JP2541204B2 - Auto tuning device - Google Patents

Description

The present invention relates to an automatic tuning apparatus for a tuner of a synthesizer system capable of receiving a plurality of bands such as a TV band, an FM band and an AM band.

[Outline of Invention]

In the case of multiple bands, the present invention aims to stabilize the search speed by changing the search speed of the tuning point (tuning point) according to the number of broadcasting stations in view of the fact that the number of broadcasting stations differs for each band. is there.

[Conventional technology]

To automatically scan the tuning points on the synthesizer tuner, press the search button, for example. Then, the N value of the frequency division ratio 1 / N of the variable frequency division circuit of the local oscillation circuit of the synthesizer tuner is changed, the local oscillation frequency is changed, and the reception frequency is changed. Then, at a certain tuning point of broadcasting, the change of the N value is temporarily stopped, the muting of the output is released, and sound is output for about 5 seconds, for example. If this tuning point is the desired station, the search is stopped, and if it is not the desired station, the above operation is repeated and the search is performed up to the desired station.

[Problems to be solved by the invention]

By the way, when the tuner is capable of receiving multi-bands such as AM band, FM band, and TV band, if the search speed during auto tuning is common to each band, the following problems occur.

That is, when there are many broadcasting stations such as the AM band and FM band (especially the FM band of tuners for the United States), make sure that the search time from the station with the lowest receiving frequency to the station with the highest receiving frequency is not too long. Considering this, the step of changing the N value is determined. That is, it is better to set the time interval for changing the N value relatively short.

However, if the VHF band of the television is searched at this time interval, the search speed is too fast because the number of stations is very small, and stable search cannot be performed.

However, if the search speed is adjusted to this TV band, the FM and AM bands will take too long to search.

In view of the above points, the present invention changes the search speed according to the band and limits the upper limit of the number of PLL lock detections to enable stable and quick search in all bands. .

[Means for solving problems]

The present invention relates to an automatic tuning apparatus for automatically searching for a tuning point by sequentially changing the N value of the frequency division ratio 1 / N of the variable frequency dividing circuit of the local oscillation circuit having the PLL structure. After changing the time, means for setting a predetermined waiting time, means for changing the waiting time according to the reception band, and after the waiting time, PLL lock detection is repeated until a lock is detected with a predetermined number of times as an upper limit. Lock detection means,
Receiving the result of the lock detection means, the tuning point determination means for detecting that it is a tuning point, and the tuning point is detected by the tuning point determination means, and when it is determined that it is a tuning point, the muting of the reception output is released. The auto-tuning device is characterized in that the auto-tuning device is provided with a muting canceling means, and is quickly locked by the lock detecting means.

[Operation] Since the waiting time is changed according to the reception band, the optimum search step speed can be obtained for the reception band, and the lock detection determination is repeated indefinitely by limiting the lock detection means of the PLL. Since it does not occur, a quick search and a reliable tuning point can be obtained.

〔Example〕

FIG. 1 shows an embodiment of the present invention, which is an example for a synthesizer tuner capable of receiving three bands of AM, FM and TV.

In the figure, (10) is a local oscillator circuit, and this local oscillator circuit (10) has a PLL configuration. That is, (1
1) is a variable frequency oscillation circuit (hereinafter referred to as VCO), whose oscillation signal is supplied to a tuner circuit for each band as a local oscillation signal for TV, FM, and AM through a selector (30) and a prescaler. It is supplied to (12) and is divided in advance, and then supplied to a variable frequency dividing circuit (13). The N value of the frequency dividing ratio 1 / N of the variable frequency dividing circuit (13) is given from the microcomputer (20). The output of the variable frequency dividing circuit (13) is supplied to the phase comparison circuit (14) and compared in phase with the reference signal from the reference oscillation circuit (15), and the comparison output is passed through the low pass filter (16) to the VCO ( 11) and the oscillation frequency of the VCO (11) is controlled to a value according to the division ratio 1 / N.

In this case, the microcomputer (20) is designed to perform the auto tuning function. First
(201) to (205) in the figure are functional blocks for performing the auto tuning.

