JP2000174652A - Fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FM receiver capable of preventing the intrusion of noise by image interference and reducing tracking errors over the wide range of a reception frequency. SOLUTION: In this FM receiver, when an up key or the like of an operation part 83 is pressed and the change of the reception frequency is instructed, a CPU 81 changes the variable frequency division ratio of a frequency divider 32 and executes the change processing of the reception frequency owing to upper side oscillation. Then, the CPU 81 checks whether or not the image interference is generated by using the local oscillation signals of the upper side oscillation, and in the case that the image interference is generated, generates a tuning voltage provided with the same value as a VCO(voltage controlled oscillator) control voltage generated at the point of time, applies it to an RF reception circuit 2, then changes the variable frequency division ratio of the frequency divider 32 to the value for lower side oscillation and continues the reception of the broadcasting waves of the same reception frequency as the one before the change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver for receiving FM broadcast waves transmitted from FM broadcast stations in various countries.

[0002]

2. Description of the Related Art At present, the frequency bands of FM broadcast waves in various countries around the world are 76.0 to 90.0 MHz in Japan, 87.5 to 108.0 MHz in Europe and Australia, and 88.1 to 10 MHz in the United States.
7.9MHz, part of Eastern Europe is 65.0-74.0MHz
It has become. Since the frequency band of the United States is included in the frequency band of Europe, the frequency band of FM broadcast waves in each country is included in a range of approximately 65.0 to 108.0 MHz.

A general FM receiver employs a superheterodyne system, which converts a reception signal of a desired broadcast wave and a local oscillation signal into an intermediate frequency signal of 10.7 MHz, and then converts the signal into an FM signal. Various processes such as detection and stereo demodulation are performed. A local oscillation signal is used to convert the signal to the 10.7 MHz intermediate frequency signal.
In FM receivers in various countries, a local oscillation signal having a frequency that does not cause image interference is used. For example, in Japan, when a local oscillation signal having a frequency higher than the frequency of a broadcast wave is used, a video signal or an audio signal of a specific channel of a television broadcast appears near 10.7 MHz and image disturbance occurs. A local oscillation signal having a frequency lower than the frequency (hereinafter, a local oscillation signal having a frequency lower than the broadcast wave frequency is referred to as a “lower local oscillation signal”, and an oscillation operation for generating the lower local oscillation signal is referred to as a “lower local oscillation signal”. oscillation"
) Is used. In addition, in countries other than Japan described above, when a local oscillation signal having a frequency lower than the frequency of the broadcast wave is used, image interference occurs as in Japan, and therefore, in contrast to Japan, a frequency higher than the frequency of the broadcast wave is used. (Hereinafter, a local oscillation signal having a frequency higher than the frequency of the broadcast wave is referred to as an “upper local oscillation signal”, and an oscillation operation for generating the upper local oscillation signal is referred to as “upper oscillation”). .

[0004]

By the way, as described above, the FM receivers in each country use the lower local oscillation signal in Japan and the upper local oscillation signal in other countries. For this reason, there is a problem that image interference occurs when trying to receive broadcast waves of various countries using an FM receiver in which the local oscillation signal is set to one of the upper side and the lower side. For example, when receiving an FM broadcast in Japan using an FM receiver in which the local oscillation frequency is set to the upper side so that image interference does not occur in the United States or the like, image interference occurs depending on the reception frequency and is output. There is a case where the audio signal of the television broadcast is overlapped with the audio signal or noise based on the video signal is mixed.

Generally, when the reception frequency is changed by changing the frequency of the local oscillation signal, it is necessary to change the tuning frequency of the RF tuning circuit at the same time. Since the frequency of the intermediate frequency signal is shifted by 10.7 MHz, it is not easy to change these two frequencies in the same manner with a common control voltage. In particular, as described above, 65.0 to 10
If a broadcast wave is received over a wide range such as 8.0 MHz, there is a problem that a tracking error increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent FM from being mixed with noise due to image interference, and to reduce FM errors over a wide range of reception frequencies. To provide machines.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the FM receiver of the present invention basically transmits a broadcast wave by an upper oscillation which sets a frequency of a local oscillation signal higher than a reception frequency. With respect to the reception frequency at which image interference occurs, the broadcast wave is received by lower oscillation in which the frequency of the local oscillation signal is set lower than the reception frequency. For this reason, it is possible to prevent noises due to image interference from being mixed in all reception frequency bands, thereby enabling good reception of broadcast waves.

