JP3213087B2 - Automatic channel selection method and receiver for receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver,
In particular, the present invention relates to a method for automatically selecting a radio receiver in a vehicle.

[0002]

2. Description of the Related Art A technique of a conventional AM receiver will be described with reference to FIG. FIG. 6 shows a block diagram of an AM receiver according to the prior art. In FIG. 6, a high-frequency amplifier circuit 1 amplifies a received signal. Local oscillation circuit 4 oscillates at a predetermined local oscillation frequency. The mixer circuit 2 converts the local oscillation signal from the local oscillation circuit 4 and the amplified reception signal and outputs an intermediate frequency signal. The intermediate frequency amplifier circuit 3 amplifies the intermediate frequency signal from the mixer circuit 2,
The frequency information of the amplified intermediate frequency signal is output from the intermediate frequency signal output terminal 8, and the signal strength information is output from the signal strength output terminal 9. A microcomputer 5 (hereinafter, referred to as a microcomputer 5) controls the entire AM receiver. The automatic tuning detection circuit 6 outputs whether or not to tune to the received signal based on the signal strength of the received signal.

In FIG. 6, a received signal applied to a high frequency amplifier circuit 1 is mixed with a local oscillation signal from a local oscillator circuit 4 by a mixer circuit 2, converted into an intermediate frequency signal, and transmitted to an intermediate frequency amplifier circuit 3. Is done. In the intermediate frequency amplification circuit 3, frequency information is output from the intermediate frequency signal output terminal 8 to the microcomputer 5, and signal strength information is transmitted from the signal strength output terminal 9 to the automatic tuning detection circuit 6. Automatic tuning detection circuit 6
Compares the reference voltage for automatic tuning sensitivity determination specified by the predetermined voltage E with the voltage of the signal strength information of the signal received from the signal strength output terminal 9. When the voltage of the signal strength information of the received signal from the signal strength output terminal 9 exceeds E, the automatic tuning detection circuit 6 sets the automatic tuning detection signal (hereinafter, referred to as SD) to Hi level, To send to. Also,
When the voltage of the signal strength information of the received signal from the signal strength output terminal 9 falls below E, the automatic tuning detection circuit 6
Is set to Lo level and sent to the microcomputer 5. Microcomputer 5
Instructs the high frequency amplifier circuit 1 and the local oscillation circuit 4 by SD from the automatic channel selection detection circuit 6. The microcomputer 5
A voltage is output to the a-line to adjust the tuning characteristics of the high-frequency amplifier circuit 1 to the tuning frequency, and at the same time, control the frequency of the local oscillation circuit 4 to a value corresponding to the tuning frequency. In addition, the microcomputer 5 controls so as to avoid saturation of the high-frequency amplifier circuit when the signal input to the high-frequency amplifier circuit of the selected frequency becomes extremely large by the b-line. Generally, the gain of the high-frequency amplifier circuit is reduced by reducing the DC voltage so that a stronger input can be tolerated.

Next, a method of automatic channel selection will be described. Assuming that an automatic tuning operation is performed during reception of 522 KHz, 531 KHz, 540 KHz, ..., 594 KH
A case will be described in which z is automatically selected, and the signal stops at 594 KHz due to a signal higher than the tuning sensitivity.

