JP3743059B2 - Direct conversion receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio communication apparatus such as a selective call receiver, a cordless remote controller, and a cordless telephone, and more particularly to a receiver using a direct conversion reception system, that is, a homodyne system as a reception demodulation system.
[0002]
[Prior art]
Direct conversion receivers have many advantages over heterodyne systems. In the heterodyne method, a filter for removing image components is necessary to process a received high-frequency signal after converting it to an intermediate frequency. As this filter, a ceramic filter or a crystal filter is usually used, but these filters are expensive and have a large shape. The direct conversion receiver directly converts the received high-frequency signal into a low-frequency signal near the baseband, so that no image component is generated. Therefore, the above filter is unnecessary. In general, a filter that removes adjacent channel components is required. However, since a signal to be processed has a low frequency, an active filter having a low-pass characteristic can be used, and an IC can be easily formed. That is, since an expensive and large filter is unnecessary, the direct conversion receiver can be realized at a low cost and a small size.
[0003]
FIG. 7 is a block diagram showing a configuration of a conventional direct conversion receiver. In FIG. 7, 1 is an RF signal input terminal, 2 is a local signal input terminal, 11 is a demodulator, 12 is a data output terminal, 71 is a phase shift distributor, 201 is a distributor, 202 is a first mixer, and 203 is The second mixer, 204 is the first output of distributor 201, 205 is the second output of distributor 201, 206 is the first local signal, 207 is the second local signal, and 208 is the first mixer. IF signal 209 is the IF signal of the second mixer. The RF signal input to the RF input terminal 1 is divided into two by the distributor 201. The local signal input to the local signal input terminal 2 is distributed by the phase shift distributor 71 into a first local signal 206 and a second local signal 207 having a phase difference of 90 degrees. The first output 204 of the distributor 201 and the first local signal 206 are input to the first mixer 202, and the second output 205 of the distributor 201 and the second local signal 207 are input to the second mixer 203. Is done. Here, the frequency of the local signal is set to be the same as the center frequency of the RF signal, so that the RF signal is frequency-converted by the mixers 202 and 203 to the first IF signal 208 and the second IF signal 209 having the baseband frequency, respectively. Is done. The two IF signals are input to the demodulator 11. The demodulator 11 performs demodulation after applying a band limiting filter for channel selection, and outputs demodulated data from the data output terminal 12. The above is the basic operation of the direct conversion receiver.
[0004]
[Problems to be solved by the invention]
However, the direct conversion receiver has a weak point against interference because the frequency of the IF signal is the baseband frequency as described above. That is, the baseband frequency is set in the range of about 0 Hz to several tens of kHz. Here, when the input RF signal is subjected to amplitude modulation, due to the distortion characteristics of the mixer, a signal component of the amplitude modulation frequency or twice the frequency is generated during frequency conversion to the IF signal. Is included in the IF signal. The amplitude modulation frequency is generally about several kHz, and this modulation frequency component and the IF signal of the baseband frequency are present in substantially the same frequency band, which causes reception interference. Amplitude modulation of an RF signal may be subject to large amplitude fluctuations due to fading in spatial propagation even when it is not subjected to amplitude modulation during transmission. Further, even when an RF signal other than the desired wave is input to the mixer and this signal is subjected to amplitude fluctuation, the same interference is caused. Furthermore, when a plurality of RF signals are simultaneously input to the mixer, interference may occur even if the signal is not subjected to amplitude modulation.
[0005]
SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object of the present invention is to provide a direct conversion receiver that can suppress reception interference due to an amplitude modulation component of an RF signal input to a mixer and obtain stable reception characteristics.
[0006]
[Means for Solving the Problems]
In order to solve this object, the present invention has a configuration in which local signals having a phase difference of 180 degrees are input to two mixers, and the difference between the IF output signals is obtained.
