
Also, if the bandwidth of the desired signal is wider than that,
The oscillating frequency of the synthesizer 3 is controlled so that the center frequency of the output signal of the frequency converting means 2 is offset from a predetermined IF frequency by ½ of the narrowest bandwidth Δf1 of the transmission bandwidth.

Next, the operation of the receiver having the multi-rate transmission function according to the second embodiment as the first specific example of the first embodiment of the present invention will be described.

The high frequency signal f input to the frequency converter 1
_RF is converted to an IF signal by the frequency conversion means 2 and output, and the output IF signal of the frequency conversion means 2 is input to the IF filter 40. At this time, the frequency conversion means 2
In the input high frequency signal f _RF , the center frequency of the desired signal frequency-converted at the output of the frequency conversion means 2 by the local signal supplied from the synthesizer 3 is higher than the predetermined IF frequency f _IF . The band of the IF filter 40 is set so as to have the sum of the widest bandwidth and the narrowest bandwidth, although the frequency shifts, so that the band limitation is performed without removing the desired signal component. The IF signal band-limited by the IF filter 40 is input to the quadrature demodulation means 6, converted into I-channel and Q-channel baseband signals by the first and second quadrature demodulators 6a and 6b, and output. The output signals of the quadrature demodulators 6a and 6b are input to the first and second baseband filters 7a and 7b. The baseband filters 7a and 7b can change the low-pass / band-pass characteristics and their cutoff frequencies according to the switching signal generated by the system band switching signal generating means 10.

The baseband signals band-limited by the baseband filters 7a and 7b are the first and second A / D signals.
The signals are input to the converters 8a and 8b and converted into digital signals. Thereafter, the digital signal is demodulated by a demodulator (not shown). As described above, according to the configuration of the present invention, the frequency interval of the local signals oscillated by the synthesizer 3 is 1/2 the frequency interval of the narrowest transmission bandwidth in the related art. It can be expanded by 4 times. Therefore, the phase noise characteristic of the synthesizer 3 can be reduced, and a receiver having a multi-rate transmission function with good reception characteristics can be realized.

The receiver according to the second embodiment will be described below with reference to specific numbers. The system assumed here is the same as the system given for the conventional receiver. That is, the system bandwidth is 5 MHz, 10 MH
z, 20MHz, carrier frequency is 2GHz
It is assumed that the band and the system bandwidth are 60 MHz and signals are assigned as shown in FIG. 22, for example.

Further, as shown in FIG. 3, the synthesizer 3
As the lowest frequency of “ f _LO1 = f _RF3 −f _IF ”
If " f _{LO (i + 1)} -f _LOi = 2Δf1 " is selected,
The oscillating frequency that can be output by the synthesizer 3 is 10 MHz, and the oscillating frequency is 1777,5 MHz, 1787.5 MH.
z, 1797.5 MHz, 1807.5 MHz, 181
It becomes 7.5 MHz and 1827.5 MHz.

Although the intermediate frequency (IF) is 200 MHz as in the conventional receiver, the IF filter 40 is different from the conventional 20 MHz in that the bandwidth is the maximum transmission bandwidth 20 MHz and the minimum transmission bandwidth 5 MHz of the system. A bandpass filter having a sum of 25 MHz and a center frequency of 200 MHz is used. The local oscillation frequency supplied to the quadrature demodulator 6 is set to, for example, the lower limit frequency of the pass band of the IF filter 40, that is, 187.5 MHz.

The operation at the time of receiving a plurality of rates will be described. First, when receiving a signal having a center frequency of 2000 MHz during transmission of the maximum bandwidth of 20 MHz, the synthesizer 3 is selected so as to output a local oscillation signal of 1797.5 MHz. As a result, the IF signal output from the frequency conversion means 2 becomes as shown in FIG. 4, and the baseband signal becomes as shown in FIG. Here, the characteristic of the baseband filter 7 is that the center frequency is 15 MHz and the bandwidth is 10
If a bandpass filter of MHz is used, the output of the baseband filter 4 is as shown in FIG. By operating in this way, the center frequency is 2000 MHz and the bandwidth is 20 MH.
z signal is received.