When an instruction to start automatic tuning is input to the microcomputer 5 by operating a switch or the like for starting automatic tuning, the voltage of the line a is changed to change the oscillation frequency of the local oscillation circuit from 972 kHz to 981 kHz. Let it. The microcomputer 5 minutely controls the a-line while monitoring the oscillation frequency, and maintains the accuracy of the oscillation frequency. This frequency accuracy is generally ensured by a PLL circuit in the microcomputer. The high-frequency amplifier circuit is set to 522 by the voltage of the line a.
The tuning point has shifted from KHz to 531 KHz. The output from the high-frequency amplifier circuit and the oscillation output from the local oscillator circuit are mixed by a mixer circuit, the frequency information is the frequency of two waves (450 KHz), and the signal strength information is the output signal from the high-frequency amplifier circuit. , And sends it to the intermediate frequency amplifier circuit. In the intermediate frequency amplifier circuit, 45
The signal of 0 KHz is amplified and detected, the frequency information is outputted from the intermediate frequency signal output terminal 8 to the microcomputer 5, and the DC output proportional to the signal strength is outputted as the signal strength information from the signal strength output terminal 9 to the automatic channel detecting circuit 6. Send out. When the signal strength information is smaller than a preset value, the automatic tuning detection circuit 6 keeps the output signal (SD) at Lo. If the SD signal is Lo, the microcomputer 5 controls the a-line to set the oscillation frequency of the local oscillation circuit 4 to 990 KHz, the tuning point of the high frequency amplification circuit to 540 KHz, and the output SD of the automatic channel selection detection circuit.
Is confirmed, and in the case of Lo, the a-line is further controlled. The above operation is repeated until the SD signal becomes Hi. When the oscillation frequency of the local oscillation circuit 4 is 1044 KHz and the tuning point of the high-frequency amplification circuit 1 is 594 KHz, the DC output from the intermediate frequency amplification circuit 3 to the automatic tuning detection circuit is higher than the value set in advance by the automatic tuning detection circuit. Is increased, the SD signal from the automatic channel selection detection circuit becomes Hi. Since the SD signal is Hi, the microcomputer determines that the station can be automatically selected and stops the selection.

[0006] In the AM receiver, for example, the automatic tuning frequency is set to the lower limit frequency (fL) 522 KH of the AM band.
The stability of the output from the signal strength output terminal 9 when changing from z to the upper limit frequency (fH) of 1629 KHz depends on the gain characteristics of the high frequency amplifier circuit 1 with respect to the frequency. As a result, the output of the SD also depends on the frequency characteristics of the high-frequency amplifier circuit 1. This will be described below with reference to FIG.

FIG. 5 is a circuit diagram of the high-frequency amplifier circuit 1 shown in FIG. As a high-frequency amplifier circuit, generally, H
Either a high-frequency amplifying circuit of the system or an I-type high-frequency amplifying circuit, or a circuit similar to either of them is often adopted. The H system is a selective amplifier, and I
The method is a flat amplifier having no selection characteristics such that the gain characteristics are not affected by frequency. The I method is shown in FIG.
As shown in (1), the signal from the FET Q3 is amplified in a wide band and sent to the mixer circuit 2 from the connection point between the resistor Ra and the transistor Q1. The frequency-gain characteristic in this case is
One example is an f-curve as shown in FIG.

[0008] In the H system, as shown in FIG.
The reception signal from TQ3 is given a frequency selection characteristic by coil T1 and variable capacitance diode Da and coil T2 and variable capacitance diode Db, and the amplified signal is transmitted from coil T2 to mixer circuit 2. In the H system, as shown in FIG. 2, when the frequency is tuned to the lower limit frequency (fL), the frequency characteristic from the FET Q3 to the output of the T2 becomes the characteristic of 7a, and the frequency (f
Frequency characteristic is 7b when tuned to the frequency of M)
When the frequency is tuned to the upper limit frequency (fH), the frequency characteristic becomes 7c. The overall frequency characteristic is an e-curve connecting the vertices of 7a, 7b and 7c. Further, the overall frequency characteristic is T
Depending on the characteristics of 1, T2, Da and Db, it becomes like an example of a d curve or a g curve as shown in FIG.
A large frequency deviation occurs. In the H system, the center point of the selection characteristics can be changed by the voltage of the a-line. fL ・ fM ・ fH
Is performed by voltage control of the a-line.

In FIG. 5, the signal lines b and c control the operating points of the transistors Q2 and Q1, respectively, so as not to transmit an excessive signal to the mixer circuit, and are controlled by the microcomputer 5. When,
In some cases, control is directly performed from the signal strength output terminal 9.

