JP3486443B2 - AM radio receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AM radio receiver, and more particularly to improvement of tuning system.

[0002]

2. Description of the Related Art As an AM radio receiver in which tracking error is eliminated, for example, Japanese Patent Laid-Open No. 3-14533.
There is one disclosed in No. 9. This AM radio receiver tries to obtain accurate tuning by tuning using a coarse tuning signal and a fine tuning signal, and the tuning frequency of the RF tuning circuit when the tuning state of the receiver is fixed. Is finely controlled by the fine adjustment circuit. The principle of this fine tuning control is to change the tuning frequency, and at that time, the tuning frequency at which the S meter output (electric field strength signal) becomes the maximum is the best reception state.

An AM radio receiver of this type is disclosed in Japanese Patent Laid-Open No. 3-158016. This receiver is provided with a maximum value discriminating circuit, which compares the magnitude of the digital signal stored at address N of the memory with the digital signal stored at address N + 1 of the memory. Then, the address M of the memory in which the maximum digital signal is stored is determined by the procedure of comparing the large digital signal among them with the digital signal of the address N + 2. After that, a digital signal corresponding to the address M of the memory is selected and a fine adjustment signal is generated from the fine adjustment circuit so that the tuning frequency of the RF tuning circuit becomes an optimum value.

[0004]

However, the AM radio receiver adopting the conventional tuning method described above has the following problems.

First, the former AM radio receiver disclosed in Japanese Patent Laid-Open No. 3-145339 cannot obtain accurate tuning under the following conditions. (A) When the S meter output is saturated. When fine tuning control is performed when the S meter output having an electric field strength of B or more in FIG. 6 is saturated, an extremely wide band tuning characteristic as shown in A of FIG. 7 is obtained and an accurate tuning frequency can be obtained. Can not. This is generally known as a phenomenon that occurs when the S meter output is saturated and the AGC circuits in the RF and IF stages are fully working. (B) Deviation of tuning frequency due to temperature. In the circuit shown in FIG. 1, the tuning frequency is determined by the resonance frequency of the tuning circuit 17. Since the temperature coefficient of parts such as a capacitor, a varicap, and a coil that constitute this tuning circuit is different, the resonance frequency is shifted depending on the temperature. This means that exact tuning cannot be achieved. (C) Deviation of tuning frequency when using a motor antenna. In order for the above-mentioned fine tuning principle to be realized by the circuit of Japanese Patent Laid-Open No. 3-145339, the electric field strength of the desired receiving electric field station must be constant with respect to the time axis. Also S
There must be sufficient strength for the meter output to fluctuate in response to changes in tuning frequency. However, for example, in the case of an AM radio receiver for a vehicle, a motor antenna is often adopted, but when combined with this antenna,
The following problems occur. The motor antenna normally moves up and down in synchronization with the on / off operation of the radio. Therefore, when the radio is turned on from the off state, the antenna starts rising. Change in S-meter output voltage at this time of the radio is shown in FIG. In the figure, the antenna starts to rise when the radio is turned on at T _{1 and the} antenna rise operation is completed at T ₂ , and the curve A shows the S meter voltage when a station with a strong electric field strength is received, and the curve B shows a station with a weak electric field strength. Shows the S meter voltage when receiving the. Referring now to fine tuning control for receiving stations of the electric field intensity corresponding to curve A when the antenna full extension, the tuning frequency is shown in FIG. 9 f
_It becomes ₀ , which is the best reception state. But off once the radio and turn on again, because the antenna begins to rise from the state of complete housing, S meter voltage radio Figure 8
Like rises with time. Therefore, if the fine tuning control is performed at this time, as shown in FIG. 8 , the peak of the S meter voltage comes to f ₀ 'which is shifted to the higher side than the true tuning frequency f ₀ . Therefore, the best reception condition cannot be obtained. Similarly, if the station having the electric field strength corresponding to the curve B is similarly finely tuned and controlled when the radio is turned on and the antenna rises, the S meter voltage does not change until the time T ₂ shown in FIG. Therefore S
The peak of the meter voltage cannot be obtained. This peak is required after T ₂ . In this case as well, the deviation of the tuning frequency occurs as described above. A new problem here is that it takes a long time until the peak of the S meter voltage is obtained, and an unpleasant sound is generated.

