JP3213088B2 - 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 amplifying circuit is of the I-type, since there is no selection characteristic, the tuning sensitivity deviation with respect to the automatic tuning frequency is small. When there is a signal and the signal strength of some input signals is very large, saturation occurs due to excessive input in the mixer circuit. To avoid this, an AGC circuit for controlling the gain based on the signal strength of the received signal is provided, and the AGC circuit limits the gain of the amplifier circuit. As a result, a signal having a small signal strength is suppressed and becomes lower than a level that can be captured by automatic channel selection. If the signal strength of a desired station is low, automatic channel selection cannot be performed.

On the other hand, when the high-frequency amplifier circuit is of the H type, since the selection characteristics are sharp, there are a plurality of input signals, and even when the signal strength of some of the input signals is very high, the signal strength is low. By tuning to, a signal having a large signal strength can be eliminated, and automatic tuning can be performed even when the signal strength of a desired station is low.

However, when the high-frequency amplifier circuit is of the H type, frequency selection characteristics such as those of the d-curve, e-curve, and g-curve shown in FIG. 2 appear.
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 tuning sensitivity deviation,
When the high-frequency amplifier circuit has a selection characteristic, the gain is slightly different at each frequency. In the case of an AM receiver, the difference between the maximum value and the minimum value of the gain between 522 KHz to 1620 KHz is expressed as a sensitivity deviation.
The direct cause of the sensitivity deviation is the T
Mainly is the difference between the characteristics of 1 and T2, and the characteristic values of Da and Db. In particular, Da and Db are provided in the same chip, and the difference in characteristics is greatly reduced as compared with the past when two chips were used, but they are not completely complete.

An object of the present invention is to reduce a tuning sensitivity deviation,
An object of the present invention is to provide a method and an apparatus for automatically selecting a receiver that can secure stable tuning sensitivity.

[0015]

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. An automatic tuning method in a receiving device that includes a selection characteristic amplification circuit and tunes a frequency of a reception signal, wherein the flat characteristic amplification circuit and the selection characteristic amplification circuit are switched based on the signal strength of the reception signal. Extracting a specific frequency component of the received signal amplified by the switched amplifier circuit, detecting the presence or absence of a signal station based on the extracted signal, selecting a signal station if there is one, and selecting no signal station. In this case, the frequency of the specific frequency component is sequentially changed.

The switching between the flat characteristic amplification circuit and the selection characteristic amplification circuit is switched to the selection characteristic amplification circuit when the signal strength of the received signal is equal to or more than a predetermined value, and the signal strength of the reception signal is set to a predetermined value. When the value is smaller than the value, the circuit is switched to the flat characteristic amplifier circuit.

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. A selection characteristic amplifying means for receiving a signal, amplifying a received signal, and having different gain characteristics depending on frequency; an extracting means for extracting a specific frequency component of the amplified received signal; and a signal based on the extracted signal. It can include a channel selection detecting means for detecting the presence or absence of a station, and an AGC circuit for controlling a gain based on the signal strength of a received signal.

The apparatus further comprises switching means for switching the amplification of the reception signal between the flat characteristic amplification means and the selection characteristic amplification means, wherein the AGC circuit detects the signal strength of the reception signal, and wherein the switching means comprises: The switching between the flat characteristic amplifying circuit and the selective characteristic amplifying circuit can be performed based on the signal strength of the received signal detected in the step (a).

The AGC circuit further detects whether the signal strength of the received signal is equal to or more than a predetermined value,
The switching unit switches to the selective characteristic amplifier circuit when the signal strength of the received signal is equal to or higher than a predetermined value, and switches to the flat characteristic amplifier circuit when the signal intensity of the received signal is not equal to or higher than the predetermined value.

[0020]

The AGC circuit controls the gain based on the signal strength of the received signal and detects the signal strength of the received signal. The switching means switches between the flat characteristic amplifier circuit and the selective characteristic amplifier circuit based on the signal strength of the received signal detected by the AGC circuit. The switching means switches to the selective characteristic amplifier circuit when the signal strength of the received signal is equal to or higher than a predetermined value. The selection characteristic amplifier circuit receives the signal, amplifies the received signal, and the extracting unit 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, and selects a channel when there is a signal station. If there is no signal station, the frequency of the specific frequency component in the extracting means is changed. For example, the specific frequency is increased by 9 kHz.

The switching means switches to the flat characteristic amplifier circuit when the signal strength of the received signal is not higher than a predetermined value. In the flat characteristic amplifier circuit, receives a signal, amplifies the received signal, the extraction means,
A specific frequency component of the amplified received signal is extracted.
The channel selection detecting means detects the presence or absence of a signal station based on the extracted signal, and selects a channel when there is a signal station. If there is no signal station, the frequency of the specific frequency component in the extracting means is changed.