[0007]
According to the above invention, the amplitude modulation frequency component generated in each mixer is canceled by taking the difference between the IF signals. At this time, the necessary amplitude signal component (the frequency of the difference between the RF signal and the local signal) is not canceled, and the amplitude modulation frequency component is canceled.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
A distributor that divides the RF signal into four, a first mixer that inputs a first output of the distributor and a first local signal, a second output of the distributor and a second local signal that are input A second mixer; a third mixer for inputting a third output of the distributor and a third local signal; and a fourth mixer for inputting a fourth output of the distributor and a fourth local signal. A first subtractor that outputs a voltage difference between the IF signal of the first mixer and the IF signal of the second mixer, the IF signal of the third mixer, and the IF signal of the fourth mixer A second subtractor that outputs a voltage difference between the first subtractor and a demodulator that receives the output of the first subtractor and the output of the second subtractor, and the second, third, and fourth local The phase of the signal is 180 degrees and 90 degrees with respect to the phase of the first local signal, respectively. One in which a structure is a spare 270 degrees.
[0009]
Embodiments of the present invention will be described below with reference to the drawings.
Example 1
FIG. 1 is a block diagram showing a direct conversion receiver according to a first embodiment of the present invention. In FIG. 1, 1 is an RF signal input terminal, 2 is a local signal input terminal, 3 is a distributor, 4 is a phase shift distributor, 5 is a first mixer, 6 is a second mixer, and 7 is a third mixer. , 8 is a fourth mixer, 9 is a first subtractor, 10 is a second subtractor, 11 is a demodulator, 12 is a data output terminal, 13 is a first output of the distributor 3, and 14 is a distributor. 3 is the second output of distributor 3, 15 is the third output of distributor 3, 16 is the fourth output of distributor 3, 17 is the first local signal, 18 is the second local signal, and 19 is the third output. Local signal, 20 is the fourth local signal, 21 is the first IF signal, 22 is the second IF signal, 23 is the third IF signal, 24 is the fourth IF signal, and 25 is the output of the subtractor 9 , 26 are the outputs of the subtractor 10.
[0010]
First, the operation of the direct conversion receiver of this embodiment will be described. The RF signal input to the RF input terminal 1 is divided into four by the distributor 3 to the first, second, third and fourth outputs 13, 14, 15 and 16. The local signal input to the local signal input terminal 2 is divided into four by the phase shift distributor 4 into the first, second, third and fourth local signals 17, 18, 19 and 20. Here, the phases of the second, third, and fourth local signals have a phase difference of 180 degrees, 90 degrees, and 270 degrees, respectively, with respect to the phase of the first local signal. The first output 13 of the distributor 3 and the first local signal 17 are input to the first mixer 5, and the second output 14 of the distributor 3 and the second local signal 18 are input to the second mixer 6. The third output 15 of the distributor 3 and the third local signal 19 are input to the third mixer 7, and the fourth output 16 of the distributor 3 and the fourth local signal 20 are input to the fourth mixer 8. Is input. Here, the frequency of the local signal is set to be the same as the center frequency of the RF signal. Therefore, the RF signal is frequency-converted into an IF signal having a baseband frequency by a mixer. The first IF signal 21 and the second IF signal 22 are input to the first subtractor 9, and the third IF signal 23 and the fourth IF signal 24 are input to the second subtractor 10.
[0011]
The subtractors 9 and 10 output outputs 25 and 26 as the difference between the voltages of the two IF signals, respectively. Subtractor outputs 25 and 26 are input to demodulator 11. Demodulation is performed by the demodulator 11, and demodulated data is output from the data output terminal 12.
[0012]
Next, the reason why the interference due to the amplitude modulation frequency component of the RF signal can be suppressed will be described. When attention is paid to the first mixer 5 and the second mixer 6, the phases of the RF signals inputted to both mixers are the same, and the two local signals, that is, the first local signal 17 and the second local signal 18 are the same. The phase is 180 degrees. At this time, a necessary IF signal component (frequency component of the difference between the RF signal and the local signal) among the signal components of the IF signals 21 and 22 output from both mixers has a phase difference of 180 degrees. However, the phases of the amplitude modulation frequency components generated in the baseband are the same in both. Therefore, when the difference between the voltages of the two IF signals is calculated by the subtractor 9, the amplitude modulation frequency component is canceled. At this time, the necessary IF component (frequency component of the difference between the RF signal and the local signal) is added and is not canceled.
