JPS626372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a muting device in a radio receiver.

[Background of the invention]

FM radio broadcasts are widely enjoyed because of their high quality, and there is strong demand from viewers for more sources. In other words, the number of broadcast stations is expected to increase. However, as the number of broadcasting stations increases, the problem of interference, which was not a problem in the past, becomes an urgent problem. Among them, intermodulation interference generates an unpleasant "jerky" sound due to beats with the desired receiving frequency, so improvement is desired.

Intermodulation interference is a phenomenon in which two or more interfering radio waves generate a spectrum that looks like a broadcast radio wave at a frequency different from those of the interfering radio waves. This is due to the nonlinearity of the amplification element and mixing element in the receiver. arise. For example, suppose that the transfer characteristic of an amplifying element has nonlinearity as expressed by equation (1).

I=a ₀ +a ₁ v+a ₂ v ² +a ₃ v ³ +…… (1) However, I: Output current v: Input voltage In the above equation, if there are two input signals f ₁ and f ₂ , then I =a ₀ +a ₁ (v ₁ sinω ₁ t+v ₂ sinω ₂ t) +a ₂ (v ₁ sinω ₁ t+v ₂ sinω ₂ t) ² +a ₃ (v ₁ sinω ₁ t+v ₂ sinω ₂ t) ³ ...(2) However v ₁ and v ₂ become signal voltages of f ₁ and f ₂ ω ₁ ; 2πf ₁ , ω ₂ ; 2πf ₂ .

Expanding the fourth term in equation (2), that is, the cubed term, using the trigonometric formula: 3/4a ₃ v _{1 2} ^v ₂ sin2π(2f ₁ −f ₂ )t ......(3) 3/4a ₃ v ₁ v ₂ ² sin2π(2f ₂ −f ₁ )t (4) This includes the spectrum. In this case, if f ₂ = f ₁ + Δf, the spectra of equations (3) and (4) will be expressed as f ₁ −Δf, f ₁ +2Δ, as shown by the broken line in Figure 1.
It occurs at f. Therefore, if the reception frequency of the receiver is tuned to f ₁ −Δf or f ₁ +2Δf, if there is no broadcast radio wave (signal) there, f ₁ , f ₂
A mixture of broadcast contents will be received, and broadcast radio waves (signals) will be received at f ₁ - Δf or f ₁ + 2 Δf.
Sometimes these spurious signals caused by intermodulation become an interference in receiving the broadcast signal. Even if the false signal generated by intermodulation is not the same frequency as the desired reception frequency, if it is near the desired reception frequency, it will cause similar interference, so improvements are desired.

As a means to solve this problem, in the high frequency circuit shown in Fig. 2, elements with less nonlinearity are used for the high frequency amplifier circuit 3 and mixer circuit 6, and the selectivity of the frequency selection circuit 2 or 4 is increased. This is done to lower the level of interference waves input to the high-frequency amplifier circuit 3 and mixer circuit 6, but this increases insertion loss and reduces practical sensitivity, so intermodulation interference cannot be reduced to a satisfactory level. It is difficult to improve. In FIG. 2, 1 is an antenna and 5 is a local oscillator.

In addition to the above method, there is a method of controlling the input levels of the high frequency amplifier circuit 3 and mixer circuit 6 using AGC. Figure 3 shows AGC commonly performed in the past.
A block diagram of the circuit is shown. The signal converted to an intermediate frequency by the mixer circuit 6 is demodulated through an intermediate frequency filter 7, an amplifier 8, and an FM detector 9. In this case, the control signal for AGC is input from the amplifier 8 to the level detector 19, and is extracted by the level detector 19 as a DC voltage according to the input signal level, thereby controlling the gain of the high frequency amplifier circuit 3.

However, this method is of little use against the above-mentioned interference. This is because if _the reception frequency of the receiver is tuned to _{f 1} −Δf in FIG. This is because it is difficult to obtain a sufficient AGC voltage due to the interfering radio waves, which have frequencies Δf and 2Δf apart from the intermediate frequency and are attenuated by the intermediate frequency filter 7, causing interference. Since the band of the intermediate frequency filter 7 is determined so as not to be influenced by adjacent stations, the AGC voltage is hardly obtained by interfering radio waves, and is not useful for improving the interference caused by the above-mentioned intermodulation.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, improve intermodulation interference without impairing reception characteristics during weak input, and provide a muting method for a radio receiver that can provide good reception characteristics. We are in the process of providing equipment.