When the center frequency of the signal having the maximum bandwidth of 20 MHz is 1995 MHz, the IF signal output from the frequency converter 1 is as shown in FIG. 7, and the baseband signal is as shown in FIG. Therefore, assuming that the characteristics of the baseband filters 7a and 7b are bandpass filters having a center frequency of 10 MHz and a bandwidth of 20 MHz, the outputs of the baseband filters 7a and 7b are as shown in FIG. By operating in this way, the center frequency 199
A signal of 5 MHz and a bandwidth of 20 MHz will be received.

Next, a case where the transmission bandwidth is 10 MHz will be described. For example, when the carrier wave receives a signal of 2025 MHz, the frequency of the local oscillation signal transmitted by the synthesizer 3 is selected to be 1827.5 MHz.

As a result, the IF signal output from the frequency conversion means 2 becomes as shown in FIG. 10, and the baseband signal becomes as shown in FIG. Here, the baseband filters 7a and 7b in the second filter means 7
If the characteristic of is a bandpass filter having a center frequency of 10 MHz and a bandwidth of 10 MHz, the baseband filter 7a,
The output of 7b is as shown in FIG. By operating as described above, the center frequency is 2025 MHz and the bandwidth is 10M.
Receive the Hz signal.

Further, in this case, as shown in FIG. 10, signals of other systems are also mixed in the band of the IF filter 40.
When the power of the signal of the other system to be mixed is very high, distortion may be generated in the quadrature demodulation means 6 and the baseband filter section of the second filter means 7. Therefore, the local oscillation frequency of the synthesizer 3 is set to 1817. By setting the frequency to 0.5 MHz, it is possible to prevent signals from other systems from being mixed as shown in FIG. At this time, although not shown, the characteristics of the baseband filters 7a and 7b may be bandpass filters having a center frequency of 20 MHz and a bandwidth of 10 MHz. By operating as described above, it is possible to receive a signal having a center frequency of 2025 MHz and a bandwidth of 10 MHz.

Next, the case where a signal having a transmission bandwidth of 5 MHz is received will be described. For example, if the carrier wave is 1987.
When receiving a signal of 5 MHz, the local oscillation frequency of the synthesizer 3 is 1787.5 MHz. In this case, since the local oscillation frequency is 1787.5MHz, the carrier frequency of the desired signal will be frequency converted to 200 MHz. Since the local oscillation frequency applied to the quadrature demodulation means 6 is set to 187.5 MHz , the output of the quadrature demodulation means 6 has a center frequency of 12.5 MHz and a bandwidth of 5 MHz as shown in FIG. Become a signal. At this time, the baseband filter 7 of the second filter means 7
a and 7b have a center frequency of 12.5 MHz and a bandwidth of 5M
To act as a Hz bandpass filter is set by the switching signal supplied from the system band switching signal generating means 10. By operating as described above, it is possible to receive a signal having a center frequency of 1987.5 MHz and a bandwidth of 5 MHz.

As described above, the interval between the oscillation frequencies of the synthesizer 3 is half the frequency interval of the narrowest transmission bandwidth in the past, but the maximum bandwidth of the IF filter is transmitted as in the present invention. By setting the bandwidth to be equal to or more than the sum of the bandwidth and the minimum transmission bandwidth, the oscillation frequency interval of the synthesizer 3 can be extended to twice the narrowest transmission bandwidth, which is four times the conventional one. Therefore, the phase noise characteristic of the synthesizer 3 can be reduced, and a receiver having a multi-rate transmission function with good reception characteristics can be realized.