That is, (201) is a search means that starts driving when the search button (21) is pressed, (202) is an N value changing means driven by this search means (201), and (203) is a variable frequency dividing circuit ( With N value supply means for supplying N value to 13),
The N value supply means (203) stores a plurality of N values that can be received within each band at predetermined frequency intervals.
It consists of RAM and its read address means. The N value changing means (202) supplies a command signal to the address means of the N value supplying means (203). Reference numeral (204) is a band detection means, and a signal according to the band selection by the band selection switch (22) is supplied to the band detection means (204) to detect the selected band. Then, a signal corresponding to the detected band is supplied to the N-value changing means (202), whereby the N-value supplying means (203) is controlled so as to output the N value in each band. Further, the output of the band detection means (204) is supplied to the prescaler (12), and the value of the fixed frequency division ratio is switched according to the reception frequency of each band. Further, the output of the band detection means (204) is supplied to the selector (30), and the local oscillation signal is supplied to any one of the tuner circuit for TV, FM, and AM according to the band switching.

Then, when the search button (21) is pressed, the received output is muted and the search means (201) drives the N value changing means (202) to supply the N value supplying means (20).
From 3), the N value is sequentially read in the N value changing step and supplied to the variable frequency dividing circuit (13). In this case, the search button (21) actually has two button switches, an up button and a down button, and when the up button is pressed from the N value supply means (203), the reception frequency is Is sequentially read out, and when the down button is pressed, N values that should be the local oscillation frequency to decrease the reception frequency are sequentially read out.

In the case of this example, the following search cycle is set for one N value, and the presence or absence of broadcast waves is detected within this search cycle period.

That is, FIG. 2 is an explanatory diagram of this search cycle,
When the N value is changed, a wait time of a predetermined time is provided. This is the waiting time set so that the output of the PLL low pass filter (16) is sufficiently stable. When this wait time elapses, the PLL lock detection time is reached, and lock detection is performed about once every 15 msec, for example, about 15 times. If the lock is detected even once within the lock detection time, the presence / absence of the broadcast wave is started to cancel the muting of the reception output. Therefore, for example, when it is determined whether or not the tuning point is the tuning point by rectifying the intermediate frequency carrier, even if there is a delay in the rectification time constant, it is determined whether or not the tuning point is for one N value. Is made sure within that search cycle.

In this case, the wait time can be changed according to the band. That is, in a multi-station band such as an AM band or an FM band, this wait time is set to be relatively short, for example, 90 msec. On the other hand, the wait time is relatively long, for example 210 m, because there are few stations in the TV band (we are considering the VHF band here).
Set to sec.

In FIG. 1, reference numeral (206) is a lock detecting means for detecting whether or not the local oscillation circuit (10) of the PLL configuration is locked, and the detection is performed by detecting the output of the phase comparison circuit (14) within a predetermined range. It depends on whether it is inside or not. A wait means (205) is provided in front of the lock detecting means (206), and the lock detecting operation is performed after the set wait time has elapsed. Here, the wait time is preset according to the band selection by the signal from the band detection means (204). In the case of this example, when the lock is detected, and when the lock cannot be detected, the maximum number of times the lock is detected and the next operation is also performed. It is possible to preset according to the band selection by the signal.

In the case of this example, the maximum number of times of lock detection is 15 times in the TV band and 15 or 30 times in the FM and AM bands.

When the lock detecting means (206) detects the lock even once, a start signal is sent to the tuning point judging means (207) to start judging whether or not the N value is the tuning point. This discrimination means (207)
Is rectified, for example, the intermediate frequency carrier of the tuner for the selected band, and a "1" or "0" signal indicating whether or not the rectified output is at or above a predetermined level is supplied to determine the tuning point. Done.

When the discriminating means (207) discriminates that it is the tuning point, the search means (201) is given an instruction to temporarily stop the change of the N value, and the muting signal generating means (208) outputs the muting signal. The muting signal is changed to a muting cancellation signal, and the reproduced sound is emitted for 5 seconds, for example.

