JPH0311950Y2 - - Google Patents

Description

[Detailed description of the invention] "Purpose of the invention" (Industrial application field) The present invention relates to an automatic tuning circuit. The present invention relates to a circuit for automatically tuning into a broadcasting station.

(Prior art) In recent years, when a radio receiver is installed in a car and receives broadcasts while moving, it automatically detects when the reception condition of the receiving broadcast station deteriorates and scans the frequency. Various automatic tuning circuits have been proposed that are capable of tuning to a broadcasting station with good reception.

This type of automatic tuning circuit, for example, as shown in FIG. 4 as a conventional automatic tuning circuit, has an FM circuit section 3
The signal input from the 0 or AM circuit section 31 to the detection stage 32 is set to a high level (hereinafter abbreviated as H) or a low level (hereinafter abbreviated as L) depending on the presence or absence of a broadcasting station. is output as a detected output signal K. In other words, the reception condition deteriorates,
When the detection output signal K changes from H to L in the detection stage 32, the transistor Q1 connected to the CR circuit in the frequency scanning starting circuit C turns off, and the transistor Q2 turns on. Subsequently, the transistor Q3 is turned on, and by inputting this on signal to the key matrix circuit section 34 of the reception quality determination section 33, the frequency control section 35 is set to a frequency scanning state. As a result, tuning is started, but when enough broadcast stations are received to make the detection output signal K high, the on/off state of each of the transistors Q1 to Q3 is reversed, and the frequency scanning of the frequency control section 35 is stopped. It operates to tune to the broadcast station in question.

(Problem to be solved by the invention) However, in the conventional automatic tuning circuit described above, the tuning start sensitivity and tuning stop sensitivity, which are the operating points of the control signal output for starting or stopping frequency scanning, are Since the detection output signal from the detection stage was set as a reference only, the reception quality could not be detected accurately. Nakatsuta. For this reason, for example, if the receiving condition of the receiving broadcasting station deteriorates, the level of the detection output signal K drops to the tuning starting sensitivity, and frequency scanning is started, the retuned station will be at the same level as the above broadcasting station. Even if a broadcasting station is only received with good quality, if there is a station that is even slightly stronger than the above-mentioned tuning start sensitivity, frequency scanning will be stopped there and the user will be tuned to that station. Therefore, conventional automatic tuning circuits have the disadvantage that they may not always be tuned to a broadcasting station that can be well received.

The present invention was developed in view of the above points, and its purpose is to detect the electric field strength signal and the detection output signal, and to enable the tuning start sensitivity and tuning stop sensitivity to be set individually. By this,
To provide an automatic tuning circuit capable of performing ideal automatic tuning.

"Structure of the invention" (Means for solving the problems) The automatic tuning circuit according to the invention is an automatic tuning circuit for a receiver that receives a signal modulated by either FM or AM. reception quality determining means for inputting an electric field strength signal and a detection output signal and outputting a control signal for starting and stopping frequency scanning of a reception frequency control section according to the strength of each signal; and an activation level for starting the frequency scanning. The reception quality determining means includes an A/D converter, an input port, and a central processing unit. It consists of a random access memory, a read-only memory, and an output port.

Also included is a circuit in which the reference setting means is a diode matrix circuit.

(Function) The reception quality determining means is configured to receive an electric field strength signal and a detection output signal, and outputs a control signal for starting or stopping the frequency scanning of the reception frequency control section according to the strength of each signal. Works to output.

Since the standard setting means can individually set the criteria for outputting the control signal in the receiving quality determining means, it can arbitrarily set the criteria for starting the frequency scanning of the receiving frequency control section and the criteria for stopping it. Can be set individually.

(Embodiment) An embodiment of the automatic tuning circuit according to the present invention will be described based on FIGS. 1 to 3. FIG. 1 is an overall block diagram, FIG. 2 is a flowchart for explaining the operation, and FIG. 3 is a circuit diagram of the diode matrix.

In the figure, 1 shows a part of the FM circuit, and 2 shows the AM circuit.
A part of the circuit section is shown, and detection stages 3 and 4 are connected to the rear stage of each IF stage 1a and 2a, respectively. From the detection stages 3 and 4, a field strength signal S and a detection output signal (in the case of FM, a so-called positive tuning point detection signal is obtained by an S curve detection signal and a field strength signal, and a high level H at the positive tuning point, a positive A signal that is low level L outside the tuning point.In addition, in the case of AM, the field strength signal is reversed from H (or L) to L (or H) at an input level of 30 to 40 dB (about 35 dB in actual products). These signals S and SD are selected by band changeover switches S1 and S2 and input to the reception quality determining means 5. The reception quality determining means 5 operates to output a control signal P for starting or stopping the frequency scanning of the reception frequency control section 6 in accordance with the above-mentioned signals S and SD. Reference numeral 7 denotes a standard setting means, which is used to individually set a judgment standard for determining which control signal P should be output in the reception quality judgment means 5.

