JPS6312406B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a radio receiver, and more particularly, the present invention relates to a radio receiver.
Using a microcomputer, etc., it searches for and calculates the presence and strength of other broadcast radio waves that have frequencies that can cause intermodulation interference to the desired receiving frequency, and when the results indicate that they exist, reduces the intermodulation interference output of the receiver. This is related to a radio receiver. FM radio broadcasts are widely enjoyed due to their good sound quality, but as the number of broadcasting stations increases, interference has become a serious problem in which the sound quality of the desired broadcast is impaired by radio waves other than the desired broadcast. . In particular, intermodulation interference is desired to be improved because it causes an unpleasant "jerky" sound due to beats with the desired received signal. 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 radio waves, and 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 the amplifying element has nonlinearity as expressed by the following 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 ₁ and ₂ , 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 , v ₂ becomes the signal voltage of ₁ , 2 _{ω 1 ;} 2π ₁ , ω ₂ ; 2π 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(2 ₁ − ₂ )t ……(3) 3/4a ₃ v ₁ v ₂ ² sin2π(2 ₂ − ₁ ) t ₁ ...(4) This includes the spectrum. In this case, if ₂ = ₁ + Δ, the spectra of equations (3) and (4) will occur at ₁ - Δ and ₁ + 2 Δ, as shown by the broken lines in FIG. Therefore, if the receiving frequency of the receiver is tuned to ₁ - Δ or ₁ + 2 Δ, a mixture of broadcast content of ₁ and ₂ ( ₁ + Δ) will be received even if there is no signal there. become. As a means to solve this problem, the present applicant has previously proposed a radio receiver that is equipped with a control device having arithmetic functions such as a microcomputer to improve intermodulation interference. FIG. 2 is a block diagram of the proposed device. In FIG. 2, broadcast radio waves (signals) induced in an antenna 1 are transmitted through a frequency selection circuit 2, a high frequency amplification circuit 3, and a frequency selection circuit 4.
is led to the mixer circuit 5 through the local oscillator circuit 6.
is mixed with the output from and converted to an intermediate frequency,
This converted signal is demodulated through an intermediate frequency filter 7, an intermediate frequency amplification circuit 8, and an FM detection circuit 10. These constitute the well-known superheterodyne receiver. The local oscillation circuit 6 includes a reference signal generator 15 that oscillates a stable reference frequency r based on a crystal oscillator 16, a voltage controlled oscillator (VCO) 11, and an oscillation frequency l of this VCO. 1/N
A programmable divider 12 that divides the frequency into It consists of a phase comparator (φ) 13 and a low-pass filter (LPF) 14 that smooths the output voltage of this phase comparator to extract a continuous voltage component proportional to the phase difference and guides it to the VCO 11. constitutes a generally well-known PLL (Phase Lock Loop) circuit. That is, the output frequency l of the VCO 11 is divided into 1/N by the programmable divider 12 controlled by the control device 17, and the output frequency of this divider 12 becomes l/N, which is the output frequency r of the reference signal generator 15. The phase is compared with the phase comparator 13, and the VCO
11 control is performed, and the output of VCO 11 is l
It is held at a value of =N·r. Here, if the output frequency r of the reference signal generator 15 is set to r=100 kHz, for example, then by changing the frequency division ratio N of the programmable divider 12, reception at every 100 kHz step becomes possible. The control device 17 consists of a program section (program memory) 21 that stores programs for channel selection and intermodulation interfering broadcast wave discrimination, an arithmetic processing section 20 that performs arithmetic processing, and a storage device 22, and uses the operation keys of the operation keyboard 19. Control is performed according to a program stored in the program section 21 in response to a command generated by an operator's operation. A level detector 9 is connected between the intermediate frequency amplification circuit 8 and the arithmetic processing section 20, and detects when the reception level of the receiver reaches a certain level. Reference numeral 18 denotes a gain control device connected between the antenna 1 and the frequency selection circuit 2 of the receiver, and this device variably controls the gain of the receiver based on the output signal of the arithmetic processing section 20. Details of the operation keyboard 19 are shown in FIG. Figure 3 shows the tuning section of the front panel of the radio receiver. In Figure 3, 23 is a down tuning key that lowers the reception frequency each time it is operated;
Reference numeral 24 indicates an up channel selection key, and reference numeral 25 indicates a preset channel key for controlling writing and reading. Reference numeral 26 denotes a memory switch that enables presetting. By operating this switch, the memory becomes ready for writing. After specifying the preset channel and completing the writing, the next time, by operating the preset channel key 25, the memory switch becomes ready for writing. Can be read. 27 is an IM processing operation (the control device 17 in FIG. 2 controls the channel selection, that is, the local oscillation frequency of the local oscillation circuit 6 to change the reception frequency, and the level detector 9 detects interference radio waves that interfere with the desired reception frequency). A series of steps for searching for the presence or absence of two broadcast radio waves with frequencies that can cause intermodulation interference with the desired receiving frequency, and applying a control signal from the arithmetic processing unit 20 to the gain control device 18 according to the search results to perform gain control. This is an IM processing instruction key that instructs the operation (hereinafter referred to as IM processing operation), and consists of a momentary switch that is electrically connected only when operated. Reference numeral 28 is a display section for displaying frequencies, and 29 is a front panel of the radio receiver on which an operation keyboard 19 is arranged. FIG. 4 shows an example of the configuration of the gain control device 18.