As the above-mentioned prior art, there is a technique disclosed in pages' 160-169 of "'91 -'92 Sanyo Semiconductor Data Book for Car Audio Integrated Circuit".

[0011]

As described above, when the high-frequency amplifier circuit is of the I-type, the channel selection sensitivity deviation with respect to the automatic channel selection frequency is small because it has no selection characteristics. There is a case where a channel is selected at a frequency of 1 time, 2 times, 3 times, or the like of ambient noise or a frequency difference between a plurality of broadcast station signals, thereby causing an error stop. Here, the erroneous stop is a channel selection error. In other words, instantaneous noise and the interaction of multiple strong broadcast signals create a situation in which a fictitious broadcast signal is present at a frequency at which there is no broadcast signal with the strength to stop originally, And the like. In particular, in the case of the I method, the occurrence is remarkable because there is no selection characteristic.

When the high-frequency amplifier circuit is of the H type, it is difficult to eliminate the frequency dependence while keeping the selection characteristics of the high-frequency amplifier circuit sharp. As shown in FIG. The frequency dependency as in the example of the curve and the g curve appears, and as a result, the tuning sensitivity deviation with respect to the automatic tuning frequency increases. That is, if the high-frequency amplifier circuit is a flat amplifier as in the I method, there is basically no channel selection sensitivity deviation. However, if the high-frequency amplifier circuit has a selection characteristic, a little at each frequency. There is a difference in gain. 522KHz for AM receiver
The difference between the maximum value and the minimum value of the gain between １６1620 KHz is expressed as a sensitivity deviation. As the direct cause of the sensitivity deviation, the difference between the characteristics of T1 and T2 and the characteristic values of Da and Db shown in FIG. In particular, Da and Db
Is provided in the same chip, and 2
Although the difference in characteristics has been greatly reduced compared to the era of chip construction, it is not entirely complete.

An object of the present invention is to provide a method and an apparatus for automatically selecting a receiver, which reduce erroneous stop and reduce deviation of tuning sensitivity.

[0014]

In order to solve the above-mentioned problems, as an amplifier circuit for receiving a signal and amplifying a received signal, a gain characteristic is different from a flat characteristic amplifier circuit whose gain characteristic is not affected by frequency. A selection characteristic amplifying circuit, an automatic tuning method in a receiving device for tuning a frequency of a received signal, wherein as a first step,
Amplify the received signal in the flat characteristic amplifier circuit,
A specific frequency component of the amplified received signal is extracted, and the presence or absence of a signal station is detected based on the extracted signal.
As a step, when there is the signal station, amplify the received signal in the selective characteristic amplifier circuit, and extract the signal of the specific frequency component of the amplified received signal,
Based on the extracted signal, the presence or absence of a signal station is detected, and if the signal station is present, it is determined as a channel selection. As a third step, in the first step and the second step, If there is no signal station, the frequency of the specific frequency component is sequentially changed, and the process proceeds to the first step.

The first step and the second step
The detection of the presence or absence of the signal station in the step (c) can be detected based on the signal strength of the extracted signal. The detection of the presence or absence of the signal station in the second step is performed when the signal strength detected in the second step is larger than a value obtained by subtracting a predetermined value from the signal strength detected in the first step. A station may be provided.

Further, in a receiving apparatus for receiving a signal, amplifying the received signal, and automatically selecting the received signal, a flat characteristic amplifying means for receiving the signal, amplifying the received signal, and having a gain characteristic not influenced by frequency. Receiving a signal, amplifying the received signal, a gain characteristic selection means having different gain characteristics depending on the frequency, an extracting means for extracting a specific frequency component of the amplified received signal, based on the extracted signal, A tuning unit that detects the presence or absence of a signal station; and a switching unit that switches amplification of a reception signal between the flat characteristic amplification unit and the selection characteristic amplification unit. The switching unit amplifies the signal in the flat characteristic amplification unit. And selecting the signal station by the tuning detecting means, and then switching the signal characteristic to amplifying by the selecting characteristic amplifying means. The channel selection detecting means may detect that a signal station exists when the signal strength of the extracted signal is equal to or higher than a predetermined signal strength.

