JPH1168519A - Automatic tuning device for receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform automatic tuning at a high speed. SOLUTION: A controller 20A makes a synchronization frequency switched successively by setting a frequency-dividing ratio corresponding each channel from CH1 to CH20 in a PLL circuit 4. At this time, it is discriminated if an output of a reception level detection circuit 30 rises higher than a fixed output only for 20 ms, after being switched to a synchronization frequency and then the PLL circuit is locked. When it does not rise, it is judged that there is no station and immediately the next synchronization frequency is switched to. Conversely, when the output of the reception level detection circuit 30 rises higher than the fixed level, it is discriminated and further if an output of a noise level detection circuit 13 decreases below the fixed level and when it lowers, it is discriminated that a station is present and the synchronization frequency is fixed. When it does not lower, it is discriminated that no station is present, and the next synchronization frequency is switched to.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic channel selecting device for a receiver, and more particularly to an automatic channel selecting device for a receiver capable of executing a channel selecting operation at high speed.

[0002]

2. Description of the Related Art A receiver is provided with an automatic tuning function so that a user does not have to search for a station by manual tuning operation. This automatic channel selection function is realized by, when a user instructs automatic channel selection, the controller searching for a station while sequentially switching the tuning frequency of the receiver, and fixing the station at the tuning frequency of the station. FIG. 5 shows the configuration of a conventional FM receiver with an automatic tuning function. The received signal of antenna 1 is RF
After being amplified by the amplifier 2 at high frequency, the signal is mixed by the mixer 3 with the local oscillation signal input from the PLL circuit 4 and converted into an intermediate frequency signal. The intermediate frequency signal is subjected to IF amplification and amplitude limitation by an IF amplifier 5 and then input to an FM detector 6 where it is subjected to FM detection. The audio signal demodulated by the FM detection is input to the AF amplifier 8 via the cutoff circuit 7, power-amplified, and output to the speaker 9.

The PLL circuit 4 oscillates at a frequency corresponding to the magnitude of the control voltage, and outputs a local oscillation signal.
And a PLL-IC 11 that divides the output of the VCO 10 by a variable dividing ratio, compares the phase with a reference frequency signal, and outputs a phase difference signal, and a low-frequency component of the phase difference signal output from the PLL-IC 11 Take out, and as control voltage V
It comprises an LPF 12 that outputs to the CO 10. F
The M detector 6 is connected to a noise level detection circuit 13 for detecting a high frequency noise level in the demodulated signal. As shown in FIG. 6, the noise level detection circuit 13 includes an HPF 14 for extracting a high frequency noise component (for example, a component of 30 kHz or more) of the demodulated signal, and a noise amplifier 15 for amplifying the high frequency noise component extracted by the HPF 14. And a rectifying / smoothing circuit 16 for rectifying and smoothing the output of the noise amplifier 15. The rectifying / smoothing circuit 16 outputs a noise level detection signal of a DC voltage. The noise level detection signal takes a voltage value having a magnitude proportional to the magnitude of the noise level. If the noise level detection signal is below a certain level during reception by a certain station, the controller 20 of the microcomputer makes the input and output of the shutoff circuit 7 conductive, and the speaker 9
When the noise level detection signal exceeds a certain level, the shutoff circuit 7 is turned off to prevent noise from being output (squelch function).

The controller 20 stores frequency data for 20 channels from CH1 to CH20 in a built-in memory (not shown). When the user wants to search for a station from each channel, the channel search key 21 is pressed. , A channel search command is given. Then, the controller 20 sets the shutoff circuit 7 to the shutoff state according to the flowchart of FIG.
1 frequency division ratio D (CH1) corresponding to frequency F (CH1)
Is set in the PLL-IC 11 (steps S2 and S2).
3) Wait for a locked state (step S4). P
The LL circuit 4 pulls in the oscillation frequency of the VCO 10 so as to be D (CH1) times the reference frequency signal, and outputs a lock signal from the PLL-IC 11 upon completion.

[0005] Until the receiver tunes to CH1, the high-frequency noise component in the demodulated signal is large, and the noise level detection circuit 13 outputs a large noise level detection signal. When tuning to CH1 is completed, the noise level detection signal remains large if there is no station on CH1 (see broken line B in FIG. 8), but if there is a station, the high-frequency noise component in the demodulated signal is reduced. The noise level detection signal gradually decreases according to the time constant of the rectifier / smoothing circuit 16 (see the solid line A in FIG. 8).