Next, the latter Japanese Patent Laid-Open No. 3-158016, A
The M radio receiver has the following problems. (D) For example, in the case of an on-vehicle radio receiver, the electric field strength of the desired receiving station is constantly changing. Consider the case where the maximum digital signal is stored at a weak electric field by the above conventional receiver method. In the case of a weak electric field, the S meter output level naturally becomes low. Thus in range for the maximum value determination, when there is S meter output level and comparable level noise when a weak electric field and thus to determine the maximum value of the noise in the way, as shown in FIG. 11 A wrong signal will be generated from the fine tuning circuit, and the tuning frequency of the RF tuning circuit will not be optimum. In an extreme case, even when the S meter output is close to zero, the maximum value is set to a value somewhere within the range of maximum value determination, so that the tuning frequency of the RF tuning circuit is not optimal even if the electric field strength increases. . As a method of solving the above problems, there is a method of setting a reference voltage that can mask noise and discriminating the maximum value with respect to the S meter output voltage higher than that value. But consider the variation of the S meter output voltage, setting the reference voltage for a mask, FIG. 10
As shown in, even if the electric field strength is practically audible, it is masked. (E) Further, in the case of a weak electric field such that the maximum value of the S-meter output voltage cannot be discriminated or, in an extreme example, in the case of a frequency without a broadcasting station, the maximum value of the S-meter output voltage cannot be obtained by the receiver, which is optimum I can't find the point of synchronization.

A first object of the present invention is to provide an AM radio receiver capable of discriminating the maximum S meter output even in a weak electric field without being affected by variations in S meter output voltage and noise. .

A second object of the present invention is to provide an AM capable of searching for and receiving an optimum tuning point even in a weak electric field whose electric field strength is substantially zero.
To provide a radio receiver.

[0009]

[0010]

[0011]

In order to achieve the first object, the first invention comprises a tuning circuit and a receiving circuit connected to the tuning circuit, and at least the receiving circuit is provided. In an AM radio receiver provided with a control circuit for performing various controls including control of a tuning frequency of the tuning circuit based on electric field strength data, the control circuit is configured to perform tuning by gradually changing the tuning frequency of the tuning circuit in small increments. A first means for generating a control signal, and a second means for adding the electric field strength data every time the tuning control signal is changed and storing the maximum value of the highest electric field strength data in the tuning control signal change. Means, a third means for calculating an average value of the electric field intensity data by the sequentially changed tuning control signal, a difference between the maximum value and the average value is obtained, and it is determined whether or not the difference exceeds a predetermined value. Fourth And summarized in that a means, a.

In order to achieve the second object, the second
Of the present invention includes a tuning circuit and a receiving circuit connected to the tuning circuit, and performs various controls including control of the tuning frequency of the tuning circuit based on at least electric field strength data from the receiving circuit. In an AM radio receiver provided with a control circuit, the control circuit includes a first means for generating a tuning control signal for sequentially and gradually changing the tuning frequency of the tuning circuit, and the tuning circuit for each tuning control signal. Second means for adding the electric field strength data and storing the maximum value of the highest electric field strength data among the tuning control signal changes, and calculating an average value of the electric field strength data by the sequentially changed tuning control signals. Third means, fourth means for obtaining a difference between the maximum value and the average value, and determining whether the difference is below a predetermined value, and the tuning control signal based on the determination result of the fourth means. the S Largest fifth means and the electric field intensity data detected by means of said 5 that detects the field intensity data for respective change is sequentially changed from one of the upper or lower limit of the maximum value determining range over data output to the other And a sixth means for determining a value and an average value, and determining the presence or absence of a peak of the electric field strength signal based on the maximum value and the average value.

[0013]

[0014]

[0015]

In the AM radio receiver of the first invention, the average value and the maximum value of the electric field strength data obtained by changing the tuning control signal are obtained, and if the difference is not less than the predetermined value, the tuning frequency at that time is Optimal.

In the AM radio receiver of the second invention, when the difference is less than a predetermined value, it is determined that there is no peak (tuning point), the maximum value determination operation is continued, and the electric field strength increases and the maximum value is reached. When the discrimination becomes possible, the signal is received at the optimum tuning point.

[0017]

[0018]

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the configuration of an AM radio receiver to which the present invention is applied. 1 is an RF tuning circuit, 1a and 1b are first and second RF output terminals, and 2 is an R terminal provided at these output terminals.
10. A selection circuit for selecting one of the F output signals, 3 is a first local oscillation circuit, and 4 is a mixture of the RF output signal selected by the selection circuit 2 and the output signal of the first local oscillation circuit 3.
The first mixing circuit 5 outputs the first IF signal of 7 MHz, and 5 is I
F tuning circuit, 6 is the second local oscillation circuit, 7 is 450 KHz by mixing the first IF signal and the output signal of the second local oscillation circuit
2 is a second mixing circuit for outputting the second IF signal, 8 is an IF amplifier, and 9 is an AM detection circuit.

