JPS60236316A - Channel selection method of television receiver - Google Patents

Abstract

PURPOSE:To accelerate a channel selecting action by confirming the presence of a station detecting signal after detecting the down signal only in a search mode and then the center signal or the up signal. CONSTITUTION:A VCO4 scans the local oscillation frequency by the output of a control circuit 11 during a period when the down signals are detected from an end to the other end of a prescribed set range successively by steps of the prescribed frequency width. The circuit 11 sets the local oscillation frequency sets the local oscillation frequency at a level obtained by adding an offset frequency corresponding to a channel plan to the local oscillation frequency on the channel plan only in case a down signal is not detected first by an AFT wave detecting circuit 8 through the above-mentioned scan. Then the scan is carried out to detect the presence or absence of both the center and up signals through a station detecting signal generating circuit 10 when no down signal is detected any more. Then the circuit 10 detects the presence or absence of a station detecting signal SD when the center or up signal is detected. In this case, the fine tuning is carried out. This can accelerate a channel selecting action.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a channel selection method in a television receiver.

(Technical background of the invention and its problems) AFT (Aut
In order to set the optimum reception frequency using up and down signals and station detection signals from the automatic Fine Tuning (Fine Tuning) means, the tuning device of a television receiver has generally been constructed as shown in FIG.

The signal received from the antenna 1 is amplified by the high frequency amplifier 2, converted to an intermediate frequency by the local oscillation frequency of the VCO 4 and the frequency mixer 3, and amplified by the intermediate frequency amplifier 5.
A video detector 6 obtains a video signal, and a synchronization separation circuit 7 separates the signal into horizontal and vertical synchronization signals.

A video carrier wave is extracted from the video detector 6, passed through a limiter, and then an AFTS curve output is obtained by the AFT detector 8. This S curve output is supplied to the AFT signal generator 9,
The AFT signal generator 9 generates an amplifier signal when the video center frequency is below a predetermined frequency, and generates a down signal when the frequency is above the predetermined frequency. On the other hand, the output of the synchronization separation circuit 7 is supplied to the station detection signal generator 10, and when the station detection signal generator 10 detects the presence of a receiving station, a station detection signal (hereinafter referred to as the SD double signal) is generated. Send.

These up, down signals and SD double signal control circuit 1
1, the presence or absence of a station is determined by the SD double signal, and
If the FT up signal is present, the local oscillation frequency of the VCO 4 is increased, and if the AFT down signal is present, the local oscillation frequency is decreased.

FIG. 3 shows this SD double signal, AFT amplifier, and down signal, and the predetermined value width is set to ±2 MHz. In this figure, the optimum reception frequency range is a period a when the SD double signal is H and both the AFT up and down signals are L, but the period near (α±2) MHz (α: video center frequency) is A similar situation exists in c, where the optimal reception frequency range is sometimes mistaken for period a, and especially when there is an offset from the transmission frequency, it is difficult to receive in the regular reception frequency range period a. . To explain this further, for example, the frequency relationship when receiving three channels of television broadcasting in the United States is as shown in Figure 3, the video frequency [F] is 61.25 MHz and the audio frequency ■ is 65.75 MHz.
MHz, while the local oscillation frequency O8C is 10
If it is 7MHz, the video frequency [F] and the audio frequency■
As shown in Figure 5, [F] is 45.75MHz,
(2) is converted to an intermediate frequency of 41.25 MHz to obtain a 3-channel signal, and the SAW filter shown in the figure extracts only the received 3-channel signal and suppresses other unnecessary channel signals. The AFT detector 8 performs FM detection at the video center frequency of 45.75 MHz, but if the local oscillation frequency is moved above or below 107 MHz, the S-curve of its output changes as shown in FIG. Note that FIG. 6 shows the characteristics when no offset exists in the middle channel of the third channel. At this time, the local oscillation frequency is 107MHz
When , the S curve is at the center, that is, the video carrier is at 45.
When the frequency is adjusted to 75 MHz and the window width shown in FIG. If it is on the lower side of the window side (on the right side of the S curve), a down signal is output to determine whether to amplify or lower the local oscillation frequency. However, due to the band characteristics of the SAW filter, the S-curve is not vertically symmetrical, and the upper frequency (the right side of the S-curve due to the video frequency) becomes narrower, as shown in FIG. 5a. Therefore, in the above-mentioned conventional AFT device that uses only the S curve, the width that can be pulled in by AFT is asymmetrical with respect to the image center frequency, and there is a limit (approximately IMHz) at the upper frequency.

Therefore, in order to eliminate the above-mentioned drawbacks, the applicant has proposed
After the D times signal is detected, the down signal is detected, and then fine tuning is performed to bring it into the center frequency range, and the local oscillation frequency is further lowered by one step, by the frequency fs, and the up signal is detected. Then, increase the local oscillation frequency by 2 steps, increasing the frequency to 2fs.
The local oscillation frequency is increased by one step to confirm that a down signal is detected, and finally the local oscillation frequency is decreased by one step to complete tuning.