In order to switch between upper oscillation and lower oscillation depending on the presence or absence of image interference as described above, an image interference frequency specifying means for specifying a reception frequency at which image interference occurs when a broadcast wave is received by upper oscillation is provided. It is desirable to have. Since it is possible to easily determine whether or not the frequency of the broadcast wave actually received is a reception frequency at which image interference occurs, it is possible to reduce the processing load required for switching the frequency of the local oscillation signal. In particular, by retaining the reception frequency at which image interference occurs in the form of a table, it is possible to more easily determine whether or not a broadcast wave to be actually received causes image interference.

When a broadcast wave is received using the local oscillation signal on the upper side, a control voltage used for generating the local oscillation signal is also used as a tuning voltage applied to a high-frequency receiving circuit, and the local oscillation signal is used. When switching the signal, it is desirable that a tuning voltage having the same voltage value as the control voltage generated before the switching be generated separately from the control voltage and applied to the high-frequency receiving circuit. When the control voltage used to generate the local oscillation signal is also used as the tuning voltage, when the local oscillation signal is switched from the upper side to the lower side, the tuning voltage changes at the same time, and the reception frequency also changes. If a tuning voltage having the same voltage value as the control voltage before switching can be separately generated and the reception frequency can be set, the same broadcast wave can be received even when the local oscillation signal is switched.

In particular, as the tuning voltage generating means for generating the tuning voltage, it is desirable to use voltage holding means for holding the control voltage actually generated immediately before changing the local oscillation signal. Since the value of the actually generated control voltage can be used, the tuning voltage can be generated accurately and reliably. Alternatively, it is preferable to hold data on the control voltage generated immediately before changing the local oscillation signal, and generate the tuning voltage based on this data. For example, by holding the voltage value data of the tuning voltage corresponding to a specific reception frequency at which image interference occurs in the form of a table, or by holding the coefficients of a mathematical formula for calculating this tuning voltage by calculation, A desired tuning voltage can be obtained, and the configuration can be simplified.

It is preferable that a tracking error correcting means including at least a padding capacitor is provided. When the above-described control voltage is also used as a tuning voltage, there is a deviation of the intermediate frequency signal between the reception frequency and the local oscillation frequency, so that the tracking error increases as the reception frequency band increases. By correcting the tracking error by the correction means, the control voltage can be controlled in a wide reception frequency band including, for example, 65.0 to 108.0 MHz without performing complicated processing such as switching the tuning voltage in a complicated manner. , The receiving frequency can be changed in conjunction with, and the configuration can be simplified.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is shown in FIG.
The M receiver has a wide reception frequency band covering each broadcast wave in Europe, Australia, the United States, parts of Eastern Europe and Japan, and oscillates each broadcast wave excluding some broadcast waves in Japan. It is characterized by switching to lower oscillation for only some Japanese broadcast waves. Hereinafter, an FM receiver according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of an FM receiver according to the present embodiment. The FM receiver shown in FIG. 1 includes an RF receiving circuit 2, a local oscillator 3, a mixing circuit 4, an intermediate frequency amplifying circuit 5,
It is configured to include an FM detection circuit 6, a changeover switch 7, and a control unit 8.

The RF receiving circuit 2 performs a tuning operation for selectively passing only a component near a predetermined tuning frequency to a broadcast signal input from the antenna 1, and amplifies a high-frequency signal to the tuned signal. Do. FIG. 2 is a diagram illustrating a specific configuration of the RF receiving circuit 2. The RF receiving circuit 2 shown in FIG. 1 includes two harmonic tuning circuits 21 and 23 and a high frequency amplifier circuit 22. Antenna 1
The output of the first-stage high-frequency tuning circuit 21 to which is connected is amplified by the high-frequency amplifier circuit 22, and the amplified output is passed through the second-stage high-frequency tuning circuit 23, thereby improving selectivity. Each of the two high-frequency tuning circuits 21 and 23 includes a variable capacitance diode for changing the tuning frequency. By changing the reverse bias tuning voltage applied to these variable capacitance diodes, The tuning frequencies of the high-frequency tuning circuits 21 and 23 are changed in conjunction with each other.