This drives the transistor 32 via the resistor 33 with a control signal from the control device 17, and the pin
A current is passed through the diodes 30 and 31 from the power supply +B to reduce the operating resistance of the pin diode, thereby controlling the gain of the input signal from the antenna 1. In addition, 34 is a resistance, 35, 3
6 and 37 are capacitors. Next, the operation of the radio receiver shown in FIG. 2 will be explained. After the desired reception frequency is specified by operating the channel selection key (for example, UP channel selection key 24) on the operation keyboard 19, when the IM processing instruction key 27 for instructing IM processing operation is operated, the control device 17 is the spectrum generated by intermodulation between the first radio wave ₁ and the second radio wave ₂ ( ₁ + Δ) other than the desired reception frequency described in Fig. 1, which has a predetermined relationship with the desired reception frequency ( ₁ −Δ
Alternatively, by controlling the programmable divider 12 with the control device 17, the programmable divider 12 is controlled by the control device 17 to determine whether or not there is an interfering radio wave whose ₁ + 2 Δ) matches the desired reception frequency and causes interference. The level detector 9 detects the search information (IM).
information) to send a control signal to the gain control device 18 to perform gain control and reduce intermodulation interference. By the way, as shown in FIG. 5, the frequency selection circuits 2 and 4 are circuits that have a characteristic that the attenuation increases as the input frequency moves away from the desired frequency s, so if the strength of the interfering radio waves is constant, Then, the level of the interference radio waves at the input of the high-frequency amplifier circuit 3 and the mixer circuit 5 becomes smaller as the interference radio waves are farther away from the desired receiving frequency, and therefore, the level of the interference radio waves generated in the high-frequency amplifier circuit 3 and the mixer circuit 5 becomes The magnitude of intermodulation becomes smaller as the interfering radio waves are farther away from the desired reception frequency. For example, the magnitude of intermodulation is as shown in equations (3) and (4),
Since it is proportional to v ₁ ² v ₂ or v ₁ v ₂ ² , frequency selection circuits 2 and 4 reduce v ₁ to 10 dB and v ₂ to 20 dB (in fact, interference radio waves approximately 1 MHz away from the desired receiving frequency are Interfering radio waves of 10 dB or more and about 2 MHz away will be attenuated by 20 dB or more).
Intermodulation is improved by more decibels. Therefore, performing a certain amount of gain control using the gain control device 18 as shown in FIG. 4, regardless of the frequency difference between the desired reception frequency and the interfering radio waves, is more effective than improving the intermodulation interference. This results in the inconvenience of having to perform input gain control. An object of the present invention is to eliminate the inconvenience of having to perform antenna input gain control more than improving intermodulation interference in the prior art described above, and to perform better interference cancellation than in the past. It is possible to provide a radio receiver. In order to achieve the above object, the features of the present invention are as follows:
The antenna input gain control value in the gain control device (18 in FIG. 2) is changed in accordance with the frequency difference between the desired reception frequency and the interfering radio wave (intermodulation interfering broadcast wave). The present invention will be explained below with reference to the drawings. FIG. 6 is a block diagram showing one embodiment of the present invention. In FIG. 6, 40 is connected between the antenna 1 and the frequency selection circuit 2, and is a control signal AT/
0, AT.1, . . . , AT.n, AT.n+1, and the other symbols are the same as in FIG. 2.