After outputting the frequency division ratio of CH1, the controller 20 waits until a lock signal is input, and when the lock signal is input, starts a timer for measuring 70 ms (YES in step S4, S5), the timer until the time is up, the noise level detection signal output from the noise level detecting circuit 13 determines whether or falls below a predetermined reference value N _C (step S6, S7). The noise level detection signal is N _C until the time is up.
, The tuning frequency is fixed, the cutoff state of the cutoff circuit 7 is released, the input and output are made conductive so that CH1 can be heard, and the automatic channel selection control processing ends (step S6). YES, S8).

On the other hand, when the noise level detection signal does not fall below N _C before the time is up,
It is determined that there is no station of CH1 (YES in step S7), and then the frequency division ratio D corresponding to the frequency F (CH2) of CH2
(CH2) is set in the PLL-IC 11 (step S
9, S10, S3), and waits for a locked state (step S4). If a lock signal is input, the presence or absence of a CH2 station is determined using the noise level detection signal in the same manner as in the case of CH1, and if there is a station, the tuning frequency is fixed (steps S5 to S7, S8). If not, the same processing is performed for CH3 and thereafter (steps S9, S10, S3).
If there is no station up to the last CH20, the cutoff state of the cutoff circuit 7 is released, and the automatic channel selection control processing ends (YES in step S9, S8).

[0008]

However, in the above-described conventional automatic channel selection method, when there is no station for a certain channel CHi, the oscillation frequency of the VCO 10 of the PLL circuit 4 is locked to the frequency corresponding to the CHi. After that, it takes as long as 70 ms to complete the determination of the absence of a station using the noise level detection signal. This is because the rectifying / smoothing circuit 16 of the noise level detection circuit 3 has a large time constant to suppress the noise component remaining in the noise level detection signal, so that when the station is received, the noise level detection signal is correctly generated. Controller 2
This is because the erroneous determination of 0 prevents the capacitor of the rectifying / smoothing circuit 16 from discharging, which slows down the response speed of the noise level detection signal when the station is received. As described above, in the related art, a processing time of about 70 ms is required per channel in addition to the lock-up time of the PLL circuit 4, so that when there are ten to several tens of channels, it takes a lot of time for automatic channel selection. There was a problem. The present invention has been made in view of the above-described problems of the related art, and has as its object to provide an automatic tuning apparatus for a receiver that can perform automatic tuning at high speed.

[0009]

SUMMARY OF THE INVENTION An automatic tuning apparatus for a receiver according to the present invention has a variable tuning frequency, a receiving means for receiving, demodulating and outputting radio waves, and a high frequency noise level during demodulation output. Noise level detecting means for detecting, receiving level detecting means for detecting the receiving level at the receiving means, and tuning control means for searching for a station while sequentially switching the tuning frequency of the receiving means, and fixing the tuning frequency at the station. The tuning control means, when determining the presence or absence of a station at a certain tuning frequency, first determines whether or not the reception level detected by the reception level detection means has risen above a certain level, and if not, the station If the reception level rises above a certain level, it is further determined whether or not the noise level detected by the noise level detecting means has fallen below a certain level. And, when not lowered is characterized, it has to be determined that no station. The reception level detecting means has a fast rising response when the station is received, and when tuning to a certain frequency during automatic channel selection, the output of the receiving level detecting means rises above a certain level within a certain predetermined short period of time. If there is no station, it is immediately determined that there is no station, and the frequency is switched to the next tuning frequency, so that automatic tuning can be performed at a very high speed.

[0010]

Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of an FM receiver with an automatic tuning function according to the present invention. The same components as those in FIG. 5 are denoted by the same reference numerals. The signal received by the antenna 1 is amplified by the RF amplifier 2 at high frequency,
The signal is mixed with the local oscillation signal input from the LL circuit 4 and converted into an intermediate frequency signal. The intermediate frequency signal is subjected to IF amplification and amplitude limitation by an IF amplifier 5 and then input to an FM detector 6 where it is subjected to FM detection. The audio signal demodulated by the FM detection is input to the AF amplifier 8 via the cutoff circuit 7, power-amplified, and output to the speaker 9.

The PLL circuit 4 oscillates at a frequency corresponding to the magnitude of the control voltage and outputs a local oscillation signal.
And a PLL-IC 11 that divides the output of the VCO 10 by a variable dividing ratio, compares the phase with a reference frequency signal, and outputs a phase difference signal, and a low-frequency component of the phase difference signal output from the PLL-IC 11 Take out, and as control voltage V
It comprises an LPF 12 that outputs to the CO 10. F
A noise level detection circuit 13 for detecting a high-frequency noise level in the demodulated signal is connected to the M detector 6 (see FIG. 6 for the configuration of the noise level detection circuit 13). If the noise level detection signal detected by the noise level detection circuit 13 is less than or equal to a certain value during reception by a certain station, the controller 20A of the microcomputer makes the cutoff circuit 7 conductive between the input and output, and When the noise level detection signal exceeds a certain level, the cutoff circuit 7 is cut off to prevent noise from being output (squelch function).