To explain a specific configuration example below, the reception quality determining means 5 includes an A/D converter 5a for converting the signal S into a digital signal, and an output signal from the A/D converter 5a to a central processing unit 5b.
It consists of an input port IP, a random access memory 5c, a read-only memory 5d, and an output port EP for inputting data to the central processing unit 5b. The converted signal S is divided into H and L at a certain threshold level.
The criteria converted into values and determined for the signal S, i.e.
It acts to output a control signal P that starts or stops frequency scanning based on a criterion for determining the presence or absence of a broadcast station. The reference setting means 7 is capable of independently arbitrarily varying the reference point for starting or stopping the frequency scanning, and in the embodiment, the reference point is accurately variably adjusted using a diode matrix shown in FIG. It is configured so that it can be done. Note that the reference setting means 7 is not necessarily limited to this example, and it goes without saying that a semi-fixed resistor, dip switch, or the like may be used.
In addition, in the embodiment, the reception frequency control section 6 includes a programmable divider 6a and a control voltage generation circuit 6.
b and a low-pass filter 6d, and includes a control section that outputs a control voltage Vt for controlling the oscillation frequency of the voltage-controlled oscillators 1b and 2b in the FM circuit section 1 or the AM circuit section 2, and Frequency control is performed by inputting frequency data FF, FA fed back from each voltage controlled oscillator 1b, 2b into the programmable divider 6a. Note that the prescaler 6c is for matching the frequency range on the frequency data FF side to the programmable divider 6a.

The reception frequency control section 6 is mainly used for frequency scanning, and starting or stopping of the scanning is controlled by the control signal P.

An example of the operation of the above configuration will be explained based on the flowchart shown in FIG. Here, the diode matrix frequency scan start sensitivity voltage is
Va, frequency scan stop sensitivity voltage is Vb.

First, in step 50, each of the above voltages Va and Vb is
Initial settings are made, and it is determined in step 51 whether or not to start the automatic channel selection operation, and if the affirmative branch Y is selected, the detection output signal is determined in step 52.
It is determined whether SD is at H (high level), that is, whether there is a received signal of sufficient strength. If the negative branch N is selected here, the process moves to step 53 where it is determined whether the detection output signal SD is at L (low level) for 4 seconds or more, and here the negative branch N waits to return to step 52. The routine moves to routine W.
On the other hand, the positive branch Y moves to step 54 in which the frequency a being received is stored, and frequency scanning is started.
The program then moves to the channel selection routine that returns to step 52 above.

On the other hand, the affirmative branch Y of step 52 moves to step 56 where it is determined whether or not frequency scanning is in progress.
The negative branch N moves to step 57 in which it is determined whether the electric field strength signal S is less than the frequency scan start sensitivity voltage Va for 4 seconds or more. Here, the negative branch N moves to step 52, and the affirmative branch Y moves to step 54. The positive branch Y of step 56 moves to step 58 where it is determined whether or not the field strength signal S is equal to or higher than the frequency scan stop sensitivity voltage Vb.
Then, the process moves to step 59 where frequency scanning is to be stopped, and then to step 52. The negative branch N of step 58 moves to step 60 in which it is determined whether the frequency scanning has completed one cycle. This negative branch N
The affirmative branch Y moves to step 52, while the affirmative branch Y moves to step 61, where it stops at the frequency a.
If the automatic channel selection operation is turned off (step 62), the process shifts to a standby routine that returns to step 51 above. In summary, since the evaluation criteria for the level of the signal S can be arbitrarily set in steps 57 and 58, it is possible to automatically select stations according to the reception situation, and also to tune stations that are not suitable for reception as in the past. There is no danger that you may end up selecting a channel. Also, as shown in the flowchart, each signal S
By giving a grace period of about 4 seconds when evaluating the level, it is possible to eliminate unstable factors such as fluctuations in electric field strength and noise due to the movement of the vehicle.

"Effects of the Invention" According to the automatic tuning circuit according to the present invention, it is possible to individually set whether to start or stop frequency scanning under which reception conditions. Therefore, it is not only easy to select only the stations that can be received extremely well after starting frequency scanning in a situation where the reception condition has deteriorated considerably, but also to tune in even if the level of the input signal fluctuates. Start and stop operations are not performed frequently (malfunctions can be prevented),
Stable operation is performed.

In addition, the diode lithomask circuit can be set in advance for each destination of the product, and there is no need to make adjustments during the production process, unlike when using a rotary volume, greatly improving productivity. In addition, the circuit can be simplified and implemented at low cost compared to the conventional configuration in which transistors and the like are combined.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the automatic tuning circuit according to the present invention, FIG. 1 is an overall block diagram, FIG. 2 is a flowchart for explaining the operation, and FIG. 3 is a diode matrix diagram. It is a circuit diagram. FIG. 4 is a block diagram showing the basic principle of a conventional automatic tuning circuit. 1: FM circuit section, 2: AM circuit section, 3, 4: detection stage, 5: reception quality determination means, 6: reception frequency control section, 7: reference setting means.

Claims (1)

[Claims for Utility Model Registration] 1. An automatic tuning circuit for a receiver that receives a signal modulated by either FM or AM, which inputs a field strength signal and a detection output signal, and calculates the strength of each signal. reception quality determining means for outputting a control signal for starting and stopping frequency scanning of the reception frequency control unit according to the frequency scanning; and reference setting means for separately setting stop levels, and the reception quality judgment means is comprised of an A/D converter, an input port, a central processing unit, a random access memory, a read-only memory, and an output port. Features an automatic tuning circuit. 2. The automatic tuning circuit according to claim 1, wherein the reference setting means is a diode matrix circuit.