Reference numeral 10 is an electric field intensity detection circuit (S meter voltage output circuit), 11 is a D / A conversion circuit, 12 is a buffer circuit, 13 is an IF count buffer circuit, and 14 is a low pass filter (LPF). Further, 15 is a control microcomputer, 16 is a communication buffer circuit, 17 is a display, and 18 is a key matrix. 2 to 13
Each circuit of 16 and 16 is composed of an AM-IC circuit.

The control microcomputer 15 has an S meter output voltage DO (field strength data) from the field strength detection circuit 10, an output signal (tuning frequency data) OSC from the first local oscillation circuit 3, and an IF from the IF amplifier 8. Signal IF
Upon receiving the (desired receiving station confirmation signal), the communication buffer circuit 16 receives the enable signal CE and the clock signal CLOC.
K, damping data signal DATA, etc. are sent to perform damping setting, tuning, and periodical ultrafine tracking for avoiding saturation of the S meter output. Further, the AM-IC circuit performs an operation for obtaining the optimum value of the tuning point based on the value of the S meter output voltage at that time.

Next, the outline of the tuning tracking operation will be described. Now, in order to perform automatic tuning, the key matrix 18
If the automatic tuning key (not shown) arranged at the position is selected and operated, the control microcomputer 15 starts tuning and the tuning signal VT causes the varicap 3a of the first local oscillation circuit 3 to operate. When the presence of the station is detected by the IF signal IF, the change in the oscillation frequency is stopped by changing the capacity to change the oscillation frequency. In the automatic channel selection state, the selection circuit 2 selects the wideband RF signal output to the first RF output terminal 1a according to a command from the microcomputer 15 via the communication buffer circuit 16.

When the automatic tuning operation is stopped, a digital control signal for determining the tuning frequency of the RF tuning circuit 1 is output from the microcomputer 15 via the communication buffer circuit 16 and converted into an analog signal by the D / A conversion circuit 11. It is converted and applied to the RF tuning circuit. As a result, the tuning frequency of the RF tuning circuit 1 becomes the RF of the station currently being received.
Coarse tuned to the signal frequency.

After that, the tuning frequency of the RF tuning circuit 1 is fine-tuned by the microcomputer 15. That is, the microcomputer 15 outputs a fine tuning digital control signal, converts it into an analog signal by the D / A conversion circuit 11 and applies it to the RF tuning circuit 1 to change its tuning frequency. In response to this, the S meter output level of the electric field strength detection circuit 10 changes, so that a fine tuning digital control signal for obtaining the maximum S meter output level is determined and given to the RF tuning circuit 1. As described above, the conventional method has various problems when a weak electric field is applied. Therefore, the present invention employs the following tuning control method.

First, in the first invention, the microcomputer 15 is provided so that the optimum tuning point can be obtained even in the case of a weak electric field.
Operates as follows. That is, the microcomputer 15 changes the digital control signal to change the tuning frequency of the RF tuning circuit within the range where the maximum value of the S meter output is determined, and the electric field strength detection circuit 10 detects the S meter voltage. The value of the S meter output is added every time the digital control signal is changed. At the same time, the magnitude of the S meter output value is compared, and the greater value is stored in memory. Finally, the average value of the S meter output values is calculated from the total value of the S meter output values and the number of times the digital control signal is changed. If the difference between the maximum value and the average value stored in the memory is a certain value or more, the tuning frequency of the RF tuning circuit at that time is considered to be optimum.