The local oscillator 3 is a voltage controlled oscillator (VC
O) 31, a frequency divider 32, a reference signal generator 33, a phase comparator 34, and a low-pass filter (LPF) 35.

The VCO 31 oscillates at a frequency corresponding to the control voltage applied from the low-pass filter 35, and its output is input to the mixing circuit 4 as a local oscillation signal. The VCO 31 includes an amplifier 91 and a VCO resonance circuit 92, and performs an oscillation operation at a resonance frequency set by the VCO resonance circuit 92. The VCO resonance circuit 92 is basically a parallel resonance circuit composed of an inductor 93 and a capacitor 95, and variable capacitance diodes 96 and 97 for varying the frequency are connected in parallel with the capacitor 95, and a padding capacitor 94 for tracking adjustment is provided.
Are added in series with the inductor 93. The control voltage generated by the low-pass filter 35 is applied to the cathode terminals of the variable capacitance diodes 96 and 97 via the resistor 98, and the output from the VCO 31 is changed by changing the capacitance of the two variable capacitance diodes 96 and 97. The frequency of the local oscillation signal is changed. This VCO 31
Are also input to the frequency divider 32.

The frequency divider 32 has a variable frequency division ratio N set by the control of the control unit 8, and divides the signal input from the VCO 31 by the variable frequency division ratio N and outputs the resultant signal. The reference signal generator 33 outputs a reference signal of a predetermined frequency with high frequency stability. The phase comparator 34 compares the phase of this reference signal with the signal output from the frequency divider 32,
A pulse-shaped error signal corresponding to the phase difference is output. The low-pass filter 35 generates a control voltage by smoothing the error signal output from the phase comparator 34. VCO mentioned above
31, a dividing ratio 32, a phase comparator 34, and a low-pass filter 35 are connected in a loop to form a PLL (phase locked loop).
Is configured.

For example, the frequency of the reference signal output from the reference signal generator 33 is set to 100 kHz, and when receiving a broadcast wave having the reception frequency f, the frequency is 10.7 M higher than the reception frequency.
To generate the local oscillation signal higher by Hz, the variable frequency dividing ratio N of the frequency divider 32 may be set to (f + 10.7) × 10. Similarly, the reception frequency is 10.7 MH
In order to generate a lower local oscillation signal having a lower z, the variable frequency dividing ratio N of the frequency divider 32 may be set to (f-10.7) × 10.

The mixing circuit 4 mixes the tuned and amplified reception signal output from the RF reception circuit 2 with the local oscillation signal output from the local oscillator 3 and outputs a difference component and a sum component thereof. The intermediate frequency amplification circuit 5 includes the mixing circuit 4
10.7MHz while amplifying the signal output from
A tuning operation is performed to pass only nearby frequency components, and 1
An intermediate frequency signal of 0.7 MHz is output.

[0020] The reception frequency f, and the frequency of the local oscillation signal and f _0, f-f ₀ from the mixing circuit 4, f ₀ -f,
A signal including each component of f + f ₀ is output. Since the sum component f + f ₀ is always larger than 10.7 MHz, the 10.7 MHz intermediate frequency signal output from the intermediate frequency amplification circuit 5 has the reception frequency f
₀ + 10.7, will include only two components of f ₀ -10.7. Therefore, when the local oscillator 3 is oscillated on the upper side to extract a specific reception frequency (f ₀ -10.7) component, the other component (f ₀ +1) is always required.
0.7) is also extracted, but this component has been removed by passing through the tuning circuits 21 and 23 in the RF receiving circuit 2, and eventually an intermediate frequency signal corresponding to a broadcast wave having a desired frequency is extracted. . The same is true if you try to extract a particular receive frequency (f ₀ +10.7) components by oscillating the local oscillator 3 in the lower, always other components (f ₀ -1
0.7) is also extracted, but this component has been removed by passing through the tuning circuits 21 and 23 in the RF receiving circuit 2, and eventually an intermediate frequency signal corresponding to a broadcast wave having a desired frequency is extracted. .