In the above first and second embodiments, the local oscillation frequency applied to the quadrature demodulating means 6 is fixed at 187.5 MHz, so that the baseband filter needs to change its bandwidth and center frequency by bandpass. There was,
As in the receiver according to the third embodiment shown in FIG. 15, the synthesizer 11 and the phase shifter 12 are used, and the local oscillation frequencies are 195 MHz, 197.5 MHz, 200 MHz, 20.
By giving 2.5MHz and 2.5MHz intervals,
As shown in FIGS. 16 (a), (b) and (c) corresponding to the respective transmission bandwidths of 20 MHz, 10 MHz and 5 MHz, the low frequency component of the signal frequency-converted by the output of the orthogonal demodulation means 6 is cut. It is also possible to have low-pass characteristics and not have band-pass characteristics.

The synthesizer 11 has the same 2.5 as the conventional one.
It is necessary to oscillate at a frequency interval of 2 MHz, but the synthesizer 11 operates at a frequency of 2.
Since it is sufficient to oscillate at intervals of 5 MHz, the phase noise characteristic can be reduced, and a receiver having a multi-rate transmission function with good reception characteristics can be realized.

The base band filter at this time is 20M.
A low-pass filter having a cutoff frequency of about 1/2 of each transmission bandwidth of Hz, 10 MHz, and 5 MHz may be used. This low-pass filter is configured by, for example, a folding distortion removal filter 13 and a switched capacitor filter (SCF) 14 as shown in FIG. 17, so that the clock frequency applied to the SCF 14 is selected by a system band switching signal. The cutoff frequency can be easily selected. In addition, the aliasing removal filter 1
The cutoff frequency of 3 may be set according to the maximum transmission bandwidth (10 MHz in this case), or may be switched by the system band switching signal.

Next, a fourth embodiment as a second specific example of the first embodiment will be described. In this specific example, the center frequency when the bandwidth is 20 MHz is 1980 MHz 2000 MHz 2020 MHz as shown in FIG. 18A, and when the bandwidth is narrower than that, it is 20 MHz.
18B, the center frequency when the bandwidth is 10 MHz is set to 1975 MHz 1985 MHz 1995 MHz 2005 MHz 2015 MHz 2025 MHz, as shown in FIG. 18B. As shown in FIG. 18C, the center frequency when the bandwidth is 5 MHz is 1972.5 MHz 1977.5 MHz 1982.5 MHz 1987.5 MHz 1992.5 MHz 1997.5 MHz 2002.5 MHz 2007.5 MHz 2012.5 MHz 2017. Assume a system assigned 5 MHz 2022.5 MHz 2027.5 MHz. In this case,
IF filter 2 bandwidth maximum transmission bandwidth than, for example, a 20 MHz, the local oscillation frequency to be applied to the orthogonal demodulating means 6 and 200 MHz, 1780MHz frequency that obtained output of the synthesizer 3, 1800 MHz, 18
It is set to 20 MHz, and the oscillation frequency of the synthesizer 3 is controlled so as to match the center frequency of the widest band channel including the desired signal.

The operation of the fourth embodiment will be specifically described below. If you want to receive the widest bandwidth signal,
The frequency conversion means and the quadrature demodulation means perform frequency conversion so that the center frequency of the desired signal becomes 0 Hz, and the baseband signal is received by quadrature demodulation.
In this case, the operation is the same as that of the conventional receiver. If the band is narrower than that, frequency conversion is performed using a local oscillation frequency such that the center frequency of the widest channel including the desired band is converted to 0 Hz by the frequency conversion means and the quadrature demodulation means. Moreover, unnecessary signal components are cut and demodulated by setting the characteristic of the baseband filter to a bandpass characteristic that allows only a desired signal to pass.

First, when a signal having a center frequency of 1980 MHz is received during transmission of the maximum bandwidth of 20 MHz, the characteristic of the baseband filter 7 is a low-pass filter with a cutoff frequency of 10 MHz, and the oscillation frequency of the synthesizer 3 is the input signal. The center frequency is 1980 MH
The difference between z and IF which is 200 MHz, that is, 1780
MHz. At this time, the frequency characteristics of the baseband filters 7a and 7b of the second filter means 7 are shown in FIG.
It is the same as that shown in (a).