[0013]
The third mixer 7 and the fourth mixer 8 are also operated in the same manner as described above. That is, the amplitude modulation frequency component is canceled by taking the difference in amplitude between the third IF signal 24 and the fourth IF signal 25 by the subtractor 10.
[0014]
The phase shift distributor used in the present embodiment can be realized by the configuration shown in FIG. 5, for example. In FIG. 5, 101 is a 90-degree phase shift distributor, and 102 is a balun transformer. With this configuration, the input signal can be distributed into four signals having phases of 0 degrees, 180 degrees, 90 degrees, and 270 degrees, respectively.
[0015]
(Example 2)
2 is a block diagram showing a direct conversion receiver according to a second embodiment of the present invention. In FIG. 2, 31 is a phase shift distributor, 32 is a phase shift distributor, 33 is a first output of the phase shift distributor 31, 34 is a second output of the phase shift distributor 31, and 35 is a first local. Signal 36 is a second local signal. The same constituent elements as those in the first embodiment are denoted by the same numbers.
[0016]
The difference between the present embodiment and the first embodiment is in the method of inputting the RF signal and the local signal. In this embodiment, the RF signal input to the RF signal input terminal 1 is distributed by the phase shift distributor 31 to two outputs 33 and 34 having a phase difference of 90 degrees. On the other hand, the input to the local signal input terminal 2 is distributed by the phase shift distributor 32 into a first local signal 35 and a second local signal 36 having a phase difference of 180 degrees. The first output of the phase shift distributor 31 is input to the first mixer 5 and the second mixer 6, and the second output of the phase shift distributor 31 is input to the third mixer 7 and the fourth mixer 8. Is done. The first local signal 35 is input to the first mixer 5 and the third mixer 7, and the second local signal 36 is input to the second mixer 6 and the fourth mixer 8.
[0017]
Here again, the phase relationship between each RF signal and IF signal input to the first mixer 5 and the second mixer 6 is found to be the same as in the first embodiment. As a result, the amplitude modulation frequency component can be canceled. Since the third mixer 7 and the fourth mixer 8 operate in the same manner, the amplitude modulation frequency component is canceled.
[0018]
The advantage of the configuration of this embodiment is that it can be configured with a two-output phase shift distributor. That is, the phase shift distributor 31 is a two-signal output with a phase difference of 90 degrees, and the phase shift distributor 32 is a two-signal output with a phase difference of 180 degrees. In the case of the first embodiment, a four-output phase distributor is necessary, but this embodiment has an advantage that it can be configured by such a simple distributor. Further, the phase shift and distribution functions can be divided into two distributors, so that the phase and amplitude accuracy can be improved.
[0019]
In the present embodiment, the phase shift distributor 31 on the RF signal side may be configured to output 180 degrees in phase difference, and the phase shift distributor 32 on the local signal side may be configured to output 90 degrees in phase difference. In this case, the first output of the phase shift distributor 31 is input to the first mixer 5 and the third mixer 7, and the second output of the phase shift distributor 31 is the second mixer 6 and the fourth mixer. 8 is input. The first local signal 35 is input to the first mixer 5 and the second mixer 6, and the second local signal 36 is input to the third mixer 7 and the fourth mixer 8. Similar effects can be obtained.
[0020]
Example 3
FIG. 3 is a block diagram showing a direct conversion receiver according to a third embodiment of the present invention. In FIG. Local signal input terminal 42 is connected to 2nd. Local signal input terminal, 43 is a first mixer, 44 is a second mixer, 45 is a third mixer, 46 is a fourth mixer, 47 is a fifth mixer, 48 is a first output of the distributor 3 , 49 is the second output of the distributor 3, 50 is the third output of the distributor 3, 51 is the fourth output of the distributor 3, 52 is the first local signal, 53 is the second local signal, 54 is a third local signal, 55 is a fourth local signal, 56 is a first 2nd. IF signal 57 is the second 2nd. IF signal 58 is a third 2nd. IF signal 59 is the fourth 2nd. IF signal, 60 is 1st. IF signal. The same constituent elements as those in the first embodiment are denoted by the same numbers.