[0022]

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. 5 is a circuit diagram of the high-frequency amplifier circuit according to the present embodiment.

In FIG. 1, an antenna 13 receives a signal. Broadband AGC (Automatic Gain Control) circuit 1
1 controls the amplitude of the signal according to the strength of the radio wave.
Further, the wideband AGC circuit 11 includes a detecting unit for detecting that the intensity of the radio wave is equal to or higher than a predetermined electric field intensity Ea,
The switching element 12 is operated according to the detection result, and the detection result is output. 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, transistor Q1 and resistor Ra
A radio frequency amplifier circuit of the I type comprising, FET Q3 and tiger
An H-type high-frequency amplifier circuit for providing a signal from the transistor Q2 with selection characteristics of the coil T1 and the variable capacitance diode Da and the coil T2 and the variable capacitance diode Db, and transmitting an amplified signal from the coil T2 to the mixer circuit 2 is provided. is there. Local oscillation circuit 4 oscillates at the designated local oscillation frequency. The mixer circuit 20 modulates the local oscillation signal from the local oscillation circuit 4 and the amplified reception signal to output an intermediate frequency signal. Intermediate frequency amplifier circuit 30
Amplifies the intermediate frequency signal from the mixer circuit 20,
Frequency information is output from an intermediate frequency signal output terminal 8 and signal strength information is output from a signal strength output terminal 9. The microcomputer 50 (hereinafter referred to as the microcomputer 50)
It controls the entire M receiver. Also, the mixer circuit 20,
The local oscillation circuit 4 and the intermediate frequency amplification circuit 30 function as extraction means for extracting a specific frequency component of the reception signal amplified by the high frequency amplification 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. The 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. The control by the microcomputer 50 is as follows.
A voltage is output via the a1 line to adjust the tuning characteristics of the high-frequency amplifier circuit to the tuning frequency and, at the same time, control the frequency of the local oscillation circuit to a value corresponding to the tuning 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. Furthermore, the b1 line and c1
The line is 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, the gain of the high-frequency amplifier circuit is reduced by reducing the DC voltage so that a stronger input can be tolerated. 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. The AGC circuit 11 controls the signal amplitude so that the signal level after modulation can be detected without change even if the intensity of the radio wave changes. As the AGC circuit, there are a plurality of techniques such as a circuit for controlling an intermediate frequency amplifier circuit and a circuit for controlling a high frequency amplifier circuit.
ICs described on page 164 of "'91 -'92 Sanyo Semiconductor Data Book Integrated Circuit for Car Audio"
A WIDE AGC as shown at pin 3 can be used. In the known example, 0.022u connected to the 3rd pin
The magnitude of the input signal is detected by the capacitor of F, and IC
510Ω as DC output from pin 3 after amplification and rectification inside
By passing a current through the diode through the resistor, the diode is gradually lowered to a low resistance state, and a signal up to the gate of the FET is bypassed to the ground side to prevent an excessive signal from being input to the FET gate. At the same time, the base voltage of the transistor connected to the FET as the RF AGC from the IC pin 1 is reduced to lower the gain of the high-frequency amplifier circuit, and control is performed so that the circuit is not saturated even if an excessive signal is input. In the present embodiment, the magnitude of the signal is detected from the connection point between Rb and Ra, and the gain is controlled via the line c1 so that the electric field does not exceed a predetermined electric field intensity. At the same time, the Q4 transistor 12 is turned on when the magnitude of the signal exceeds a specified value. Based on the state of the transistor, the microcomputer 50 can recognize that the signal has reached a specified value or more.

Next, the receiving operation in the AM receiver and the operation of the AGC circuit will be described with reference to FIGS. FIGS. 4A and 4B show broadcast electric field strength graphs, and FIGS. 4C and 4D show electric field strength graphs of input signals of the mixer circuit 12. In FIG. 4, it is assumed that a broadcast station signal exists at the frequency fD and the frequency fUD, and a case where the apparatus as shown in FIG. 1 captures a broadcast station signal having an electric field strength S or more by automatic channel selection will be described. . In this embodiment, the microcomputer circuit 5 controls the AGC circuit so that the electric field intensity does not exceed Ea.
The amplifier circuit is switched by 0.