The FM detection circuit 6 performs a detection process on the intermediate frequency signal output from the intermediate frequency amplification circuit 5 and outputs a composite signal. Note that this FM detection circuit 6
At the subsequent stage, a stereo demodulation circuit (not shown) or the like is connected, and the L signal and the R signal included in the composite signal are separated and amplified, and output from separate speakers.

The changeover switch 7 switches the supply source of the tuning voltage applied to the RF receiving circuit 2. When the local oscillator 3 performs upper oscillation, the local oscillator 3 applies a voltage from the low-pass filter 35 to the VCO 31. The selected control voltage is directly selected as the tuning voltage and applied to the RF receiving circuit 2. In addition, when lower oscillation is performed by the local oscillator 3, a tuning voltage generated by the controller 8 is selected and applied to the RF receiving circuit 2.

The control section 8 controls the entire FM receiver. For example, setting of the reception frequency by setting the variable frequency division ratio N of the frequency divider 32 in the local oscillator 3 described above,
The control of the changeover switch 7 is performed by the control unit 8. The control unit 8 includes a CPU 81, a memory 82,
Operation unit 83, analog-digital (A / D) converter 8
4. It is configured to include a digital-analog (D / A) converter 85.

The CPU 81 performs a predetermined control operation by executing an operation program stored in the memory 82. The memory 82 has, in addition to this operation program,
Various data including a lower oscillation data table necessary for specifying a frequency at which the local oscillator 3 switches to the lower oscillation is stored. The A / D converter 84 converts the control voltage output from the low-pass filter 35 into digital data and outputs the digital data to the CPU 81. Further, the D / A converter 85 generates a tuning voltage based on data output from the CPU 81. The operation unit 83 includes various keys such as an up key, a down key, and a volume key for adjusting a volume, which change the reception frequency of the FM broadcast wave to a higher or lower frequency, and is provided by a user. The operation instruction such as the selected channel is output to the CPU 81. The user can select an FM broadcast wave to be received by increasing or decreasing the reception frequency by 0.1 MHz by pressing an up key or a down key provided on the operation unit 83.

The above-described RF receiving circuit 2 serves as a high-frequency receiving circuit, the control section 8 serves as control means, and the CPU 81 and the memory 8
2 is a CPU 81, A /
The D converter 84 and the D / A converter 85 correspond to a tuning voltage generation unit and a voltage holding unit, the changeover switch 7 corresponds to a switching unit, and the padding capacitor 94 corresponds to a correction unit.

The FM receiver of the present embodiment has such a configuration, and its operation will be described next.

FIG. 3 shows the reception frequency f and the local oscillation frequency f.
FIG. 9 is a diagram illustrating a relationship of ₀ . As shown in FIG. 3, the FM receiver according to the present embodiment has a lower frequency of 65 MHz and a higher frequency of 108 MHz.
covering the reception frequency up to z, and over almost all but a part of this wide reception frequency band,
Local oscillation frequency f ₀ is 10.7 MH higher than reception frequency f
The upper oscillation set at z higher is performed. For this reason, it is possible to secure a good reception state free from image disturbance in Europe, the United States, and the like except Japan. In addition, when the upper oscillation is used, some of the broadcast waves in Japan are received because the video signal and the audio signal of the television broadcast interfere with the image and the noise is mixed into the output sound. Only when this is done, the upper oscillation is switched to the lower oscillation to receive the broadcast wave.

FIG. 4 is a diagram showing the specific storage contents of the lower oscillation data table in which the reception frequencies of some broadcast waves in Japan where image interference occurs when the upper oscillation is performed. When the upper oscillation is performed, image interference actually occurs because (1) 80.3 corresponding to the audio frequency 101.75 MHz of two channels of the television broadcast.
And (2) a reception frequency of 81.7 to 82.0 MHz corresponding to a video frequency of 103.25 MHz of three channels of television broadcasting.
(3) Audio frequency 1 of two channels of television broadcasting
86.3-86.4 MHz corresponding to 01.75 MHz
Is increased. Actually, the reception frequency of the broadcast wave is assigned every 0.1 MHz, and thus, as shown in FIG. 4, eight specific frequencies are specified as the reception frequencies at which image interference occurs. Therefore, the CPU 81
Is to switch the reception method that has been received by the upper oscillation to the lower oscillation when trying to receive a broadcast wave of any reception frequency included in the lower oscillation data table stored in the memory 82. Accordingly, occurrence of image disturbance can be prevented.