Next, the case where the transmission bandwidth is 10 MHz will be described. For example, when the carrier wave receives a signal of 1985 MHz, the synthesizer 3 is the same as the above-mentioned 178
0 MHz. This point is greatly different from the conventional receiver. In this case, since the local oscillation frequency is 1780 MHz, the carrier frequency of the desired signal is frequency-converted to 205 MHz, so that the output of the quadrature demodulator 6 has a center frequency of 5 MH.
At z, the bandpass signal has a bandwidth of 10 MHz. At this time, the baseband filters 7a and 7b have a center frequency of 5
It is set by the system band switching signal so that the band pass filter has a bandwidth of 10 MHz at MHz.

Next, a case where the transmission bandwidth is 5 MHz will be described. For example, when the carrier wave receives a signal of 1987. 5 MHz, the synthesizer 3 operates in the same manner as above.
80 MHz. In this case, the local oscillation frequency is 178
Since it is 0MHz, the carrier frequency of the desired signal is 207.5M.
Since the frequency is converted to Hz, the output of the quadrature demodulating means 6 becomes a bandpass signal having a center frequency of 7.5 MHz and a bandwidth of 5 MHz. At this time, the baseband filter 4 is set by the system band switching signal 7 so as to be a bandpass filter having a center frequency of 7.5 MHz and a bandwidth of 5 MHz.

As described above, in general, when a signal having the widest bandwidth is received, frequency conversion is performed so that the center frequency becomes 0 Hz, and when the bandwidth is narrower than that, the frequency conversion is performed. Frequency conversion is performed using a local oscillation frequency such that the center frequency of the widest bandwidth channel including the band is converted to 0 Hz, and the characteristics of the baseband filter are bandpass characteristics that allow only a desired signal to pass. By doing so, unnecessary signal components are cut and demodulated. As a result, in a receiver that receives signals of a plurality of bandwidths, it is possible to configure the oscillation frequency interval of the synthesizer to be wide without increasing the number of IF filters. Therefore, the phase noise characteristic of the synthesizer 3 can be reduced, and a receiver having a multi-rate transmission function with good reception characteristics can be realized.

Next, a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 19 is a block diagram showing the configuration of a receiver having a multirate transmission function according to the fifth embodiment of the present invention. In FIG. 19, the receiver includes a first frequency converter 2 as a frequency converting means, a synthesizer 3, and a first frequency converter 1.
First filter means 4 consisting of one IF filter 40
, A second frequency converter 15, a second filter means 7 including a baseband filter 70, an A / D conversion means 8, an output terminal 9, and a system band switching signal to the baseband filter 70. The system band switching signal generation means 10 is provided.

The characteristic configuration of the fifth embodiment is that the quadrature demodulating means 6 in the first embodiment is replaced with the second frequency converter 15 in the fifth embodiment. The operation of the fifth embodiment is also similar to that shown in the fourth embodiment. The difference is that in the fourth embodiment, when a signal with the widest bandwidth is received, the center frequency of the desired signal is 0 at the output stage of the orthogonal demodulation means 63.
While the local oscillation frequency is controlled so as to become Hz, in the fifth embodiment, when the signal having the widest bandwidth is received, the lower limit frequency of the desired signal is the second frequency converter 15. The local oscillation frequency is controlled so that it becomes 0 Hz in the output stage. Generally, the receiver according to the first embodiment of the present invention is called a direct conversion system, whereas the receiver according to the fifth embodiment is called a low IF system.

When receiving a signal with the widest bandwidth,
Frequency conversion is performed so that the lower limit frequency becomes 0 Hz, and the baseband signal is demodulated and received. If the band is narrower than that, frequency conversion is performed using a local oscillation frequency that is converted to the lower limit frequency 0 Hz of the channel with the widest bandwidth including the desired band, and the baseband filter By setting the characteristic to be a bandpass characteristic that allows only a desired signal to pass, unnecessary signal components are cut and demodulated.