When the signal station is detected by the channel selection detecting means, the signal strength S1 of the extracted signal is held, and after the switching of the switching means, the signal of the signal amplified and extracted by the selection characteristic amplifying means is output. It is possible to further include a comparison / determination means for holding the strength S2, comparing the signal strength S2 with a value obtained by subtracting a predetermined value from the signal strength S1, and selecting a station when the signal strength S2 is large.

[0018]

When there is an instruction to automatically select a channel, the switching means provided in the microcomputer selects the amplification by the flat characteristic amplification means, and the flat characteristic amplification means receives the signal and amplifies the received signal. The extracting means extracts a specific frequency component of the amplified received signal. The channel selection detecting means detects the presence or absence of a signal station based on the extracted signal. The switching means switches the signal to be amplified by the selection characteristic amplifying means after detection of the signal station by the channel selection detecting means. The comparing and judging means holds the signal strength S1 of the extracted signal at the time of detection of the signal station by the channel selection detecting means, and after the switching of the switching means, the signal amplified and extracted by the selection characteristic amplifying means. Is held, and a value obtained by subtracting a predetermined value from the signal strength S1 is compared with the signal strength S2. When the signal strength S2 is large, tuning is performed.

In the case where there is no signal station in the channel selection detecting means, and in the case where the signal strength S2 is not large as a result of comparison between the signal strength S2 and a value obtained by subtracting a predetermined value from the signal strength S1 in the comparison determining means. Changes a specific frequency of the amplified received signal extracted by the extracting means. For example, the specific frequency is increased by 9 kHz.

The presence / absence of a signal station in the channel selection detecting means is detected as the presence of a signal station when the signal strength of the extracted signal is equal to or higher than a predetermined signal strength. Alternatively, if the specific frequency component extracted by the extraction means is within a predetermined range, it may be determined that there is a signal station. Alternatively, a combination of these may be used when the signal strength of the extracted signal is equal to or higher than a predetermined signal strength and the specific frequency component extracted is within a predetermined range.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
A more detailed description will be given of a case in which an automatic tuning frequency is automatically selected from a lower frequency to a higher frequency in the M-band receiver.

FIG. 1 shows a block diagram in the present embodiment. FIG. 4 is a circuit diagram of the high-frequency amplifier circuit according to the present embodiment.

In FIG. 1, an antenna 13 receives a signal. The high-frequency amplifier circuit 10 includes H-type and I-type high-frequency amplifier circuits. The signal line b1 and the c1 line are alternately controlled to switch between the H-type and the I-type. Amplify the signal. FET Q3,
From the coil T2 to the mixer circuit 2, the signal from the FET Q3 is given a selection characteristic by the coil T1 and the variable capacitance diode Da, and the coil T2 and the variable capacitance diode Db, and the signal from the FET Q3 is provided. There is an H-type high-frequency amplifier circuit for transmitting an amplified signal. Local oscillation circuit 4 oscillates at the designated local oscillation frequency. Mixer circuit 20
Converts the local oscillation signal from the local oscillation circuit 4 and the amplified received signal to output an intermediate frequency signal. The intermediate frequency amplifier circuit 30 amplifies the intermediate frequency signal from the mixer circuit 20, outputs frequency information from the intermediate frequency signal output terminal 8, and outputs signal strength information from the signal strength output terminal 9. Microcomputer 50 (hereinafter, microcomputer 50)
) Controls the entire AM receiver. Further, the mixer circuit 20, the local oscillator circuit 4, and the intermediate frequency amplifier circuit 30 function as an extracting unit that extracts a specific frequency component of the received signal amplified by the high frequency amplifier circuit 10. Further, the extracting means may include the microcomputer 50. The automatic tuning detection circuit 6 outputs whether or not to tune to the received signal based on the signal strength of the received signal. Input unit 51
Receives at least an automatic tuning start instruction. The demodulation unit 52 demodulates and outputs the intermediate frequency reception signal amplified by the intermediate frequency amplification circuit 30. In FIG. 1, the connection from the high-frequency amplifier circuit 10 to the mixer circuit 20, the connection from the signal strength output terminal 9 to the microcomputer 50, and the connection from the microcomputer 50 to the high-frequency amplifier circuit 10 are the same as those of the conventional AM shown in FIG. It differs from the block diagram of the receiver. The microcomputer 50 controls the frequency of the local oscillation circuit to a value corresponding to the selected frequency while outputting the voltage via the a1 line to adjust the tuning characteristic of the high-frequency amplifier circuit to the selected frequency. Further, the microcomputer 50 alternately controls the b1 line and the c1 line and uses them for switching between the H system and the I system. Further, both the b1 line and the c1 line are controlled so as to avoid saturation of the high frequency amplifier circuit when the channel selection signal or the signal input to the high frequency amplifier circuit becomes extremely large. Generally, by reducing the DC voltage, the gain of the high-frequency amplifier circuit is reduced,
Be able to withstand stronger input. As another example, there is a case where a plurality of automatic channel selection sensitivities are set by using a plurality of DC voltage values. Further, as another example, by setting the DC voltage value to a very small value, it is possible to treat the high-frequency amplifier circuit as a function stop state without cutting off the power supply or the like.