[0021]
A major difference between the present embodiment and the first and second embodiments is that a first mixer 43 is added. In the present embodiment, the RF signal input to the RF signal input terminal 1 is sent to the 1st. The signal is mixed with the local signal input to the local signal input terminal 41. Here, the frequency of the local signal is set to a frequency higher or lower than that of the RF signal. 1st. Output from the first mixer 43. The IF signal 60 includes a frequency component of the difference between the frequency of the RF signal and the IF signal. As a result, the frequency of the desired signal is converted to a lower frequency. The subsequent processing is almost the same as in the first embodiment. That is, 1st. The IF signal 60 is divided into four by the distributor 3, and the outputs 48, 49, 50 and 51 of the distributor are input to the second, third, fourth and fifth mixers 44, 45, 46 and 47, respectively. On the other hand, 2nd. The local signal input to the local signal input terminal 42 is divided into four signals having different phases by the phase shift distributor 4, that is, the first, second, third and fourth 2nd. Distributed to local signals 52, 53, 54, 55. These are input to the second, third, fourth, and fifth mixers 44, 45, 46, and 47, respectively. Here, the second, third and fourth 2nd. The phase of the local signal is set to 180 degrees, 90 degrees, and 270 degrees with respect to the phase of the first local signal, respectively. The first and second 2nd. The difference between the voltages of the IF signals 56 and 57 is output from the first subtracter 9, and the third and fourth 2nd. The voltage difference between the IF signals 58 and 59 is output from the second subtractor 9, and the outputs 26 and 27 of the first and second subtractors are input to the demodulator 11.
[0022]
This embodiment is characterized in that the frequency of the desired signal is lowered by performing frequency conversion in advance by the first mixer as described above. In the present embodiment, the maximum effect can be obtained when the distortion characteristics generated in each mixer are the same. However, since the frequency of the RF signal is a high frequency band such as several GHz or several hundred MHz, the distortion characteristics of the mixers vary. Further, the phase difference and the amplitude of each output of the phase shift distributor must be set accurately, but the error becomes large at the above high frequency. In this case, sufficient amplitude modulation frequency components cannot be canceled. However, at a relatively low frequency such as several MHz or several hundred kHz, it is easy to align the characteristics of the mixer, and it is relatively easy to set the phase shift distributor accurately. Therefore, as in the present embodiment, the amount of cancellation of the amplitude modulation frequency component that becomes an interference can be increased by directly converting the desired wave to a low frequency and then performing the direct conversion.
[0023]
(Example 4)
FIG. 4 is a block diagram showing a direct conversion receiver according to a fourth embodiment of the present invention. 4, 71 is a phase shift distributor, 72 is a first mixer, 73 is a first 1st. IF signal 74 is the second 1st. The IF signal, 75 is a first local signal, and 76 is a second local signal. Moreover, the same number is described about the same component as Example 1 and 3. FIG.
[0024]
The difference between the present embodiment and the third embodiment is that the first mixer 72 outputs a balanced IF signal. For this reason, 2nd. The local signal phase shift distributor 71 can have a two-distribution configuration with a phase difference of 90 degrees. However, the first 1st. The IF signal 73 is sent to the second and fourth mixers 44 and 46, and the second 1st. The IF signal 74 is input to the third and fifth mixers 45 and 47, the first local signal 75 is input to the second and third mixers 44 and 45, and the second local signal 76 is input to the fourth and fourth mixers 45 and 47. 5 mixers 46 and 47.
[0025]
In order to obtain a balanced IF signal output, for example, the circuit shown in FIG. 6 can be used. That is, an RF signal and a local signal are input to the base of the transistor, and two IF signals are output from the collector and the emitter, respectively. Here, a resistor R1 is inserted between the collector power supply and the collector, and a resistor R2 is inserted between the emitter and the ground. Then, by appropriately selecting the resistance values of R1 and R2, it is possible to obtain two IF signals having the same amplitude with the phases reversed. Thus, by using a mixer with a balanced output IF signal, a distributor is not necessary, and the phase shift distributor 75 may have only two outputs, so that the circuit scale can be greatly reduced.
[0026]
【The invention's effect】
As is clear from the above description, according to the direct conversion receiver of the present invention, the following effects can be obtained.