Next, assuming the same system as the system shown in the fourth embodiment as the system of the fifth embodiment, the operation of the receiver according to the fifth embodiment at the time of receiving multiple rates will be described. To do.

First, when a signal having a center frequency of 1980 MHz is received during transmission of the maximum bandwidth of 20 MHz (the lower limit frequency of this signal is 1970 MHz and the upper limit frequency is 1990 MHz), (1) the characteristics of the baseband filter 7 Is a low-pass filter with a cutoff frequency of 20 MHz. (2) Further, the oscillating frequency of the synthesizer 3 is equal to the lower limit frequency of the input signal of 1970 MHz and IF.
The difference from 200 MHz, that is, 1770 MHz. (In the fourth embodiment, the local oscillation frequency is determined so that the center frequency of the desired signal is 200 MHz, but in the present embodiment, the lower limit frequency of the desired signal,
In other words, in this case, 200M where 1970MHz is the IF
The local oscillation frequency is determined to be Hz. ) By operating as described above, a signal having a center frequency of 1980 MHz and a bandwidth of 20 MHz is received. The frequency characteristic of the baseband filter 7 at this time is as shown in FIG.

Next, a case where the transmission bandwidth is 10 MHz will be described. For example, the carrier frequency is 1985 MHz
The local oscillation signal output from the synthesizer 3 when receiving the signal of 1 has a frequency of 1770 MHz as described above. In this case, the local oscillation frequency is 17
Since it is 70 MHz, the carrier frequency of the desired signal is 215 MH
Since the frequency is converted to z, the output of the second frequency converter 15 is not a baseband signal but a center frequency of 15M.
A signal having a bandwidth of 10 MHz at Hz is similar to the second example of the first embodiment. At this time, the baseband filter 7 has a center frequency of 15 MHz and a bandwidth of 10 MHz.
It is set by the system band switching signal generation means 10 so as to be a band pass filter. The frequency characteristic of the baseband filter 7 at this time is shown in FIG. By operating in this way, it is possible to receive a signal with a center frequency of 1985 MHz and a bandwidth of 10 MHz without changing the characteristics of the IF filter 4 and without changing the oscillation frequency of the synthesizer 3.

Next, a case where the transmission bandwidth is 5 MHz will be described. For example, the frequency of carrier wave is 1987.5 MH
When the z signal is received, the local oscillation frequency of the synthesizer is 1770 MHz as above. In this case, since the local oscillation frequency is 1770 MHz, the carrier frequency of the desired signal is frequency-converted to 217.5 MHz. Therefore, the output of the second frequency converter 15 is not a baseband signal, but a center frequency of 17.5 MHz and a bandwidth. Is a signal of 5 MHz, which is similar to the second specific example of the first embodiment. At this time, the baseband filter 7 has a center frequency of 1
The system band switching signal generation means 10 sets the band pass filter having a 7.5 MHz bandwidth of 5 MHz. The frequency characteristic of the baseband filter 7 at this time is shown in FIG. By operating in this way, it is possible to receive a signal having a center frequency of 1987.5 MHz and a bandwidth of 5 MHz without changing the characteristics of the IF filter 4 and without changing the oscillation frequency of the synthesizer 3.

As described above, when receiving a signal with the widest bandwidth, frequency conversion is performed so that the lower limit frequency is 0 Hz, and the baseband signal is demodulated for reception. If the band is narrower than that, frequency conversion is performed using a local oscillation frequency such that the lower limit frequency of the widest channel including the desired band is converted to 0 Hz, and the baseband filter By setting the characteristic to be a bandpass characteristic that allows only a desired signal to pass, unnecessary signal components are cut and demodulated.

By operating as described above, it is possible to configure the receiver for signals of a plurality of bandwidths without increasing the number of IF filters and reducing the oscillation frequency of the synthesizer. .