Next, the receiving operation in the AM receiver and the processing operation of automatic channel selection will be described with reference to FIGS. FIG. 3 shows a processing flow of automatic channel selection.

When the input section 51 receives an instruction to start automatic tuning, the microcomputer 50 starts automatic tuning according to a processing flow as shown in FIG. As a trigger for starting the automatic tuning, the microcomputer 50 monitors the signal strength instead of the automatic tuning start instruction in the input unit 51, and
Automatic tuning may be started when the signal strength becomes weaker than a predetermined signal strength. As another example, when an automatic tuning start instruction is received, a reception signal may be output for a fixed time after the automatic tuning, and the automatic tuning may be started again after a certain time has elapsed. In this case, the user of the receiver listens to the received signal for a certain period of time while automatically selecting a station, and can specify the receiving station when the station has the desired content.

As described above, when the automatic channel selection is started (step 100), the microcomputer 50 sets the line b1 to Lo to turn off the transistor Q2, and sets the line c1 to Hi to turn on the transistor Q1 (step 101). The switching control by the transistor is used as a switching unit, and the switching unit can switch the I-type amplifier so as not to operate the H-type amplifier.

The reception signal from the reception antenna 13 is input to the FET Q3, and the FET Q3 and the transistor Q1
And an I-type amplifier circuit including a resistor Ra, the received signal is amplified and output. The amplified received signal is sent to the mixer circuit 20 from the intersection of the resistor Ra and the transistor Q1. At this time, the gain characteristic with respect to the reception frequency approximates the f-curve shown in FIG. Since the I method is a flat amplifier that has no selection characteristics,
The gain is almost constant at any frequency. Also, b
Since one line is Lo, the H type amplifying circuit composed of T1, T2, Da and Db is in a quiescent state.