[0027]
By inputting local signals with a phase difference of 180 degrees into the two mixers and taking the difference between the IF output signals, the amplitude modulation frequency components generated in the baseband frequency band can be canceled by the two mixers.
[0029]
Also, by adding one more mixer, converting the frequency of the RF signal in advance, lowering the frequency of the desired signal and then directly converting and demodulating, it is easy to align the characteristics of the mixer. Since it can be configured accurately, the amount of cancellation of the amplitude modulation frequency component which becomes an obstacle can be increased.
[0030]
Further, the use of a mixer with a balanced output type IF signal eliminates the need for a distributor, and the phase shift distributor may have a two-output configuration, so that the circuit scale can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a direct conversion receiver according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a direct conversion receiver according to Embodiment 2 of the present invention. FIG. 4 is a block diagram showing a direct conversion receiver according to a fourth embodiment of the present invention. FIG. 5 is a circuit diagram of a phase shift five-way distributor of the receiver. Balanced IF signal output mixer circuit diagram [Fig. 7] Block diagram showing the configuration of a conventional direct conversion receiver [Explanation of symbols]
1 RF signal input terminal 2 Local signal input terminal 3, 31 Distributor 4, 32, 71 Phase shift distributor 5, 43, 72 Mixer 6, 44 Second mixer 7, 45 Third mixer 8, 46 Fourth Mixer 9 First subtractor 10 Second subtractor 11 Demodulator 12 Data output terminals 13, 48 First output 14 of distributor 3 49 Second output 15 of distributor 3 15 50 Second of distributor 3 3 output 16, 51 fourth output 17, 35, 52, 75 of distributor 3 first local signal 18, 36, 53, 76 second local signal 19, 54 third local signal 20, 55 4 local signals 21 1st IF signal 22 2nd IF signal 23 3rd IF signal 24 4th IF signal 25 output 26 of subtractor 9 output 33 of subtractor 10 first output 34 of distributor 31 Second output 41 of distributor 31 st. Local signal input terminal 42 2nd. Local signal input terminal 47 Fifth mixer 56 First 2nd. IF signal 57 second 2nd. IF signal 58 3rd 2nd. IF signal 59 4th 2nd. IF signal 60 1st. IF signal 73 First 1st. IF signal 74 Second 1st. IF signal

Claims (2)

  RF signal and 1st. A first mixer for inputting a local signal; a distributor for distributing the IF signal of the first mixer into four; a first output of the distributor; and a first 2nd. A second mixer for inputting a local signal; a second output of the distributor; and a second 2nd. A third mixer for inputting a local signal; a third output of the distributor; and a third 2nd. A fourth mixer for inputting a local signal; a fourth output of the distributor; and a fourth 2nd. A fifth mixer for inputting a local signal; a first subtractor for outputting a voltage difference between the IF signal of the second mixer and the IF signal of the third mixer; and the IF signal of the fourth mixer And a second subtractor that outputs the difference in voltage of the IF signal of the fifth mixer, and a demodulator that inputs the output of the first subtractor and the output of the second subtractor. 2, 3rd and 4th 2nd. A direct conversion receiver in which the phase of the local signal is 180 degrees, 90 degrees and 270 degrees with respect to the phase of the first local signal, respectively.   RF signal and 1st. The first and second 1st. A first mixer for outputting an IF signal; and the first 1st. IF signal and the first 2nd. A second mixer for inputting a local signal; and the second 1st. IF signal and the first 2nd. A third mixer for inputting a local signal; and the first 1st. IF signal and the second 2nd. A fourth mixer for inputting a local signal; and the second 1st. IF signal and the second 2nd. A fifth mixer for inputting a local signal; a first subtractor for outputting a voltage difference between the IF signal of the second mixer and the IF signal of the third mixer; and the IF signal of the fourth mixer And a second subtractor that outputs the difference in voltage of the IF signal of the fifth mixer, and a demodulator that inputs the output of the first subtractor and the output of the second subtractor. 2, 3rd and 4th 2nd. A direct conversion receiver in which the phase of the local signal is 180 degrees, 90 degrees and 270 degrees with respect to the phase of the first local signal, respectively.

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