In each of the above embodiments, the characteristics of the IF filter 40 and the baseband filter 70 show a configuration in which the margin is not taken into consideration with respect to the system bandwidth. In actual designs, the bandwidth of the filter is often set slightly wider than the bandwidth of the desired signal. However, even in such a case, the effect that the number of IF filters can be reduced and a synthesizer having a high phase noise characteristic can be used by using the configuration method of the present invention is similar.

[0065]

As described in detail above, according to the receiver having the multi-rate transmission function of the present invention, the intermediate frequency filter which constitutes the first filter means is
In addition, a simple structure can be obtained, and the manufacturing cost can be suppressed by integrating the circuit structure of the first filter means into an integrated circuit.

Further, since the intervals of the oscillating frequencies of the synthesizer can be widened, not only the number of intermediate frequency filters can be reduced, but also the high phase noise characteristic can be greatly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a receiver having a multirate transmission function according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing characteristics of first filter means of the receiver having the multi-rate transmission function according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing frequency characteristics of a high frequency signal and a local oscillation signal of the receiver according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an output of a frequency converter when receiving a signal having a bandwidth of 20 MHz according to the second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an output of the quadrature demodulator 3 when receiving a signal having a bandwidth of 20 MHz according to the second embodiment.

FIG. 6 is an explanatory diagram showing an output of a baseband filter 4 when receiving a signal having a bandwidth of 20 MHz according to the second embodiment.

FIG. 7 is a diagram showing a configuration in which the center frequency is different in the second embodiment.
Explanatory drawing which shows the output of the frequency converter at the time of receiving the signal of the bandwidth of MHz.

FIG. 8 is a diagram showing a different center frequency according to the second embodiment.
Explanatory drawing which shows the output of the orthogonal demodulation means at the time of receiving the signal of the bandwidth of MHz.

FIG. 9 is a diagram showing a different center frequency in the second embodiment.
Explanatory drawing which shows the output of the 2nd filter means at the time of receiving the signal of the bandwidth of MHz.

FIG. 10 is an explanatory diagram showing the output of the frequency converter when receiving a signal having a bandwidth of 10 MHz according to the second embodiment.

FIG. 11 is an explanatory view showing the output of the quadrature demodulation means when receiving a signal having a bandwidth of 10 MHz in the second embodiment.

FIG. 12 is an explanatory diagram showing the output of the second filter means when receiving a signal having a bandwidth of 10 MHz according to the second embodiment.

FIG. 13 is an explanatory diagram showing the output of the frequency conversion means when a signal having a bandwidth of 10 MHz is received when the oscillation frequency of the synthesizer in the second embodiment is changed.

FIG. 14 is an explanatory diagram showing the output of the frequency conversion means when receiving a signal having a bandwidth of 5 MHz according to the second embodiment.

FIG. 15 is a block diagram showing a configuration of a receiver having a multirate transmission function according to a third embodiment of the present invention.

FIG. 16 is an explanatory diagram showing the output of the second filter means of the receiver according to the third embodiment.

FIG. 17 is a block diagram showing the configuration of a baseband filter that constitutes second filter means of a receiver having a multirate transmission function according to a fourth embodiment of the present invention.

FIG. 18 is an explanatory diagram showing frequency allocation of the receiver according to the fourth embodiment.

FIG. 19 is a block diagram showing the configuration of a receiver having a multirate transmission function according to a fifth embodiment of the present invention.

FIG. 20 is an explanatory diagram showing the output of the baseband filter of the receiver of the fifth embodiment.

FIG. 21 is a block diagram showing the configuration of a conventional receiver having a multirate transmission function.

FIG. 22 is an explanatory diagram showing an example of frequency allocation in a conventional receiver.

FIG. 23 is an explanatory diagram showing respective frequency characteristics of (a) a first IF filter, (b) a second IF filter, and (c) a third IF filter in the first filter means of the conventional receiver. .