The IF amplifier 5 is connected to a reception level detection circuit 30 for detecting the reception level by detecting the level of the intermediate frequency signal before the amplitude limit. As shown in FIG. 1, the reception level detection circuit 30 includes an amplifier 31 for amplifying the intermediate frequency signal and a rectification / smoothing circuit 32 for rectifying and smoothing the output of the amplifier 31. 32 outputs a DC voltage reception level detection signal. The reception level detection signal takes a voltage value having a magnitude proportional to the magnitude of the reception level. The time constant of the rectification / smoothing circuit 32 of the reception level detection circuit 30 is set shorter than the time constant of the rectification / smoothing circuit 16 of the noise level detection circuit 13. This rectifying / smoothing circuit 32 has a fast rising response when a station is received (see the solid line A in FIG. 2).

The controller 20A stores frequency data for 20 channels from CH1 to CH20 in a built-in memory (not shown). When a user presses a channel search key 21 and a channel search command is given, an automatic operation is performed. Execute the tuning control process. At this time, the presence or absence of a station having a certain tuning frequency is determined by the reception level detection circuit 30.
, And the noise level detection signal output from the noise level detection circuit 13.

Next, the operation of the above embodiment will be described with reference to FIGS. FIG. 2 shows the reception level detection circuit 3.
FIG. 3 is a flow chart showing an automatic tuning control process by the controller 20A. When the user presses the channel search key 21 to give a channel search command, the controller 20A sets the cutoff circuit 7 to the cutoff state (step S51 in FIG. 2), first sets i = 1 (step S52), and sets CH1 to CH1. Frequency F
The division ratio D (CH1) corresponding to (CH1) is
It is set to C11 (step S53), and waits for a locked state (step S54). PLL circuit 4 is a VCO
10 is pulled up so that the oscillation frequency of the reference frequency signal becomes D (CH1) times the reference frequency signal.
Outputs a lock signal.

Until the receiver tunes to CH1, the level of the intermediate frequency signal is low and the reception level detection circuit 30
Outputs a small reception level detection signal. When tuning to CH1 is completed, the reception level detection signal remains small if there is no station of CH1 (see broken line B in FIG. 2).
If there is a station, the level of the intermediate frequency signal increases,
The reception level detection signal rises with a response delay of about s (see the solid line A in FIG. 2). Until the receiver finishes tuning to CH1, the high-frequency noise component in the demodulated signal is large,
The noise level detection circuit 13 outputs a large noise level detection signal. When you have finished tuning to CH1,
If there is no 1 station, the noise level detection signal remains large (see broken line B in FIG. 8), but if there is a station, the high-frequency noise component in the demodulated signal is reduced, and the noise level detection signal is about 70 ms. It falls due to the response delay (see the solid line A in FIG. 8).

After outputting the frequency division ratio of CH1, the controller 20A waits until a lock signal is input. If the lock signal is input, the receiver has finished tuning to CH1, and then starts a first timer that measures t ₁ = 20 ms (steps S54 and S55). Until the first timer times out, the reception level detection signal output from the reception level detection circuit 30 becomes R
_{It is} determined whether or not the value has exceeded _C (steps S56, S
57). When tuning to CH1, if there is a station, the reception level detection signal immediately rises and exceeds R _C with only a response delay of about 20 ms, but remains small if there is no station.

Here, when the timer does not exceed R _C before the first timer expires, the controller 20
A determines that there is no station (YES in step S57). Since the last channel has not been completed yet, i is set to 2 (NO in step S58, S59), and immediately the minute corresponding to the frequency F (CH2) of CH2 is set. The circumference ratio D (CH2) is P
It is set in the LL-IC 11 and waits for a locked state (steps S53 and S54). After the lock, the first timer is started again (step S55), and the reception level detection circuit 30 is operated until the first timer times out.
It is determined whether or not the reception level detection signal output from the above has risen above R _C (steps S56 and S57).

In this case as well, when the timer does not exceed R _C before the first timer expires, the controller 20
A determines that there is no station (YES in step S57), and determines the frequency division ratio D (CH) corresponding to the next frequency F3 (CH3) of CH3.
3) is set in the PLL-IC 11 (step S58,
After locking, the first timer is started (steps S54 and S55), and the reception level detection signal output from the reception level detection circuit 30 becomes R _C or more before the first timer times out. It is determined whether it has risen (steps S56 and S57).