[Table] Table 1 shows the two broadcast radio waves (frequency ₁ ,
₂ ) and the desired broadcast radio wave (frequency s) into several ranges, and the control device 17 attempts to change the gain control value in the gain control device 40 according to each divided range. This is a classification table of control signals in which the frequency difference increases in the order of Δ ₁ , Δ ₂ , ..., Δ _o . Control signal AT・1～
AT·n+1 is a control signal corresponding to the frequency difference Δ in each division range. FIG. 7 shows a circuit diagram of an embodiment of the gain control device 40. The difference from the conventional example shown in FIG. 4 is that the resistance at the base end of the transistor 32 is a parallel connected resistance 38 ₁ ,
This is the point replaced by 38 ₂ , . . . , 38 _o+1 . In FIG. 7, the signal from antenna 1 is
When there is no interfering radio wave, the control signal is not output from the control device 17 and is output as is without being subjected to gain control. When there is interference, the control device 17
control signal AT・i (where i=1, 2, . . .
n, n+1) is output, the transistor 32 is driven through the resistor 38i, and the pin diode 3
A current flows from the power supply +B to 0 and 31, and the operating resistance of the pin diode decreases, so that the output is subjected to gain control. The amount of attenuation of the antenna input signal due to gain control is AT・1, AT・2,...
It is configured to become smaller in the order of AT・n and AT・n+1. In other words, the gain control amount of the gain control device 40 is configured to become smaller as the frequency difference Δ becomes larger. FIG. 8 shows how the operation keyboard 19 is operated by the user.
It shows an example of the processing flow of the control device 17 when the IM processing instruction key 27 is operated. The operation of the embodiment shown in FIG. 6 will be described below with reference to the flow shown in FIG. 8, FIGS. 3 and 7, and Table 1. When the desired reception frequency s is specified by operating the channel selection key (for example, the UP channel selection key 24) on the operation keyboard 19, the control device 17 activates the arithmetic processing unit 20.
Based on the process shown in FIG. 8, a tuning control value for variable control of the local oscillation frequency of the local oscillation circuit, that is, a frequency division ratio N ₀ corresponding to the frequency is calculated. this
N ₀ is stored in the storage section 22 ₃ of the storage device 22 and is input to the programmable divider 12 .
As a result, the local oscillation circuit 6 is activated in a well-known manner.
PLL operation is performed, and the receiving frequency of the receiver is set to s. During the processing process, the operation keyboard 1
If the IM processing instruction key 27 of 9 is not operated, the process will proceed to the next process, but if the instruction key 27 is operated, the process will proceed to the process, where 1 will be added to _N0 , and this value will be stored in advance during the process. A determination is made as to whether or not the value exceeds a value corresponding to the upper limit frequency of the receiving band stored in the storage unit 22 ₁ of the device 22 . If it is within the reception band, input this value into the programmable divider 12 during the processing process,
Raise the reception frequency by one step (for example, 100kHz),
At this frequency, the presence or absence of the output of the level detector 9 is determined through the arithmetic processing unit 20, and the presence or absence of broadcasting is checked. If there is no broadcast, return to the processing process and repeat 1 more
and perform the same operation. If there is a broadcast in the processing process, the arithmetic processing unit 20 stores this value in the storage unit ₂₂₄ of the storage device 22, and based on the processing process, it stores the currently received receiving frequency (corresponding value N) and the desired receiving frequency (corresponding value N). The frequency difference (ΔN=N−N ₀ ) with respect to the value N ₀ ) is calculated by subtracting the value in the storage unit 22 ₃ from the value in the storage unit 22 ₄ , and stored in the storage unit 22 ₅ for processing. In the process, a frequency (corresponding value N ₀ +2ΔN) that causes intermodulation interference is calculated. In the processing process, as in the processing process, it is determined whether this frequency is within the reception band. If it is outside the reception band, the process returns to the process. If it is within the receiving band during the processing process,
Let's move on to the processing process. If there is a broadcast in the processing process, it means that there is a broadcast with a frequency relationship that causes intermodulation interference.