[Summary of the invention]

In order to achieve the above object, the present invention introduces a control device with a calculation function such as a microcomputer to control the reception frequency, searches for and calculates the presence and strength of broadcast radio waves that fall at the desired reception frequency,
According to the result, the control device performs intermodulation interference reduction control, and means is provided for preventing unnecessary audio from being output during the intermodulation interference reduction processing period.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings. FIG. 4 is a block diagram showing one embodiment of the present invention. In Fig. 4, 1 is an antenna, 2 is a frequency selection circuit, and 3 is a broadcast radio wave (reception frequency) induced by the antenna 1 and passed through the frequency selection circuit 2.
4 is a frequency selection circuit, 5 is a local oscillation circuit of the channel selection device, and 6 is a mixer of the output signal of the local oscillation circuit and the output signal that has passed through the frequency selection circuit 4 of the high-frequency amplification circuit 3. 7 is an intermediate frequency filter, 8 is an intermediate frequency amplifier circuit, and 9 is an FM detector, which constitute a well-known superheterodyne receiver. The local oscillation circuit 5, which is a tuning device, generates a stable reference frequency based on a crystal oscillator 51.
a reference signal generator 52 that oscillates fr, a voltage controlled oscillator (VCO) 53, and a programmable divider 54 that divides the oscillation frequency fe of the VCO to 1/N.
and the output frequency fe/of the programmable divider
A phase comparator 55 that compares the phase of N and the output frequency fr of the reference signal generator 52 to detect the phase difference and obtain a DC voltage according to the phase difference; and a phase comparator 55 that smoothes the output voltage of the phase comparator. , and a low frequency converter 56 which guides the signal to the VCO 53, and these are generally constructed from a well-known PLL circuit. Here, if the frequency fr of the reference signal generator 52 is set to fr=100 KHz, for example, by changing the frequency division ratio N of the programmable divider 54, reception becomes possible in steps of 100 KHz. Reference numeral 10 denotes a control device connected to the programmable divider 54 of the local oscillation circuit 5 to control its frequency division ratio N, and this device performs an arithmetic operation having a processing function as shown in FIG. 6 based on the program of the program section 120. Processing unit 110 and storage device 1
It has 30. 11 is its operation keyboard. 14 is an intermediate frequency amplifier 8 and an arithmetic processing unit 11
0 and detects when the reception level of the receiver reaches a certain level. Reference numeral 15 denotes an intermodulation interference reduction means, such as a gain control device, which is connected in the previous stage (high frequency stage) of the mixer circuit 6 of the receiver, for example, between the antenna 1 and the frequency selection circuit 2, and is used to reduce intermodulation interference output. In this device, the gain of the receiver is variably controlled by the output signal of the arithmetic processing section 110, and thereby,
The intermodulation interference is reduced.

The gain control device 15 includes a resistor 1 as shown in FIG.
There are a method of switching the output voltage divided by 51 and 152 by a switch 153 controlled by the control device 10, and a method of controlling the current of the light emitting element 155 using cadmium sulfide CdS 154 as shown in FIG. 5b. However, the present invention is not limited to these methods, and methods such as changing the tuning frequency of the frequency selection circuits 2 and 4 of the receiver, or controlling the bias and gain of the high frequency amplification circuit 3 may be used. It's okay. In other words, it goes without saying that anything that can reduce intermodulation interference is good. Reference numeral 16 denotes a display device connected to the output of the arithmetic processing unit 110 of the control device 10 and composed of a transistor 161, a resistor 162, and a display 163. This indicates that the interference reduction device according to the present invention is working. In the embodiment shown in FIG. 4, the gain control device 15 is driven by a control signal, but it can also be driven independently from the control device 10.

FIG. 6 shows an example of the processing flow of the control device 10 when a reception frequency designation is input to the control device 10 by the user.

The operation of the present invention will be explained below with reference to FIGS. 4 and 6. In FIG. 4, operate the desired operation key on the keyboard 11 to receive the desired reception frequency fs of the desired broadcast wave.
When the controller 10 specifies the arithmetic processing unit 11
0, the desired channel selection control signal _N0 corresponding to that frequency is calculated in the step of FIG. This value N ₀ is stored in the storage section 130c of the storage device 130 and is also input to the programmable divider 54. As a result, the local oscillation circuit 5 performs a PLL operation in a well-known manner, and the reception frequency of the receiver is set to fs. Next, the arithmetic processing unit 110 adds 1 to N ₀ in the step of FIG.
It is determined whether the value exceeds the value corresponding to the upper limit frequency of the reception band stored in 0a. Here, if N ₀ +1 is within the reception band, input this value into the programmable divider 54 in step and change the reception frequency by one step (for example,
100KHz) and level detector 14 at this frequency.
The presence or absence of the output is determined through the arithmetic processing unit 110, and the presence or absence of broadcasting is checked.