By the way, when a part of the broadcast wave in Japan is received as described above, the occurrence of image disturbance can be prevented by switching the reception method using the upper oscillation to the reception method using the lower oscillation, which has been performed so far. However, inconvenience occurs when the control voltage for upper oscillation applied to the VCO 31 is also used as the tuning voltage of the RF receiving circuit 2 as in the FM receiver shown in FIG. That is, when the control voltage generated for the upper oscillation is switched to the control voltage for the lower oscillation, the tuning frequency of the RF receiving circuit 2 is simultaneously switched. To avoid such inconvenience,
In the FM receiver of the present embodiment, when the local oscillator 3 is switched to the lower oscillation, the control voltage generated by the control unit 8 is applied to the RF receiving circuit 2.

FIG. 5 is a diagram showing the relationship between the control voltage V _C applied to the VCO 31 in the local oscillator 3 and the tuning voltage V _T applied to the RF receiving circuit 2. As mentioned above,
Control is performed so that the oscillation frequency of the VCO 31 is partially reduced by 10.7 × 2 (= 21.4) MHz because the oscillation is partially switched from the upper oscillation to the lower oscillation in order to receive some Japanese broadcast waves. the voltage V _C changes. On the other hand, the tuning voltage V _T
Is generated partially by the control unit 8 even when the oscillation is switched from the upper oscillation to the lower oscillation, and its continuity is maintained.

FIG. 6 is a flowchart showing an operation procedure of the FM receiver for switching the upper oscillation to the lower oscillation according to the reception frequency. The CPU 81 constantly monitors whether or not the user has operated the operation unit 83 to instruct an instruction to change the frequency (step 100). If the instruction to change the frequency is not issued, the CPU 81 maintains the current reception state. For example, if any broadcast wave is being received, the receiving operation is maintained.

When the user presses a frequency change key such as an up key or a down key included in the operation section 83 by the user, the CPU 81 next performs a frequency change operation in accordance with the key operation. The frequency division ratio after the change for the upper side oscillation is calculated and set as the variable frequency division ratio of the frequency divider 32 (step 101). For example, assuming that the up key is pressed to change the reception frequency to a higher one, the frequency division ratio corresponding to the reception frequency after the frequency change is calculated according to the number of times the up key is pressed. Regardless of whether or not this reception frequency is included in the lower oscillation data table shown in FIG. 4, the frequency division ratio of frequency divider 32 is temporarily set to the frequency division ratio for upper oscillation. . When a new variable frequency division ratio N of the frequency divider 32 is set in this way, a new control voltage is applied to the VCO 31 and this control voltage is also applied to the RF receiving circuit 2 as a tuning voltage. , The reception frequency is changed to 0.1 × N-10.7 MHz (step 102).

Next, the CPU 81 determines whether or not it is necessary to switch to the lower oscillation for the changed reception frequency (step 103). This determination is made by checking whether or not the changed reception frequency matches any of the reception frequencies included in the lower oscillation data table shown in FIG. If it does not match any of the reception frequencies, even if the broadcast wave of the reception frequency after the change is received by the upper oscillation, there is no image disturbance,
Returning to step 100 described above, the changed reception state is maintained.

If the changed reception frequency matches any of the reception frequencies included in the lower oscillation data table shown in FIG. 4, an affirmative determination is made in step 103, and the CPU 81 then proceeds to step 103. The control voltage applied to the VCO 31 for the later reception frequency is converted into an A / D converter 8
4, after converting the digital data into digital data and capturing it (step 104), the captured data is input to a D / A converter 85, and a tuning voltage having the same voltage value as the captured control voltage is converted to a D / A converter. 85 (step 105). Next, the CPU 81 switches the changeover switch 7 to set the output terminal of the D / A converter 85 to RF.
Connect to the receiving circuit 2 and apply the tuning voltage generated by the D / A converter 85 to the RF receiving circuit 2 (Step 1)
06). Before and after the changeover switch 7 is switched, the value of the tuning voltage applied to the RF receiving circuit 2 does not change, so that the tuning frequency in the RF receiving circuit 2 maintains the same value.