Next, the microcomputer 50 controls the oscillation frequency of the local oscillation circuit to a value (hereinafter, referred to as F) corresponding to the automatic tuning frequency by a DC voltage via the a1 line (step 102), and Instruct to set to plus 9 KHz. F increases the frequency by 9 KHz with respect to the reception frequency selected earlier. For example, 522K
Hz, 531KHz, 540KH
.., 594 KHz. This 9 KHz is a value specified by the broadcasting station frequency interval in Japan. Since it is not necessary for the receiver to select a 9 KHz step at the time of channel selection, when a special function or operation is required, a value other than 9 KHz may be set. For a receiver used in the United States, the frequency is set to +10 KHz. The local oscillation circuit is a voltage-controlled oscillator that changes the frequency by voltage control, and the frequency is controlled based on the DC voltage via the a1 line. The output from the high-frequency amplifier circuit 10 and the oscillation output from the local oscillation circuit 4 are mixed by a mixer circuit 20, and the frequency information is a frequency of a difference between two waves.
The signal strength information is converted into a signal proportional to the output signal from the high frequency amplifier circuit 10 and sent to the intermediate frequency amplifier circuit 30. The intermediate frequency amplifier circuit 30 amplifies and detects the received signal, outputs frequency information from the intermediate frequency signal output terminal 8 to the microcomputer 50, and automatically outputs a DC output proportional to the signal intensity from the signal intensity output terminal 9 as signal intensity information. Tuning detection circuit 6
Send to The automatic tuning detection circuit 6 compares the signal strength information with a preset value. When the signal strength information is smaller than the preset value, the output signal (hereinafter, referred to as SD signal) is set to Lo, and the signal strength information is set to Lo. If the value is equal to or greater than a preset value, the SD signal is set to Hi.

The microcomputer 50 checks the SD signal from the automatic channel selection detection circuit 6 (step 103). If the SD signal is not Hi, the microcomputer 50 determines that there is no condition for stopping the automatic channel selection, returns to step 102, and further sets F. Add 9 KHz. When the SD signal from the automatic channel selection detection circuit 6 is Hi, the microcomputer 50 measures the frequency of the intermediate frequency signal from the intermediate frequency signal output terminal 8 (step 104), and obtains a predetermined value of 450K.
If the frequency is other than Hz ± 3 KHz, it is determined that there is no condition for stopping the automatic tuning, and the processing is executed again from step 102. Also,
The frequency of the intermediate frequency signal from the intermediate frequency signal output terminal 8 is measured, and if it is within a predetermined value range of 450 KHz ± 3 KHz, automatic channel selection can be stopped and the frequency is temporarily captured.
The microcomputer 50 outputs the signal strength S1 from the signal strength output terminal 9.
Is measured, and the signal strength S1 is held (step 10).
5). This predetermined value of 450 KHz can be set at another frequency. Depending on the circuit configuration of the receiver, 225 KHz or 46 KHz may be used.
It may be 0 KHz. When a general-purpose element is used, 450 KHz is desirable.

Next, the microcomputer 50 sets the b1 line to Hi, turns on Q2, and sets the c1 line to L
Q1 is turned off as o (step 106). As a result, it is possible to switch so as not to operate the I-type amplifier and to operate the H-type amplifier. In the H type amplifying circuit, the received signal from the receiving antenna is
3 and a tuning circuit composed of a coil T1 and a variable capacitance diode Da, and a tuning circuit composed of a variable capacitance diode Db and a coil T2, via a FET Q3 and a transistor Q2, to set the central point of the selection characteristic. The signal varies with the voltage of the a1 line, amplifies the received signal, and sends it to the mixer circuit 20. At this time, the gain characteristic of the reception frequency with respect to the frequency up to the mixer circuit 20 can be various, as shown in FIG. 2, such as a d, e, or g curve. In the following description, a case where the tuning is performed so as to indicate the gain characteristic of the e-curve will be described unless otherwise specified. After the mixer circuit 20, reception processing is performed in the same manner as described above. In this case, the oscillation frequency of the local oscillation circuit 4 is the oscillation frequency captured in step 103 when the SD signal is Hi.

Next, as in step 104, the microcomputer 50 measures the frequency of the intermediate frequency signal from the intermediate frequency signal output terminal 8 (step 107) and obtains a predetermined value of 450K.
If the frequency is other than Hz ± 3 KHz, it is determined that there is no condition for stopping the automatic tuning, and the processing is executed again from step 102. If the predetermined value is within the range of 450 KHz ± 3 KHz, the signal strength S2 is measured from the signal strength output terminal 9, and the signal strength S2 is held (step 108).