If the N value is not the tuning point, the N value is advanced by one. In addition, lock detection means (20
Even if the maximum number of times of lock detection is performed in 6), but the lock detection is not possible, once the determination operation is performed by the tuning point determination means (not detected as a tuning point), the N value is Will be updated.

FIG. 3 shows an example of a flow chart when the above-mentioned auto tuning search operation is executed by the microcomputer (20).

To explain this flowchart, first, it is determined whether or not the search button (21) is turned on (step [10
1)). If the search button (21) is not turned on, the status of other keys is checked (step [10
2)). At this time, the state of the band selection switch (22) is detected, and the wait time and the maximum number of lock detections are preset according to the selected band.

After checking the status of other keys, step [101]
Return to and repeat the above operation until the search button (21) is turned on.

When the search button (21) is turned on, the N value is changed (step [103]). After this change, the wait time described above is awaited (step [104]), and the PLL lock detection operation starts (step [105]).

When the lock is detected, it is determined whether or not it is the tuning point. In this case, for more reliable determination, the determination as to whether or not this is the tuning point is performed three times (steps [106] to [108]), and muting is performed when it is determined that the tuning point is reached three times in a row. It is canceled (step [109]), so-called sound is output, and then the process returns to step [102]. If the tuning point cannot be determined three consecutive times, the process returns to step [103], and the next N value is updated.

If the lock cannot be detected in step [105], the number of times is counted (step [110]),
While the number of times is less than the set number of times, the lock detection operation is repeated (steps [111] and [105]), and when it is judged that the set number of times is exceeded (step [11]
1)), the process proceeds to step [106], and after the step of detecting whether or not it is the tuning point has elapsed, the value is updated to the next N value.

〔The invention's effect〕

In the present invention, one search cycle is composed of the wait time and the PLL lock detection time, and the wait time is changed according to the number of receiving band stations. A stable tuning point search operation is performed even in a band.

That is, conventionally, in the case of a band with a large number of broadcasting stations,
The time interval for changing the N value should be set relatively short so that the search time from the station with the lowest reception frequency to the station with the highest reception frequency does not become too long. However, when searching for a band with a very small number of other stations with such short time intervals, the search speed was too fast, and stable search could not be performed. On the contrary, if the search speed is adjusted to a band with a very small number of stations and a band with a large number of stations is searched, a problem that the search takes too long occurs, but in the present invention, it depends on the number of stations in the reception band. Since the wait time is changed, if the number of stations is small, the search step will be slow and stable search can be performed. If the number of stations is large, the search step will be quick and quick search will be possible. And after making it possible to search the weight time according to the band in this way,
When the PLL is not locked, the lock discrimination operation is repeated a predetermined number of times, and after that, the mute means is unmuted after the reception tuning point is detected multiple times in succession. , A good output sound is always obtained, and no annoying click sound is output.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of the device of the present invention, FIG. 2 is a diagram for explaining its operation, and FIG. 3 is a flowchart of the operation of an example of the device of the present invention. (10) is a local oscillation circuit having a PLL configuration, (13) is its variable frequency dividing circuit, (20) is a microcomputer, and (202) to (208) are its functional blocks.

Claims (2)

(57) [Claims] 1. An automatic tuning device for automatically searching for a tuning point by sequentially changing the N value of a frequency division ratio 1 / N of a variable frequency divider circuit of a local oscillation circuit having a PLL structure. A means for setting a predetermined waiting time after changing the N value, a means for changing the waiting time according to a reception band, and a lock detection of the PLL after the waiting time with a predetermined set number of times as an upper limit. A lock detecting means that repeats until lock is detected, a tuning point determining means that receives the result of the lock detecting means and detects that it is a tuning point, and a tuning point is detected by the tuning point determining means and a tuning point is detected. An auto-tuning device comprising: a muting canceling means for canceling muting of a reception output when it is determined that there is such a thing, and the lock detecting means locks the muting quickly. 2. The tuning point determining means receives the result of the lock detecting means and determines that the tuning point is a tuning point when a plurality of consecutive predetermined tuning points are detected. The automatic tuning device according to item 1.