When a broadcast station signal having a broadcast electric field strength S or higher as shown in FIG. 4A is captured by automatic tuning, the microcomputer 50 shown in FIG. 1 connects the base of the transistor Q2 to the b1 line. It is set to Lo, and the base of the transistor Q1 is set to Hi via the c1 line. The signal received from the antenna 10 is amplified by the FET Q3 of the I-type high-frequency amplifier circuit and connected to the wideband AGC circuit 11 from the connection point between the resistor Ra, the coil T1, and the resistor Rb, and at the same time, the resistor Ra and the transistor Q1 are connected. Is input to the mixer circuit 20 from the connection point with the. Broadband AGC circuit 11
A signal is input from the connection point between the resistors Rb and Ra, and the detection means detects that the electric field strength of this signal is equal to or higher than Ea shown in FIG. Is turned on. Further, the wideband AGC circuit 11 lowers the base voltage of the transistor Q1 via the line c1 and limits the input to the mixer circuit 20 so as not to increase. In FIG. 4, the electric field strength Ea is represented by a resistance Ra
From the connection point of the transistor Q1 and the mixer circuit 20
The signal input to the mixer circuit 20 is set to a value lower than the value that causes excessive input in the mixer circuit 20. Generally, a value about 20 to 50 dBu lower than the electric field strength near the AM broadcasting station is set.

The signal input to the mixer circuit 20 is mixed with the oscillation signal of the local oscillation circuit 4 controlled by the microcomputer 50 via the line a1 in the mixer circuit 20, and then mixed as an intermediate frequency signal into the intermediate frequency amplifier circuit 30. Sent out. 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 channel selection detection circuit 6 generates signal strength information E
(E is equal to the signal strength information of the intermediate frequency amplifier circuit 30 when the electric field strength signal S is received as shown in FIG. 4). When the signal strength information is smaller than the preset E, the output signal (hereinafter, referred to as SD signal) is set to Lo. When the signal strength information is equal to or greater than the preset E, the SD signal is changed. Set to Hi.

In the above case, since the amplifying circuit uses the I system, the frequency characteristic becomes flat like the f-curve shown in FIG. 2, and both the frequency fD and the frequency fUD are equal to or higher than the electric field intensity S and equal to or lower than Ea. So switching element 1
2 is a range where it does not turn on and is captured by automatic channel selection.

In the case of the graph of the antenna input signal as shown in FIG.
Greatly exceeds the point Ea at which the operation starts, the gain is limited so that the frequency fUD signal becomes the Ea level. Similarly, the gain of the fD signal is limited, so that the strength cannot exceed S and cannot be captured by automatic channel selection. FIG. 4 shows a state before the gain is limited in this case.
(B). When the gain is limited in the AGC circuit 11, the antenna input signal as shown in FIG.
A graph as shown in (c) is obtained, and a signal of such an electric field strength becomes a mixer circuit input signal. At this time, the AGC circuit 11 sets the Q4
Is turned on.

Even in the input state of the graph as shown in FIG. 4B, the microcomputer sets the b1 line to Hi and the c1 line to Lo according to the result of Q4 of the switching element 12, and selects the high-frequency amplifier circuit. Switch to the H method. The switching control by the transistor is used as a switching unit, and the switching unit can be switched to operate the H system without operating the I-system amplifier. When the selection characteristic is tuned to be tuned to the frequency fD by the H-type amplifier circuit, the selection characteristic becomes 7d shown in FIG. 4D, whereby the signal of the frequency fUD is greatly weakened. The signal of the frequency fD is maintained at a level equivalent to the electric field strength as shown in FIG.
Input to 0. FIG. 4D shows the electric field strength characteristics of the input signal to the mixer circuit 20 in this case. In FIG. 4D, since the electric field strength exceeds S, it can be captured by automatic channel selection.

Next, the reception operation in the AM receiver will be described with reference to FIGS. 1 and 3 together with the processing operation of automatic channel selection. FIG. 3 shows a processing flow of automatic channel selection.

When an instruction to start automatic tuning is received at the input unit 51, the microcomputer 50 starts automatic tuning according to the processing flow shown in FIG. As a trigger for starting automatic tuning, instead of the automatic tuning start instruction in the input unit 51, the microcomputer monitors the signal strength, and when the signal strength becomes weaker than a predetermined signal strength, the automatic tuning is started. You may make it start. 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 tuning is started (step 100), the microcomputer 50 sets the switching element Q
The state of No. 4 is confirmed (step 101), and when the switching element Q4 is OFF, the transistor Q2 is turned off by setting the b1 line to Lo, and the transistor Q1 is turned on by setting the c1 line to Hi (step 102). When the switching element Q4 is ON, the transistor Q2 is turned on by setting the line b1 to Hi, and the transistor Q1 is turned off by setting the line c1 to Lo (Step 107).