2 and 3 are flowcharts showing an operation example of the microcomputer 15 described above. In the figure, step S1: determines whether the AM-IC circuit is stopped. Step S2: If stopped, the stop mode of the AM-IC circuit is set and the process ends. Step S3: If not stopped, it is determined whether the AM-IC circuit is in the stop mode. Step S4: If it is the stop mode, initialization is performed. Step S5: It is determined whether the power supply is on or the band is switched after the initialization is performed or the mode is not the stop mode. Step S6: If yes, the AM-IC circuit is initialized. Step S7: No or after initialization, S
Set the meter input mode and transfer. Step S8: Input the transferred S meter voltage. Step S9: A damping value is set according to the S meter voltage to avoid saturation of the S meter output. Step S10: Set and transfer initial data for tuning and fine adjustment (digital control signal). Step S11: Transfer the fine adjustment data. Step S12: It is determined whether or not the switching to the ultrafine adjustment is performed, and if the result is NO, a waiting time of 3 ms, and if YES, a waiting time of 50 ms has elapsed and the process proceeds to step S13. Step S13: Input the S meter voltage. Step S14: Add the input S meter voltage value. Step S15: The magnitudes of the input S meter voltage values are compared, and the larger value of them is stored in memory to detect the peak of the S meter output. Step S16: It is determined whether or not the mode is the ultrafine adjustment mode,
If yes, go to step S19, if no, go to step S17. Step S17: It is determined whether or not the fine adjustment operation of Steps S11 to S17 has been repeated 81 times. If no, the process returns to step S11, and if yes, step S18.
go to. The 81 stages are arbitrarily set depending on the number of circuit elements and the like. Step S18: A fine adjustment search start point is determined for the five peaks obtained by the fine adjustment operation. Step S19: It is determined whether or not the ultrafine adjustment operations of steps S11 to S16 and S19 are repeated 10 stages. If NO, the process returns to step S11, and if YES, the process goes to step S20. Step S20: Set and transfer the peak data of the S meter output obtained by the ultrafine adjustment operation. Step S21: Cancel the mute performed before entering step S5. Step S22: Calculate the average value of the S meter output. Step S23: If the difference between the maximum value and the average value of the S meter output is equal to or more than a predetermined value (for example, 1.2 V), the above tracking is ended, and if the difference is less than the above, tracking according to the second invention described later is performed.

As described above, in the embodiments shown in FIGS. 2 and 3, the fine adjustment is performed in two steps so that the tuning accuracy is high. In the case of a weak electric field, the maximum value of the S meter output voltage is naturally low, and as shown in FIG. 10 , it can be considered that the average value and the noise floor of the S meter output voltage are almost the same. Therefore, even if the noise floor of the S meter output voltage varies, the average value changes similarly. As described above, when setting the mask voltage as in the conventional case, in consideration of this variation, a sufficiently high value with respect to the noise floor must be adopted, but if the average value is used, the variation does not have to be considered. . Further, since the difference between the average value and the maximum value can be reduced to a value that is not affected by noise, it is possible to determine the optimum value of the tuning point up to a weak electric field.

Next, in the second aspect of the invention, even in the case of a weak electric field where the maximum value of the S meter output cannot be detected, the maximum value detection operation is continued within a certain range, and the electric field strength rises to reach the maximum value. Is detected, the detection operation is stopped so that optimum reception is possible as a reception state at the maximum value, and the microcomputer 15 performs the following operation.

That is, the microcomputer 15 detects the S-meter output by changing the digital control signal within the range for determining the maximum value of the S-meter output, calculates the average value of the total values, and calculates the average value. Find the difference between the value and the maximum value,
If the difference is less than a certain value, it is determined that there is no peak. When there is no peak, the reception state is set in the middle of the maximum value determination range and the mute is released. In that state, the digital control signal is slowly decreased to reach the lower limit of the maximum value determination range. Then, the digital control signal is slowly increased from the lower limit to the upper limit, and the S meter output is detected every time the digital control signal is changed. The average value is obtained from the total value of the detected S meter outputs, and the presence or absence of a peak is determined from the average value and the maximum value. As a result, when there is no peak, the digital control signal is slowly changed to the lower limit again, and the peak is detected again from the lower limit.
When there is a peak, the digital control signal is slowly changed toward the peak point.

FIG. 4 is a flowchart showing an example of the above-mentioned operation of the microcomputer 15, which is step S2 in FIG.
It follows on from 3. Step S24: It is determined whether or not the difference between the average value and the peak value of the S meter output is within a fixed value (for example, 0.1 V). If the result is no, the process ends, but if yes, the process proceeds to step S25. Step S25: Since it is determined that there is no peak, the intermediate value of the maximum value determination range (81 steps) is set as the assumed value (default value) of the digital control signal and transferred. Step S26: The digital control signal is smoothly changed to the default value to bring it into the tuning reception state. Step S27: In that state, the regular tracking shown in FIG. 4 is performed. Step S28: The presence or absence of a peak is discriminated from the average value and the maximum value of the S meter output thus obtained. If there is no peak, the process returns to step S24. Step S29: When there is a peak, the digital control signal is changed step by step up to the peak value. Step S30: Input the S meter output voltage and return to step S24.