If there is no broadcast, return to step one more time.
Add and perform the same operation. If there is a broadcast in the step, this value is stored in the storage section 130d of the storage device 130, and the arithmetic processing section 110 calculates the currently received reception frequency (channel selection control signal N) and the desired reception frequency in the step of FIG. Difference frequency (ΔN=N- _N0 ) of frequency (desired station selection control signal _N0 )
(This is calculated from the value in the storage unit 130d in the storage unit 1
This is done by subtracting the value of 30c. ) step, the frequency at which the received frequency has a relationship that causes intermodulation (corresponding value N ₀ +2・Δ
N) is calculated. In the step, as in the step, it is determined whether this frequency is within the reception band. If it is outside the reception band, return to step. If it is within the receiving band in step, the process advances to step and determines whether or not there is a broadcast in the same manner as in step. If there is no broadcast, the process returns to the step to continue searching for frequency-related broadcasts that cause intermodulation interference.
If there is a broadcast in the step, it means that there is a broadcast with a frequency relationship that causes intermodulation interference. In this case, in the step, control is performed to lower the gain of the gain control device 15, and in the step, the value N ₀ is assigned to the programmable divider 54. input, complete the reception operation, and receive the desired reception frequency fs. If the reception band is exceeded in the step, it means that the search up to the upper limit frequency has been completed, and the process moves on to the step to return to the desired reception frequency and search toward the opposite side, that is, the lower limit frequency. The storage unit 130b of the storage device 130 stores the lower limit frequency of the reception band in advance. In FIG. 6, step ~ is the aforementioned step ~
This corresponds to , so the explanation will be omitted.

These series of operations are performed by the program unit 120 stored in advance. Also, the storage device 13
Other portions 130 of storage units 130a to 130d of 0
e... is used as a working area of the arithmetic processing section 110.

In order to simplify the explanation, in FIGS. 4 and 6, we have explained the case where the gain is controlled depending on the presence or absence of the output of the level detector 14, but in reality, interference becomes a problem when the interfering broadcast radio waves exceed a certain level. Since this is a case where the input radio wave is strong, it is actually desired that the level detector 14 is made sensitive only when the input radio wave is strong beyond a certain level.

Further, in the embodiment shown in FIG. 4, after searching for the presence or absence of interfering broadcast waves, the gain control device 15, which is an intermodulation interference reducing means, is controlled by the control device 10, and when there is no intermodulation interfering broadcast waves, a weak signal is detected. The effects of intermodulation interference can be improved in the presence of intermodulation interference broadcast radio waves without impairing the characteristics of Since the content is changed from moment to moment, the audio of the broadcast content is outputted in fragments to the output of the FM detector 9 at each location where the broadcast radio waves are present, resulting in a harshness to the ears.

FIG. 7 shows another embodiment of the present invention which corrects this problem, in which a plurality of level detectors 14 are used to control the gain control device 15 more precisely than in the case of FIG. This prevents unnecessary audio from being output while searching for the presence of intermodulation interfering broadcast waves.

In FIG. 7, 141, 142, and 143 indicate comparators, and the comparison reference level of each of the comparators is set by a comparison reference level source consisting of a power supply 148 and resistors 144-147. 17 is FM detector 8
It shows the muting circuit connected after the
During the intermodulation interference mitigation process shown in FIG. It is controlled by the control device 10 so as not to output audio.

In the embodiments of FIGS. 4 and 7 described above, it is assumed that, for example, the gain of the gain control device 15 is lowered by 5 dB. In this case, the input levels of high frequency amplifier circuit 3 and mixer circuit 6 are all lowered by 5 dB. The magnitude of intermodulation interference is proportional to v ₁ ² v ₂ or v ₁ v ₂ ² as shown in equations (3) and (4) above, and is reduced by lowering each of v ₁ and v ₂ by 5 dB. te v ₁ ² v ₂ or
v ₁ v ₂ ² is reduced by 15dB. In other words, by lowering the input level of the desired signal by only 5 dB, the magnitude of intermodulation interference can be lowered by 15 dB, significantly improving the interference.

In the embodiments shown in FIGS. 4 and 7, it takes time for channel selection to perform the processing shown in FIG. 5 every time a desired broadcast is received.