Next, the CPU 81 calculates a division ratio N 'for lower oscillation corresponding to the same reception frequency, and
(Step 107). When the division ratio for the upper oscillation is N, the reception frequency f is 0.1 × N
However, in order to realize the reception frequency f by lower oscillation, f = 0.1 × N ′ + 10.7 holds. Therefore, between the newly set division ratio N 'for lower oscillation and the division ratio N for upper oscillation before change, N'
= N-214, and the dividing ratio N before the change is 21
A value obtained by subtracting 4 may be set as a new frequency division ratio N '. Thus, the oscillation is changed to the lower oscillation without changing the tuning frequency of the RF receiving circuit 2. Thereafter, the process returns to step 100 described above to maintain the changed reception state.

As described above, the FM receiver according to the present embodiment
Basically, the local oscillation frequency is set to the upper side of the reception frequency to receive the broadcast wave, and the local oscillation frequency is switched to the lower side only when a broadcast wave of a specific reception frequency causing image interference is received. Therefore, it is possible to prevent noise from being mixed in each broadcast wave within the reception frequency band due to occurrence of image disturbance.

Further, even when the control voltage actually applied to the VCO 31 varies depending on each reception frequency at which image interference occurs, the actual voltage value is taken in and the tuning voltage having the same value is obtained. Since it is generated, R
The tuning voltage applied to the F receiving circuit 2 can be generated simply and reliably. In particular, the above-described operation can be performed only by adding the A / D converter 84, the D / A converter 85, and the changeover switch 7, and the occurrence of image disturbance can be prevented with a simple configuration. Also, the A / D converter 84
Some CPUs have a built-in CPU and the like, and when such a CPU is used, the configuration of the present embodiment can be realized with almost no additional components.

The VCO resonance circuit 92 in the VCO 31
By including a padding capacitor 94 in the
The frequency of the local oscillation signal output from the VCO 31 and the tuning frequency of the RF receiving circuit 2 can be made to accurately follow over the entire wide receiving band of 5.0 to 108.0 MHz, and a small tracking error is realized. Can be.

Since only the eight reception frequencies shown in FIG. 4 can be switched to lower oscillation, the A / D converter 84 having a narrow input voltage allowable range and the D / A converter having a narrow output voltage variable range are provided. Since 85 can be used, an increase in component cost can be suppressed as much as possible.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the above-described embodiment, before switching to the control voltage for lower oscillation, the value of the control voltage for upper oscillation is converted into digital data and taken in, and then the digital data is again converted to analog voltage. Although the tuning voltage having the same value as the captured control voltage is generated, the tuning voltage may be generated by holding the captured control voltage using an analog voltage holding circuit. FIG. 7 is a diagram illustrating an example of an analog voltage holding circuit.
The voltage holding circuit shown in FIG. 1 includes an operational amplifier 100, a switch 101, and capacitors 102 and 103. When the switch 101 is turned on, the control voltage, which is the output of the low-pass filter 35, is applied to the capacitors 102, 10
3, charges corresponding to the magnitude of the control voltage are stored in these capacitors 102 and 103.
Thereafter, when the switch 101 is turned off, the capacitor 10
Since the control voltage, which is the voltage between both ends of the switch 3, is held, the held control voltage is used as the tuning voltage and the changeover switch 7
May be applied to the RF receiving circuit 2 via the.

Further, instead of generating the tuning voltage for the lower oscillation while holding the control voltage for the immediately preceding upper oscillation, the corresponding tuning voltage may be generated using a table or a mathematical expression. . For example, tuning voltage data corresponding to each reception frequency included in the lower oscillation data table shown in FIG. 4 is stored in the memory 82 as a table, or the tuning voltage data is included in the lower oscillation data table. When switching to lower oscillation corresponding to any of the reception frequencies, the tuning voltage data may be input to the D / A converter 85 to generate a corresponding tuning voltage. Further, as shown in FIG. 5, in order to generate a tuning voltage corresponding to a reception frequency included in a very narrow range, the relationship between the reception frequency and the tuning voltage is approximated by a simple equation, for example, a linear equation, and only the coefficient is obtained. Is stored in the memory 82, and when switching to lower oscillation, a tuning voltage is calculated using this coefficient, and the calculation result is input to the D / A converter 85 to generate a corresponding tuning voltage. You may do so.
If the above table or formula is used, VCO
Since the A / D converter 84 used for taking in the control voltage is not required, the configuration can be simplified.