The signal strength S1 held in step 105 is equal to the reception frequency f when the f characteristic shown in FIG.
Assuming that L, it is measured by the gain of G at the intersection of fL and f-curve. The signal strength S2 held in step 108 is measured by the gain of GL at the intersection of fL and the e-curve, assuming that the reception frequency is fL in the case of the e characteristic shown in FIG. Therefore, a difference K between G and GL exists between S1 and S2. Next, the microcomputer 50 determines whether or not the following equation 1 is satisfied (step 1).
09). If Equation 1 is not satisfied, the determination is No, and the processing is re-executed from Step 102. If Equation 1 is satisfied, the automatic tuning condition is finally satisfied, and the determination is Yes and the automatic tuning is stopped (Step 110). .

[0033]

## EQU1 ## As an example in which Equation 1 does not hold, the influence of ambient noise is considered. In such a case, automatic tuning is not performed. That is, since the selection characteristics of the I-system high-frequency amplifier circuit 10 are gradual, due to ambient noise, automatic selection is automatically performed at a frequency that the user does not want to automatically stop tuning, and when the amplification circuit is switched to the H system and amplified, Due to the sharp selection characteristic of the H-system high-frequency amplifier circuit 10, the level of the ambient noise has been greatly reduced, so that Equation 1 does not hold. By making such a determination, it is possible to avoid erroneous stoppage of automatic channel selection.

In steps 101 to 105, the signal can be captured without the automatic tuning sensitivity deviation by detecting the SD by making the selection characteristics of the amplifier circuit flat and detecting the SD. However, since the selection characteristics are flat, for example, Even at frequencies where there is no actual broadcast station, such as ambient noise, twice the broadcast frequency, or once, twice, or three times the frequency difference between broadcast stations, the signal stops erroneously, and the signal stops. A signal having a sufficient strength is also output to the strength output terminal 9. On the other hand,
In steps 106 to 108 described above, a large sensitivity deviation appears to sharpen the selection characteristics of the amplifier circuit.
Because of the sharp selection characteristics, ambient noise, twice the frequency of the broadcast frequency, or 1 time, 2 times, 3 times the frequency difference between broadcast stations
At frequencies where no broadcasting station actually exists, such as twice the frequency, a remarkable rejection capability appears.
Only a very small signal appears. Therefore, in Steps 101 to 105, all frequency points exceeding the automatic tuning sensitivity are detected, and the amplifier circuit is switched to select the frequency points in Steps 106 to 109, thereby keeping the automatic tuning sensitivity deviation small. However, the number of automatically selected stations can be properly controlled.

As described above, by using an amplifier circuit that is not affected by frequency, a signal is captured, and furthermore,
By using an amplifier circuit having a sharp selection characteristic that affects the frequency, erroneous stop can be prevented.

This embodiment is merely an example, and various modifications and improvements can be made without departing from the scope of the present invention.

As described above, according to this embodiment, H
A system and an I-system amplifying circuit are provided, which is selected and captured by the I-system amplifying circuit, switched to an H-system amplifying circuit, and determined based on the signal strength, thereby preventing erroneous stop of automatic tuning. be able to. Further, the automatic tuning sensitivity deviation can be reduced.

[0038]

According to the present invention, it is possible to reduce an erroneous stop and a deviation in tuning sensitivity.

[Brief description of the drawings]

FIG. 1 is a block diagram for performing automatic channel selection in an embodiment.

FIG. 2 shows a frequency characteristic of a high-frequency amplifier circuit in the embodiment.

FIG. 3 is a flowchart of a microcomputer in the embodiment.

FIG. 4 is a high-frequency amplifier circuit according to the embodiment.

FIG. 5 is a conventional high-frequency amplifier circuit.

FIG. 6 is a block diagram of a conventional AM receiver.