FIG. 5 is a flow chart showing the operation of the microcomputer 15 which performs regular tracking. Step S27a: The fine adjustment data below one step is transferred, and the digital control signal is slowly decreased to the lower limit of the maximum value determination range. Step S27b: It is determined whether or not the reduction operation up to the lower limit is performed in 40 steps. If no, step S27
Returning to step a, if yes, go to step S27c. Step S27c: The fine adjustment data in one step is transferred, and the digital control signal is slowly increased from the lower limit to the upper limit. Step S27d: Input the S meter output voltage. Step S27e: The S meter output value is added. Step S27f: The peak of the S meter output is detected by comparing the magnitudes of the S meter output values and storing the larger value. Step S27g: It is determined whether or not the operation from Step S27c to S27g has been performed 81 times. If NO, the process returns to step S27c, and if YES, the process proceeds to step S27h. Step S27h: Calculate the average value of the S meter output values.

As described above, in the embodiment shown in FIG. 11 , a weak electric field such that the maximum value of the S meter output cannot be discriminated, or even if there is no electric field, optimum reception can be performed if the electric field strength increases. Note that these operations can be performed slowly while the mute is released so that the user does not feel discomfort.

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

As described above, according to the present invention, the AM of the system for detecting the maximum value of the output signal (S meter output) of the electric field strength detection circuit which changes according to the change of the tuning frequency.
In radio receiver, without being affected by variations or noise S meter output, Ru can determine the optimum tuning point even in a weak electric field.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an AM radio receiver to which the present invention is applied.

FIG. 2 is a flow chart for explaining the operation of the embodiment of the first invention.

FIG. 3 is a flowchart for explaining the operation of the embodiment of the first invention.

FIG. 4 is a flow chart for explaining the operation of the embodiment of the second invention.

FIG. 5 is a flowchart showing a subroutine of regular tracking.

FIG. 6 is a song showing the relationship between the desired electric field strength and the S meter voltage.
It is a diagram.

FIG. 7 is a curve showing the relationship between the tuning frequency and the S meter voltage.
It is a figure.

FIG. 8 shows an AM radio receiver having a motor antenna .
FIG. 6 is a curve diagram showing a temporal change of the S meter voltage in FIG.

FIG. 9 Tuning frequency and S meter voltage in the above receiver
It is a curve figure which shows the relationship with.

FIG. 10 shows a case where a microphone voltage is set in the receiver .
A curve diagram showing the relationship between the tuning frequency and the S meter voltage
is there.

FIG. 11: Tuning frequency and S meter voltage according to electric field strength
It is a curve figure which shows the relationship with.

[Explanation of symbols]

1 RF tuning circuit 3 First local oscillator circuit 4 First mixing circuit 5 IF tuning circuit 6 Second local oscillator circuit 7 Second mixing circuit 9 AM detection circuit 10 Electric field strength detection circuit 11 D / A conversion circuit 15 Control microcomputer

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-327417 (JP, A) JP-A-5-63512 (JP, A) JP-A-62-35707 (JP, A) 39034 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H03J ⁷ /02-7/28 H03J 3/28 H04B 1/18

Claims (2)

(57) [Claims] 1. A tuning circuit and a receiving circuit connected to the tuning circuit, and various controls including control of a tuning frequency of the tuning circuit based on at least electric field strength data from the receiving circuit. In an AM radio receiver having a control circuit for performing the above, the control circuit includes a first means for generating a tuning control signal for sequentially and gradually changing the tuning frequency of the tuning circuit, and each time the tuning control signal is changed. Second means for adding the electric field strength data and storing the maximum value of the highest electric field strength data among the changes in the tuning control signal; and calculating an average value of the electric field strength data according to the sequentially changed tuning control signal. An AM radio receiver, comprising: a third means for performing the above, and a fourth means for determining a difference between the maximum value and the average value and determining whether the difference exceeds a predetermined value. 2. A tuning circuit and a receiving circuit connected to the tuning circuit, and various controls including control of a tuning frequency of the tuning circuit based on at least electric field strength data from the receiving circuit. In an AM radio receiver having a control circuit for performing the above, the control circuit includes a first means for generating a tuning control signal for sequentially and gradually changing the tuning frequency of the tuning circuit, and each time the tuning control signal is changed. Second means for adding the electric field strength data and storing the maximum value of the highest electric field strength data among the changes in the tuning control signal; and calculating an average value of the electric field strength data according to the sequentially changed tuning control signal. And a fourth means for determining the difference between the maximum value and the average value and determining whether the difference is below a predetermined value, and the tuning control based on the determination result of the fourth means. Belief The
Fifth means for sequentially changing from one of the upper limit or the lower limit of the maximum value determination range of the S meter output to the other and detecting the electric field strength data for each change, and the maximum of the electric field strength data detected by the fifth means And a sixth means for determining a value and an average value and determining the presence or absence of a peak of the electric field intensity signal based on the maximum value and the average value.