In order to correct this problem, for example, as shown in FIG.
8 is provided, and when the switch 18 is turned on, the control device 10 is operated as described above. In other words, the system may be configured so that the channel selection is performed according to the flow shown in FIG. 6, and when the switch 18 is turned off, the operation in the step of FIG. 6, that is, only the reception of the designated broadcast station, is performed. The problem of channel selection time can also be solved by a radio receiver having a memory preset function for broadcast stations. That is, in a radio receiver configured as shown in FIG. 4 or 5 and having a preset function, for example, when a desired receiving frequency is preset (stored in the channel preset storage device 130') as shown in FIG. In accordance with the flow shown in FIG. 6, it is determined whether or not intermodulation interference mitigation control is necessary, that is, whether gain control is necessary, and the information is stored in the storage device 130' together with the receiving frequency as shown in FIG. Correspond and remember. In other words, storage device 130'
The channel selection control value corresponding to the desired reception frequency is stored in the section, and the gain control value, which is the intermodulation interference reduction control value, is stored in the section, and a preset channel key (reading means) on the keyboard 11 is used to select a predetermined channel. When selected, the gain control value may be read out from the storage device 130' and supplied to the gain control device 15 without following the flow shown in FIG. In the case of Figure 8, the gain control
In this example, when ON and OFF are controlled, for example, when 2ch is selected, the frequency becomes 825MHz and the gain is reduced, and when 1ch is selected, the frequency becomes 800MHz, and no gain control is performed. Here, the storage device 130' is connected to the control device 1 as shown in FIGS. 9a and 9b.
0 is configured with a microcomputer, it does not matter whether it is configured inside or outside the microcomputer.

As described above, by providing the control device with a switch that cancels the flow action shown in FIG. 6 of the arithmetic processing section, or by providing the control device with a storage device that stores the contents as shown in FIG. 8, the time for selecting a channel can be shortened. It is possible to improve channel selection efficiency.

As can be seen from the above, according to the present invention, when there is no intermodulation interfering broadcast radio wave, the weak signal characteristics are not impaired, and when there is intermodulation interfering broadcast radio wave, the characteristics of the weak signal are not deteriorated. Intermodulation interference can be improved without the inconvenience caused by the IF filter in AGC, and unnecessary audio is prevented from being output during the intermodulation interference reduction processing period.
Good reception conditions can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a frequency spectrum diagram for explaining intermodulation interference, Fig. 2 is a block diagram showing the high frequency section of a radio receiver, Fig. 3 is a block diagram showing the configuration of a conventional AGC circuit, and Fig. 4 is a block diagram showing the configuration of a conventional AGC circuit. A block diagram of the interference mitigation device according to the present invention, FIG. 5 is a program diagram showing an overview of the processing flow of the control device in FIG. 4, FIG. 6 is a circuit diagram showing a specific example of the gain control device, and FIG. FIG. 8 is a block diagram showing another embodiment of the invention, FIG. 8 is a diagram showing the stored contents of a radio receiver having a memory preset function according to the invention, and FIG. 9 is a block diagram of the memory. 5...Tuning selection device, 10...Control device, 14...
Level detector, 15... Interference reducing means (gain control device), 16... Display device, 17... Muting circuit, 18... Switch.

Claims (1)

[Claims] 1. A high frequency amplification circuit that amplifies broadcast radio waves induced in an antenna, a local oscillation circuit, a mixer circuit that mixes output signals of the high frequency amplification circuit and the local oscillation circuit and converts the mixture into an intermediate frequency signal, and the mixer circuit. an intermediate frequency amplification circuit that amplifies the intermediate frequency signal of the intermediate frequency amplification circuit; a detection circuit that detects the intermediate frequency signal of the intermediate frequency amplification circuit; and a tuning device that controls the oscillation frequency of the local oscillation circuit and tunes the broadcast radio wave. ,
an intermodulation interference reduction device that is provided upstream of the mixer circuit and that reduces intermodulation interference output given to the desired broadcast radio wave selected by the channel selection device; and a muting device that mutates the output of the detection circuit. A radio receiver comprising a circuit, a level detector for detecting the input intensity of the broadcast radio wave, and a control device coupled to the channel selection device, the level detector, the muting circuit, and the intermodulation interference reduction device. , the control device controls the channel selection device and searches for the presence or absence of a first broadcast wave at a predetermined level within a predetermined band centered on the desired reception frequency by identifying the output of the level detector, and When there is no broadcast radio wave other than the desired reception frequency within a predetermined band, the tuning device is set to the desired reception frequency, and when there is a broadcast radio wave, the desired reception frequency is set in combination with the first broadcast radio wave. When the second broadcast radio wave is absent or is below a predetermined level, the channel selection device is set to the desired receiving frequency, and the second broadcast radio wave is detected. When the level is above the predetermined level, the intermodulation interference reducing device is driven to reduce the intermodulation interference output, and the control device is configured to receive the desired reception frequency in such a state, and the control device is configured to at least reduce the intermodulation interference broadcast radio wave. The radio reception is characterized in that the muting circuit is configured to control the muting circuit so as not to output unnecessary sound from the time when the operation of detecting the presence or absence of the signal is started until the broadcast radio waves of the desired reception frequency are received. Machine muting device.