[Explanation of symbols]

1 and 10: High frequency amplifier circuit, 2 and 20: Mixer circuit, 3 and 30: Intermediate frequency amplifier circuit, 4: Local oscillation circuit, 5 and 50: Microcomputer, 6: Automatic channel selection detection circuit, 7a, 7b, 7c Tuning waveform, 8 ... Intermediate frequency signal output terminal, 9 ... Signal strength output terminal, a and a1 ... Tuning voltage signal line, bc and b1c1 ... Selection characteristic switching signal line, deefg ... frequency Characteristic curve, fL ... AM
The lower limit frequency of the band (522 KHz), fM ... frequency near the center of the AM band, fH ... the upper limit frequency of the AM band (1629 KHz), E ...
Automatic tuning sensitivity determination reference voltage.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-145339 (JP, A) JP-A-3-15809 (JP, A) JP-A-3-160824 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H03J 7/18 H04B 1/16-1/26

Claims (4)

(57) [Claims] 1. A receiving device for automatically selecting a signal station, wherein a gain of a received signal is not affected by frequency.
Flat characteristic amplifier and amplifies received signal, gain characteristics differ depending on frequency
Selection characteristic amplifying means for extracting a specific frequency component of the amplified received signal;
Extraction means, and the signal strength of the extracted signal extracted by the extraction means is
Detection means for detecting that the signal strength is equal to or higher than a predetermined signal strength, and at the start of automatic channel selection, the flat characteristic amplification means is used.
Amplifying the received signal, and detecting means for extracting the signal strength of the extracted signal.
Detecting that the degree is equal to or higher than a predetermined signal strength,
Increase to amplify the received signal using the selection characteristic amplifier.
Switching means for switching width means, and signal strength of an extracted signal when the selection characteristic amplifying means is used.
Channel selection means for determining the presence or absence of a signal station based on the degree
A receiving device, comprising: 2. A receiving apparatus for automatically selecting a signal station , wherein the gain characteristic is not influenced by frequency, wherein the gain characteristic is amplified.
Flat characteristic amplifier and amplifies received signal, gain characteristics differ depending on frequency
Selection characteristic amplifying means for extracting a specific frequency component of the amplified received signal;
Extraction means, and the signal strength of the extracted signal extracted by the extraction means is
Detection means for detecting that the signal strength is equal to or higher than a predetermined signal strength, and at the start of automatic channel selection, the flat characteristic amplification means is used.
Amplifying the received signal, and detecting means for extracting the signal strength of the extracted signal.
Detecting that the degree is equal to or higher than a predetermined signal strength,
Increase to amplify the received signal using the selection characteristic amplifier.
Switching means for switching the width means, and the detecting means makes the signal strength of the extracted signal equal to or less than a predetermined signal strength.
Signal strength S1 of the extracted signal when it is detected that the
It holds, after the switching means has switch the amplifying means
Is greater than the value of the signal strength S1.
Is larger than the predetermined value, the signal station related to the extracted signal is
Receiving means for selecting a station.
Place. 3. A method for amplifying a received signal, comprising:
Extracts specific frequency components and outputs the extracted signals.
Automatic tuning method that detects the presence or absence of a signal station based on signal strength
The gain characteristic is not affected by frequency at the start of automatic tuning
Amplify and identify received signal using flat characteristic amplifier
The signal strength of the signal extracted for the frequency components of
If the signal strength is higher than the
Amplify the received signal by switching to a selection characteristic amplifying means,
Signal strength of a signal extracted for the specific frequency component
Characterized in that the presence or absence of a signal station is determined based on the degree
Automatic tuning method. 4. Amplifying a received signal, and amplifying the amplified received signal.
Extracts specific frequency components and outputs the extracted signals.
Automatically selects a signal station based on signal strength
Stomach, at the time of automatic tuning start, gain characteristics are not affected by the frequency
Amplify and identify received signal using flat characteristic amplifier
The signal strength of the signal extracted for the frequency components of
If the signal strength is higher than the
Amplify the received signal by switching to the selected characteristic amplifying means, when using the selective characteristic amplifying means, a specific frequency component
The signal strength of the signal extracted for
Extraction of specific frequency components when
If the signal strength is greater than the signal strength of the
Selecting a signal station related to the extracted signal.
Automatic tuning method.