[0042]

As described above, according to the present invention, the broadcast wave is received by the upper oscillation that normally sets the frequency of the local oscillation signal higher than the reception frequency. Since the broadcast wave is received by the lower oscillation that sets the frequency of the oscillating signal lower than the reception frequency, it is possible to prevent the noise from being mixed in due to image interference in all the reception frequency bands and to receive the broadcast wave well. Become.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an FM receiver according to an embodiment.

FIG. 2 is a diagram illustrating a specific configuration of an RF receiving circuit.

FIG. 3 is a diagram illustrating a relationship between a reception frequency and a local oscillation frequency.

FIG. 4 is a diagram showing contents of a lower oscillation data table stored in a memory.

FIG. 5 is a diagram showing a relationship between a control voltage and a tuning voltage.

FIG. 6 is a flowchart illustrating an operation procedure of an FM receiver that switches upper oscillation to lower oscillation according to a reception frequency.

FIG. 7 is a diagram illustrating a configuration of an analog voltage holding circuit.

[Explanation of symbols]

 Reference Signs List 2 RF reception circuit 3 Local oscillator 7 Changeover switch 8 Control unit 31 VCO (voltage controlled oscillator) 81 CPU 82 Memory 84 A / D converter 85 D / A converter 92 VCO resonance circuit 94 Padding capacitor

Claims (8)

[Claims] A high-frequency receiving circuit for selectively amplifying an FM broadcast wave having a receiving frequency according to a tuning voltage; a local oscillator generating a local oscillation signal having a frequency according to a control voltage; A mixing circuit that mixes each output signal of the local oscillator to generate an intermediate frequency signal; an intermediate frequency amplification circuit that selectively amplifies a predetermined frequency component with respect to the intermediate frequency signal output from the mixing circuit; While controlling the frequency of the local oscillation signal to be higher than the reception frequency to control the reception of the broadcast wave, if image interference occurs in the reception signal, the frequency of the local oscillation signal is set higher than the reception frequency. Control means for receiving the same broadcast wave at a low setting, and performing control to maintain the tuning voltage at substantially the same value before and after changing the local oscillation signal. FM receiver, wherein the door. 2. The image interference frequency specifying means according to claim 1, wherein the frequency of the local oscillation signal is set higher than the reception frequency and the reception frequency at which image interference occurs when the broadcast wave is received is specified. An FM receiver, further comprising: 3. The image interference frequency identification unit according to claim 2, wherein the image interference frequency identification means has a table including the reception frequency at which image interference occurs.
An FM receiver, which determines that image interference occurs in the received signal when the currently set reception frequency matches any of the reception frequencies included in the table. 4. The tuning voltage generation means according to claim 1, wherein the tuning voltage has substantially the same voltage value as the control voltage generated immediately before changing the local oscillation signal. When the frequency of the local oscillation signal is set higher than the reception frequency and the broadcast wave is received, the control voltage is applied to the high-frequency reception circuit as the tuning voltage, and the frequency of the local oscillation signal is set to the reception frequency. Switching means for switching the tuning voltage generated by the tuning voltage generating means to be applied to the high-frequency receiving circuit when the broadcast wave is received at a lower setting. Receiving machine. 5. The FM receiver according to claim 4, wherein the tuning voltage generating means has a voltage holding means for holding the control voltage actually generated immediately before changing the local oscillation signal. . 6. The tuning voltage generator according to claim 4, wherein the tuning voltage generating means has data on the control voltage generated immediately before changing the local oscillation signal, and generates the tuning voltage based on the data. An FM receiver, comprising: 7. The FM receiver according to claim 1, further comprising a correction unit that includes at least a padding capacitor and corrects a tracking error in an FM reception frequency band. 8. The FM reception frequency band according to claim 7, wherein the FM reception frequency band is at least 65 MHz to 1 MHz.
An FM receiver comprising 08 MHz.