Thereafter, the same processing is repeated to search for a channel whose reception level detection signal has risen to R _C or more while switching the tuning channel. At this time, about 20 times per channel other than the lock-up time of the PLL circuit 4
Since only a processing time of ms is required and the time is about 50 ms shorter than that of the related art, each channel can be searched at high speed (see FIG. 4).

Thereafter, for example, when tuning to the channel CH9 and the reception level detection signal rises above R _C , the controller 20A determines YES in step S56, but at this time, it is not determined that there is still a receiving station. This is because, despite the fact that there is no station of CH9, there is a possibility that the reception level detection signal has risen to R _C or more because it has caught external noise or has been disturbed by other stations. If there is no receiving station just because external noise is caught or interference from other stations occurs, a high-frequency noise component is present in the demodulated signal.
The noise level detection signal falls at about s (see the solid line A in FIG. 8). Then, after determining YES in step S56, the controller 20A starts a second timer for measuring t ₂ = 50 ms (step S60), and until the second timer times out, the noise level detection circuit 13 noise level detection signal output from it is determined whether or not lower than a predetermined reference value N _C (step S6
1, S62).

If the noise level detection signal falls below N _C before the second timer times out, the controller 20A determines that the station of CH9 is present (Y in step S61).
ES), the tuning frequency is fixed, the cutoff state of the cutoff circuit 7 is released so that CH9 can be heard, and the automatic channel selection control processing ends (step S63). If the noise level detection signal does not fall below N _C before the second timer expires, it is determined that CH 9 has no station (YES in step S 62). , I are incremented (steps S58 and S59), and the process returns to step S53 to search for a receiving station from the channel CH10 and subsequent channels in the same manner as described above. If there is no station up to the last CH20, the cutoff state of the cutoff circuit 7 is released, and the automatic channel selection control processing ends (YES in step S59, S63).

According to this embodiment, at the tuning frequency of each channel switched for automatic channel selection,
The determination of the absence of a receiving station is performed by monitoring a received level detection signal that responds in about 20 ms if a receiving station is present, so that a noise level detection signal that requires about 70 ms in response as in the related art is monitored. , About 50 ms, the determination is completed in a short time. Therefore, for example, when there are 20 channels to be automatically selected and there are no stations in all 20 channels, the entire search time can be reduced by 50 ms × 20 = 1 second (see FIG. 4).

In the above-described embodiment, a case has been described as an example where a large number of channel frequencies stored in the built-in memory of the controller are searched. However, a predetermined frequency band (for example, 25kHz, 5
The same applies to the case of searching for a station while increasing or decreasing the tuning frequency at 0 kHz, 100 kHz, etc.).

[0024]

According to the present invention, at each tuning frequency which is switched for automatic channel selection, the absence of a receiving station is determined by using a reception level detection signal which responds promptly if there is a receiving station. Therefore, automatic tuning can be performed at extremely high speed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an FM receiver with an automatic tuning function according to an embodiment of the present invention.

FIG. 2 is a diagram showing detection characteristics of a reception level detection circuit.

FIG. 3 is a flowchart showing an automatic tuning control process by a controller in FIG. 1;

FIG. 4 is an explanatory diagram showing the automatic tuning speed of the receiver of FIG. 1 and a conventional receiver in comparison.

FIG. 5 is a block diagram of a conventional FM receiver with an automatic tuning function.

6 is a block diagram showing a configuration of a noise level detection circuit in FIG.

FIG. 7 is a flowchart showing an automatic tuning control process by the controller in FIG. 5;

FIG. 8 is a diagram illustrating detection characteristics of a noise level detection circuit.

[Explanation of symbols]

Reference Signs List 1 antenna 2 RF amplifier 3 mixer 4 PLL circuit 5 IF amplifier 6 FM detector 7 cutoff circuit 8 AF amplifier 9 speaker 13 noise level detection circuit 20A controller 21 channel search key 30 reception level detection circuit

Claims (1)

[Claims] 1. A receiving means which receives a radio wave, demodulates and outputs a variable tuning frequency, a noise level detecting means for detecting a high-frequency noise level in the demodulated output, and detects a receiving level at the receiving means. The station is searched while sequentially switching the tuning frequency of the receiving level detecting means and the receiving means,
Tuning control means for fixing at a tuning frequency of the station, the tuning control means, when determining the presence or absence of a station at a certain tuning frequency, first the reception level detected by the reception level detection means is more than a certain If the reception level has risen above a certain level, it is further determined whether the noise level detected by the noise level detection means has fallen below a certain level. Discriminating, when it falls below a certain level, it is determined that there is a station, and when it does not fall, it is determined that there is no station.