JP4189134B2 - Diversity receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is provided with a plurality of receiving antennas, and among these antennas, a switchable space diversity (= space diversity: SD) reception that is used by switching and selecting one that satisfactorily receives radio waves transmitted from a transmitter. In particular, the present invention relates to an antenna diversity type receiver in which only one receiving unit that performs demodulation processing or the like for each antenna is used and an antenna connected to the input side of the receiving unit is switched and selected.
[0002]
[Prior art]
The antenna diversity receiver includes a receiver for each antenna, and has a single receiver compared to an audio diversity receiver that switches and selects a signal that has been demodulated by each receiver. As a result, there is an advantage that the entire device can be reduced in size and cost. Accordingly, many antenna diversity receivers are used in various wireless communication systems such as a wireless microphone system. A schematic configuration of the antenna diversity receiver is shown in FIG.
[0003]
As shown in the figure, this receiver has a plurality of, for example, two receiving antennas 1 and 1 of A system and B system. These antennas 1 and 1 are each connected to the input side of the antenna switching circuit 2. The antenna switching circuit 2 switches and selects one of the antennas 1 and 1 in accordance with an antenna switching control signal to be described later and connects it to the input side of the high frequency unit 3 to make it so-called effective. This figure shows a state in which the antenna 1 of the A system is made effective by the antenna switching circuit 2. A high frequency (RF) reception signal obtained by receiving radio waves transmitted from a transmitter (not shown) by the effective antenna 1 is input to the high frequency unit 3 via the antenna switching circuit 2, Here, for example, after being amplified and converted into an intermediate frequency signal, it is input to the detector 4. The detection unit 4 detects the intermediate frequency signal, reproduces the original signal, for example, a low-frequency audio signal when the receiver is for a wireless microphone system, and outputs it from the output terminal 5. . The audio signal output from the output terminal 5 is input to a speaker (not shown).
[0004]
The antenna switching circuit 2 is controlled by the control unit 6. The control unit 6 has, for example, a CPU (central processing unit) configuration, and based on the level of the intermediate frequency signal input to the detection unit 4, the received electric field intensity of the radio wave by the antenna 1 that is currently enabled. Monitor E. Then, the control unit 6 compares the received electric field strength (strictly speaking, the signal level of the intermediate frequency signal) E obtained by the monitoring with a predetermined antenna switching level Ea, so that the received electric field strength E is the antenna switching level. When Ea or less, the switching control signal is generated and supplied to the antenna switching circuit 2 so that the antenna 1 different from the currently effective antenna 1 is enabled. The antenna switching level Ea referred to here is, for example, whether the currently effective antenna 1 receives a radio wave transmitted from a transmitter with relatively good sensitivity. This is a level that serves as a reference (so-called threshold value) for judging from the intensity E. In this way, by alternately switching the antennas 1 and 1 so as to maintain a certain or higher communication quality, the influence of, for example, dead points and fading can be avoided.
[0005]
[Problems to be solved by the invention]
However, in the antenna diversity system receiver as described above, when the antenna 1 that is effective by the antenna switching circuit 2 is switched, even though it is instantaneous, none of the antennas 1 and 1 are enabled. As a result, for example, as exaggeratedly shown in FIG. 4, the output signal of the antenna switching circuit 2 is lost for a moment and becomes discontinuous. It becomes. The discontinuous portion N of this signal appears as noise (the figure shows a situation when switching from the A-system antenna 1 to the B-system antenna 1 becomes effective). Therefore, every time the antenna switching circuit 2 is switched, the noise N is output, and there is a problem that the user feels very uncomfortable in hearing.
[0006]
Accordingly, an object of the present invention is to provide a diversity receiver that can suppress the generation of noise N during antenna switching as described above.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention includes a plurality of antennas that receive radio waves transmitted from a transmitter,
A first switching unit that switches and selects the effective antenna according to the first switching control signal so as to enable any of these antennas;
The reception signal output from the antenna that is enabled by the first switching unit is input, the reception signal is subjected to predetermined processing, for example, amplification processing or detection processing, and the processed signal is output to the output terminal. A receiver that outputs from
When the received electric field strength of the radio wave by the effective antenna is monitored and the received electric field strength falls below a predetermined reference level, an antenna different from the currently effective antenna is enabled. A first switching control unit that generates a first switching control signal and supplies the first switching control signal to the first switching unit;
Deterioration of the received signal to the receiving unit, for example, loss, or drop of the output signal of the receiving unit due to the decrease of the received signal, for example, missing Interpolation means for interpolation;
It comprises.
[0012]
The interpolating means includes a first time constant circuit having a first time constant, a second time constant circuit having a second time constant smaller than the first time constant, and a second switching control. In accordance with the signal, the output signal of the receiver is directly output from the output terminal, and the output signal of the receiver is output to the output terminal via the first or second time constant circuit. A second switching unit that switches to any one of the two states, and when the first switching unit enables any of the plurality of antennas, the second switching unit is In the first state, when the first switching unit switches an effective antenna among the plurality of antennas, the second switching unit is set to the second state only for a predetermined period. 2 switching control signals are generated and the second A second switching control unit for supplying the replacement unit includes. The second switching control unit first enables the first time constant circuit for the predetermined period, subsequently enables the second time constant circuit, and finally enables the first time constant circuit. In order to enable, the second switching control signal is generated and supplied to the second switching unit.