0 reads the frequency difference Δ from the storage unit ₂₂₅ , calculates which classification range shown in Table 1 this frequency difference belongs to, outputs a control signal corresponding to the calculated classification range, and outputs a control signal corresponding to the calculated classification range. In response to this, the gain control device 40 performs control to lower the gain of the antenna input according to the frequency difference between the desired reception frequency s and the interfering radio wave based on the processing process, and inputs N ₀ to the programmable divider 12 in the processing process to control reception. Complete the operation and receive the desired reception frequency s. If the reception band is exceeded during the processing process, it means that the search up to the upper limit frequency has been completed, and the process returns to the desired reception frequency s and returns to the processing ~
A search is performed in the same manner as above toward the opposite side, that is, toward the lower limit frequency. The lower limit frequency of the reception band is stored in advance in the storage unit 22 ₂ of the storage device 22 . Processing process~ is the above-mentioned processing process~
, and its detailed explanation will be omitted. If it is outside the reception band in the processing process, it means that the search to the lower limit frequency has been completed, and there is no interfering radio wave that causes interference at the desired reception frequency s, and the process moves on to the desired reception frequency s. receive. As explained above, according to the present invention, the gain control device controls the gain according to the frequency difference between a desired reception frequency and two broadcast waves (jamming waves) that cause intermodulation interference at this desired reception frequency. By configuring the control device to generate multiple control signals that change their values, the antenna gain control is performed more than improving intermodulation interference when the interfering radio waves are far enough away from the desired receiving frequency. It is possible to eliminate the inconvenience of interference, thereby achieving better interference removal than in the past.

[Brief explanation of the drawing]

Figure 1 is a frequency spectrum diagram to explain intermodulation interference, Figure 2 is a device block diagram, Figure 3 is a detailed diagram of the operating keyboard, Figure 4 is a circuit diagram of the gain control device, and Figure 5 is frequency selection. 6 is a block diagram of an embodiment of the present invention, FIG. 7 is a circuit diagram of the gain control device in FIG. 6, and FIG. 8 is a processing flow diagram showing the operation of FIG. 6. . Explanation of symbols, 1...Antenna, 2, 4...Frequency selection circuit, 5...Mixer circuit, 6...Local oscillation circuit, 8...Intermediate frequency amplification circuit, 9...Level detector, 10...FM Detection circuit, 11... Voltage controlled oscillator, 12... Programmable divider, 13
...Phase comparator, 14...Low pass filter, 15...
...Reference signal generator, 17...Control device, 18,4
0...gain control device, 19...operation keyboard,
20... Arithmetic processing unit, 21... Program memory, 22... Storage device, 23, 24... Tuning selection key, 25... Preset channel key, 26...
...Memory switch, 27...IM processing instruction key,
28...Display section, 29...Front panel.

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; a gain control device that is provided after the antenna and that varies the gain of the antenna input; A radio receiver comprising: a level detector for detecting the input level of broadcast radio waves; and a control device for controlling the local oscillation frequency of the local oscillation circuit, tuning the broadcast radio waves, and controlling the gain control device. , the control device includes a program section storing a program for discriminating channel selection and intermodulation interfering broadcast waves, and a program section that calculates a channel selection control value for variably controlling the local oscillation frequency of the local oscillation circuit according to the program of the program section. Variable the local oscillation frequency,
The presence or absence of two broadcast radio waves having frequencies that can cause intermodulation interference to the desired receiving frequency of the desired broadcast radio wave is searched for through the level detector, and if the search results indicate that there is an intermodulation interfering broadcast radio wave, intermodulation interference is detected. an arithmetic processing unit that controls the gain control device so that the output is reduced and varies a gain control value of the gain control device according to a frequency difference between the desired reception frequency of the broadcast wave and the frequency of the intermodulation interfering broadcast radio wave; and a storage device that stores the tuning control value calculated by the arithmetic processing section.