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, and sets F to plus 9 KHz. (Step 10
3). 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 varies the frequency by voltage control, and the frequency is controlled based on a DC voltage via an oscillation frequency a1 line. High frequency amplifier circuit 1
The output from 0 and the oscillation output from the local oscillation circuit 4 are mixed by the mixer circuit 20, the frequency information is a frequency of a difference between two waves, and the signal strength information is proportional to the output signal from the high frequency amplification circuit 10. The signal is then transmitted to the intermediate frequency amplifier circuit 30 as an intermediate frequency signal. 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. The signal is sent to the channel selection detection circuit 6. 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
i.

The microcomputer 50 confirms the SD signal from the automatic channel selection detecting circuit 6 (step 104). 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 103, and further sets F. Add 9 KHz. When the SD signal from the automatic tuning 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 105), 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 103. 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 stopped at that frequency (step 106). This predetermined value of 450 KHz is also possible at other frequencies, and is 225 KH depending on the circuit configuration of the receiver.
z or 460 KHz. When a general-purpose element is used, 450 KHz is desirable.

In step 101, when the switching element Q4 is ON, the transistor Q2 is turned on by setting the line b1 to Hi, and the transistor Q1 is turned off by setting the line c1 to Lo (step 107). 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 connected to FET Q3
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 the FET Q3 and the transistor Q2. The signal varies depending on the line voltage, and the received signal is amplified and sent 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. After the mixer circuit 20, reception processing is performed in the same manner as described above.

In step 102, the selection characteristic of the amplifier circuit is made flat, and SD is detected.
Signal can be captured without automatic tuning sensitivity deviation. In this case, if the broadband AGC circuit 11 is provided, the gain is controlled. When the electric field strength of the received signal is higher than the predetermined electric field strength Ea, the gain is controlled in accordance with the electric field strength. At the same time, the electric field intensity Ea
The difference is detected by the detecting means, and the result is output. According to this result, the switching means of the microcomputer circuit 50 can switch to an H-type amplifier circuit having selection characteristics when the electric field strength Ea is larger.

As described above, when an amplifier circuit whose gain characteristic is not affected by frequency is used, a wideband AG
The electric field intensity is controlled by the C circuit in accordance with the signal having a strong signal intensity. However, when the electric field intensity is equal to or higher than a predetermined electric field intensity, an amplifier circuit having a sharp selection characteristic such that the gain characteristic affects the frequency is used. It can be selectively amplified. For example, when a signal of a frequency fUD having a large electric field strength that is not desired to be selected as a broadcasting station is input, and only the method I is used, when the frequency fD actually desired to be selected as a broadcasting station has a small electric field strength, a wideband AGC circuit is used. Since the electric field intensity is controlled in accordance with the signal having a high signal intensity, the signal of the frequency fD becomes smaller than the electric field intensity S, and the automatic tuning cannot be performed. In this embodiment, in such a case,
Since the signal is amplified by switching to the H method, if the selection characteristics of the coil T1 and the variable capacitance diode Da and the coil T2 and the variable capacitance diode Db are tuned to the frequency fD, the signal of the frequency fUD can be sufficiently eliminated.

The present 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 stable channel selection sensitivity can be secured by switching between the I-type amplifier circuit and the H-type amplifier circuit according to the electric field strength of the received signal.

[0042]

According to the present invention, the tuning sensitivity deviation can be reduced and a stable tuning sensitivity can be secured.

[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 shows frequency-electric field strength characteristics.

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 (2)

(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;
Extracting means, and a signal based on the extracted signal extracted by the extracting means.
Channel selection detecting means for detecting the presence or absence of a station; detecting the signal strength of the received signal; and detecting the signal strength based on the detected signal strength.
An AGC circuit for controlling the gain, and a signal intensity detected by the AGC circuit is equal to or higher than a predetermined value.
Sometimes, the received signal is increased by using the selective characteristic amplifying means.
Width, otherwise the flat characteristic amplifying means
Switch the amplifying means to amplify the received signal using
And a switching unit. 2. A method for amplifying a received signal, comprising:
Extracts a specific frequency component, and based on the extracted signal
Then, in the automatic channel selection method for selecting a signal station, when the signal strength of the received signal is equal to or higher than a predetermined value,
By using the selection characteristic amplification means whose gain characteristics differ depending on the number
Amplifies the received signal, otherwise the gain characteristics
Received using flat characteristic amplifier that is not affected by wave number
An automatic channel selection method characterized by amplifying a signal.