[0015]
As described above, when the output signal of the receiving unit is smoothed by the time constant circuit, the discontinuous portion of the output signal of the receiving unit is more smoothly interpolated by sequentially changing the magnitude of the time constant of the time constant circuit. be able to.
The time constant circuit can be constituted by, for example, a low-pass filter circuit having an attenuation band in a frequency band higher than a predetermined frequency. The cut-off frequency (predetermined frequency) of the low-pass filter circuit is relatively high in the audible frequency band, for example, when the diversity receiver of the present invention is for a wireless microphone system. It is desirable to set the frequency (about 1 kHz to 10 kHz). This is because the noise generated by the discontinuity of the output signal of the receiving unit is a signal having a relatively high frequency, and therefore, to eliminate the noise having a high frequency efficiently and inconspicuously. This is because it is effective to set the cut-off frequency to a relatively high frequency within the audible frequency band.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of the present embodiment. As shown in the figure, the receiver according to the present embodiment is provided with a changeover switch circuit 7 on the output side of the detector 4 in the receiver for the conventional wireless microphone system shown in FIG. Two low pass filter circuits 8 and 9 are provided. The changeover switch circuit 7 performs a switching operation in accordance with a switch control signal supplied from the control unit 6. The low-pass filter circuit 8 has a cutoff frequency fa of fa = 10 [kHz], and the low-pass filter circuit 9 has a cutoff frequency fb of fb = 1 [kHz]. is there. Since other configurations are the same as those in FIG. 4 described above, the same reference numerals are given to these equivalent parts, and detailed descriptions thereof are omitted.
[0017]
That is, the changeover switch circuit 7 outputs the detection output of the detection unit 4 directly from the output terminal 5 and outputs the detection output of the detection unit 4 via the low-pass filter circuit 8 in accordance with the squelch switching control signal. The state is switched between a state of outputting from the terminal 5 and a state of outputting the detection output of the detection unit 4 from the output terminal 5 via the low-pass filter circuit 9. When the control unit 6 switches the effective antenna 1 by the antenna switching circuit 2, at the same time, the detection unit 4 outputs the detection output of the low-pass filter filter circuit 8 → low-pass filter filter circuit 9 → low The switch / switch circuit 7 is controlled so as to be sequentially switched in the order of the pass / filter / filter circuit 8 and finally supplied directly to the output terminal 5 (strictly speaking, a switch switching control signal for realizing this control is provided). Generated and supplied to the changeover switch circuit 7). The series of switching operations of the selector switch circuit 7 is completed within a time slightly longer than the time required for switching the antenna 1 that is effective by the antenna switching circuit 2.
[0018]
Thus, when the antenna 1 to be enabled is switched by the antenna switching circuit 2, the detection output of the detection unit 4 is supplied to the output terminal 5 via the low-pass filter circuit 8 or 9, so that the antenna switching is performed. The discontinuous portion of the detection output that occurs can be smoothed. As a result, as shown by the dotted line S in FIG. 2, an effect equivalent to linear interpolation of the discontinuous portion N of the detection output can be obtained, and the discontinuous portion N is prevented from appearing as noise. it can.
[0019]
In the figure, a period a is a period during which the low pass filter circuit 8 is enabled, and a period b is a period during which the low pass filter circuit 9 is enabled. The lengths of these periods a and b are appropriately determined according to the characteristics of the discontinuous portion N, the switching operation characteristics of the antenna switching circuit 2 and the switching switch circuit 7, and the like.
[0020]
Further, the switching order of the low-pass filter circuits 8 and 9 by the selector switch circuit 7 is not limited to the order described in the present embodiment. The switching order may be determined as appropriate according to the characteristics of the discontinuous portion N, the switching operation characteristics of the antenna switching circuit 2 and the switching circuit 7, and the like.
[0021]
Further, although the cutoff frequencies fa and fb of the low-pass filter circuits 8 and 9 are set to fa = 10 [kHz] and fb = 1 [kHz], respectively, this is not restrictive. However, since the noise caused by the discontinuous portion N is a signal having a relatively high frequency, considering that the noise N having such a high frequency is efficiently and inconspicuously removed, The cut-off frequencies fa and fb of the pass filter circuits 8 and 9 are desirably set to relatively high frequencies in the audible frequency band, respectively, as in the present embodiment.
[0022]
In this embodiment, the two low pass filter circuits 8 and 9 are provided, but only one low pass filter circuit may be provided. However, the discontinuous portion N can be smoothly interpolated by providing a plurality of low-pass filter circuits 8 and 9 as in the present embodiment. In this way, the number of low-pass filter circuits 8 and 9 is better in terms of smooth interpolation. However, if the number is too large, the entire receiver becomes complicated and expensive, so this point The number of low-pass filter circuits is determined in consideration of the above.