FIG. 24 is an explanatory diagram showing characteristics of the second filter means in the case of receiving (a) a signal having a bandwidth of 20 MHz and (b) a signal having a bandwidth of 5 MHz in the conventional receiver.

[Explanation of symbols]

2 Frequency conversion means 3 synthesizer 4 First filter means 40 Intermediate Frequency (IF) Filter 6 Quadrature demodulation means 7 Second filter means 7a First baseband filter 7b Second baseband filter 70 baseband filter 8 A / D conversion means 10 System band switching signal generation means 11 Synthesizer 12 90 degree phase shifter 13 Loopback removal filter 14 Switched Capacitor Filter (SCF)

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-8-340268 (JP, A) JP-A-10-209904 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 1/10 H03H 19/00

Claims (7)

(57) [Claims] 1. A frequency conversion means for converting a received high frequency signal into an intermediate frequency, a first filter means connected to an output end of the frequency conversion means, and an output end of the first filter means. and quadrature demodulating means being, comprising a second filter means connected to an output terminal of the quadrature demodulating unit, and the second connected to the a / D converting means to an output end of the filter means is used Minimum bandwidth with multiple bandwidths
In a receiver having a multi-rate transmission function used in a wireless communication system that performs communication using a bandwidth and a plurality of signal bandwidths that are integral multiples thereof , the first filter means includes the frequency conversion means. of the plurality of signal bandwidth supplied through the widest
Receiver having a multi-rate transmission function, characterized in that it comprises a single bandpass filter having a bandwidth corresponding to the sum of the narrowest signal bandwidth and signal bandwidth. 2. The second filter means is the widest
When performing communication using a signal bandwidth, the first signal bandwidth wider signal bandwidth than the filter means, and the cut-off frequency with the highest signal bandwidth
The function as a low-pass filter, when performing communication using the narrow signal bandwidth <br/> the signal band to perform communication
The receiver having a multi-rate transmission function according to claim 1, which functions as a bandpass filter having a width . 3. A synthesizer for generating a local signal of a predetermined frequency and supplying the local signal to the frequency converting means,
The interval of the predetermined frequency of the local signal generated by the synthesizer is 2 times the narrowest signal bandwidth.
The receiver having a multi-rate transmission function according to claim 1, wherein the receiver is doubled . 4. A frequency conversion means for converting a received high frequency signal into an intermediate frequency, a first filter means connected to an output end of the frequency conversion means, and an output end of the first filter means. and quadrature demodulating means being, comprising a second filter means connected to an output terminal of the quadrature demodulating unit, and the second connected to the a / D converting means to an output end of the filter means is used Minimum bandwidth with multiple bandwidths
In a receiver having a multi-rate transmission function used in a wireless communication system that performs communication using a bandwidth and a plurality of signal bandwidths that are integral multiples thereof , the first filter means includes the frequency conversion means. of the plurality of signal bandwidth supplied through the most the maximum transmission bandwidth of the bandwidth of wide signal which has as its pass band width, the carrier frequency of the widest signal bandwidth, the first A receiver having a multi-rate transmission function, comprising one band-pass filter controlled to have a center frequency of a pass band width of the filter means. 5. When the communication is performed using the maximum transmission signal bandwidth , the second filter means has a bandwidth of 2
Acts as a low pass filter having a set cut-off frequency so that the frequency of the first band, the minimum transmission
5. When the communication is performed using a signal bandwidth , the second filter means functions as a bandpass filter that passes the bandwidth, and the reception having the multi-transmission rate according to claim 4. Machine. 6. The low-pass filter according to claim 1, wherein the second filter means comprises a low-pass filter whose cutoff frequency is selected according to a bandwidth used in communication. Receiver with multi-rate transmission function. 7. The second filter means includes a switched capacitor filter, and a cutoff frequency of the low pass filter is determined by a cutoff frequency of the switched capacitor filter. A receiver having the described multi-rate transmission function.