[0023]
Further, although the changeover switch circuit 7 is provided between the output side of the detection unit 4 and the input side of the low-pass filter circuits 8 and 9, the present invention is not limited to this. For example, by providing the changeover switch circuit 7 between the output side of each of the low pass filter circuits 8 and 9 and the output terminal 5, the same operation and effect as the present embodiment may be achieved. .
[0024]
The changeover switch circuit 7 and the low-pass filter circuits 8 and 9 are provided on the output side of the detection unit 4. However, the present invention is not limited to this. For example, the same switch circuit and filter circuit are provided on the input side of the detection unit 4, and the output signal of the high-frequency unit 3 is input to the detection unit 4 directly or via the filter circuit. The same difference and effect may be achieved.
[0025]
In the present embodiment, the case where the present invention is applied to a diversity receiver for a wireless microphone system has been described, but it goes without saying that the present invention can also be applied to other wireless systems.
[0026]
The antenna switching circuit 2 according to the present embodiment corresponds to the first switching unit described in the claims, and the portion including the high frequency unit 3 and the detection unit 4 is the receiving unit described in the claims. Corresponding to The changeover switch circuit 7 corresponds to the second switching unit described in the claims, and the control unit 6 corresponds to each of the first and second switching control units described in the claims. The control unit 6 can also be configured by a pure hardware circuit, for example. Each low-pass filter circuit 8 and 9 corresponds to the time constant circuit recited in the claims. In place of these low pass filter circuits 8 and 9, other circuits such as a band pass filter circuit may be used. The present embodiment has been described on the assumption that the output of the antenna switching circuit 2 is interrupted and missing when the antenna switching circuit 2 switches from one antenna 1 to the other antenna 1. However, the antenna switching circuit 2 may be configured with a switching circuit using a diode. In this case, the antenna output before switching and the antenna output after switching may be combined and output. If the antenna output after switching is different in phase from the antenna output before switching, the synthesized antenna output is not lost, but the level is lowered and may be lower than the reception sensitivity. Even in such a case, the present invention is effective.
[0027]
【The invention's effect】
As described above, according to the present invention, a decrease in the reception signal to the reception unit due to the state where none of the antennas is enabled at the time of antenna switching, or the output signal of the reception unit due to the decrease in the reception signal The decrease is interpolated by the interpolation means. Therefore, it is possible to suppress the occurrence of noise due to the decrease in the signal and to realize comfortable wireless communication.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention.
FIG. 2 is a diagram showing a reception operation in the embodiment.
FIG. 3 is a block diagram showing a schematic configuration of a conventional diversity receiver.
FIG. 4 is a diagram illustrating a reception operation of a conventional diversity receiver.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reception antenna 2 Antenna switching circuit 3 High frequency part 4 Detection part 5 Output terminal 6 Control part 7 Changeover switch circuit 8, 9 Low pass filter circuit

Claims (2)

Multiple antennas that receive radio waves sent from the transmitter,
A first switching unit that switches and selects the effective antenna according to the first switching control signal in a state in which any one of these antennas is enabled;
A reception unit that receives a reception signal output from an antenna that is enabled by the first switching unit, performs a predetermined process on the reception signal, and outputs the reception signal from an output terminal;
When the received electric field strength of the radio wave by the effective antenna is monitored and the received electric field strength falls below a predetermined reference level, an antenna different from the currently effective antenna is enabled. A first switching control unit that generates the first switching control signal in a state and supplies the first switching control signal to the first switching unit;
Interpolating means for interpolating a decrease in the received signal to the receiving unit that occurs at the moment of switching the antenna that is effective by the first switching unit, or a decrease in the output signal of the receiving unit due to the decrease in the received signal. Equipped,
The interpolation means is
A first time constant circuit having a first time constant;
A second time constant circuit having a second time constant smaller than the first time constant;
In accordance with a second switching control signal, the output of the receiver is output via the first state in which the output signal of the receiver is directly output from the output terminal and the first or second time constant circuit. A second switching unit that switches to any one of a second state in which a signal is output from the output terminal;
When the first switching unit enables any of the plurality of antennas, the second switching unit is set to the first state, and the first switching unit is enabled among the plurality of antennas. When switching antennas, the second switching control signal is generated and supplied to the second switching unit so that the second switching unit is in the second state for a predetermined period. The control unit,
The second switching control unit first enables the first time constant circuit for the predetermined period, subsequently enables the second time constant circuit, and finally enables the first time constant circuit. A diversity receiver configured to generate the second switching control signal and supply the second switching control signal to the second switching unit so as to enable the circuit . 2. The diversity receiver according to claim 1, wherein the first time constant circuit includes a filter circuit having an attenuation band in a first frequency band, and the second time constant circuit includes the first frequency band. A diversity receiver configured by a filter having an attenuation band in a lower second frequency band .

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