However, the above method has the disadvantage that it takes a very long time to complete the channel selection.

This is because it takes several IQmsec to change the local oscillation frequency, confirm the SD multiplied signal, etc.

Furthermore, since it is not possible to select a channel unless the AFT up signal, down signal, and sensor signal are precisely detected, the AFT voltage detection circuit is required to have higher performance, which increases the number of parts.
This method has disadvantages such as increased cost and the need to adjust the AFT curve.

[Purpose of the invention]

The present invention has been made in view of the above, and eliminates the above-mentioned drawbacks, allows quick channel selection, requires a simple and inexpensive circuit for the AFT signal generator, and further reduces the need for AFT curve adjustment. The purpose is to provide a channel selection method.

[Embodiments of the invention]

The present invention will be explained below using examples.

The device to which the method of the present invention is applied has the configuration shown in FIG. 2, and the AFT signal generator 9 is provided with a window of a predetermined width. is set so that it becomes the center output. That is, as shown in FIG. 1al, the AFT signal generator 9 outputs an AFT up signal (hereinafter simply referred to as amplifier output), an AF, T down signal (hereinafter simply referred to as down output), an amplifier output, and a down output. The center output between
It is set to correspond to -6N.

The amplifier output, center output, and down output output from the AFT signal generator 9 and the station detection signal (SD double signal) output from the station detection signal generator 10 are supplied to the control circuit 11 and are The presence or absence of four types of signals is detected and compared to set the oscillation frequency of the local oscillator 4.

The operation of the control circuit 11 is as shown in the flowchart of FIG. 1(b). When you start tuning, the local oscillation frequency is set to the local oscillation frequency +(f'N+fc)/
2 (step ao).

Following step 21H, it is detected whether there is a down output (step a). Here, the presence of the down output is detected first because the amplifier output may be present even when no station is present, and the down output is always present when the station is present. .

In step a, when a down output is detected, the local oscillation frequency is lowered by two steps (2fs) (step b), and it is detected whether it is within the search range (step C). Here, fs is set to fs<f'H. When the down output is not detected in step a, it is determined whether the down output is detected for the first time in step a (step do), and if it is detected that the down output is detected for the first time in step dO, the local oscillation frequency is The local oscillation frequency on the channel plan - (1
, 25MHz - 2 step frequency), step d1), and set the local oscillation frequency to 1 for step d1.
It is increased by a step (step knob d), and it is detected whether it is within the search range (step e). the first in step do
When it is detected that it is not the first detection, step dO
Subsequently, step d is executed. If it is detected in step e that the frequency is outside the range of -1,000, the local oscillation frequency is set to the lower limit of the search range (step f), then step a is executed, and in step e it is detected that the frequency is within the search range. Then step a is executed following step e.

Therefore, in steps a, d, e, and f, the local oscillation frequency is increased by one step (fs) from the lower side of the search range until a down signal is detected. When the upper limit of the search range is reached, the search starts from the lower limit of the search range and is repeated until a down signal is detected.

When it is detected that it is outside the search range in step C, the local oscillation frequency is increased by 1 from the local oscillation frequency when the down output is detected for the first time.
Step (fs) Increase local oscillation frequency Step g
), it is detected whether it is within the search range (step h).

When it is detected in step h that the search range is within the search range, step a is executed following step h. Further, when it is detected in step h that the search range is outside, step f is executed subsequent to step h.

If it is detected in step C that it is within the search range, detect the presence of down output (step i)
. When a down output is detected in step i, step b is executed. When the down output is detected in step i, it is detected that the center output is detected (
Step j).

Therefore, by steps a, b9g, h, and i, when the down output is detected, the local oscillation frequency is increased by two steps (2f) until the center output or up output is found.
If the down output is not found to the lower limit of the search range, step d, e, f, a is performed again from the local oscillation frequency when the down output is detected and the local oscillation frequency starts to be lowered. will be repeated.

When the center output is detected in step j, subsequent to step j, it is detected whether the SD double signal is present (step l). If the center output is not detected in step j, the local oscillation frequency is increased by one step (step k), and then step! Execute.

If the SD double signal is not detected in step l, step g is executed. When the SD double signal is detected in step l, the presence of the up output is detected following step e (step m).

Furthermore, step 7 is determined by l, esk and l to determine the center output or amplifier output (in step distortion, if the down output is not detected and the center output is not detected in step j, then the amplifier output is present). ) exists, and if the up output exists, increase the local oscillation frequency by one step (fs), and if the center output or up output exists, check the existence of the SD double signal. However, when the SD double signal exists, it means that there is a broadcast, and the search is terminated. Next, fine tuning in a frequency width fr narrower than one step is performed in steps m to S to be described later.

When the up signal is detected in step m, the local oscillation frequency is increased by the frequency f (step n) following step m. Here, the frequency fr is a frequency width smaller than the frequency for one step of the local oscillation frequency. Yes, fine tuning is performed.Subsequent to step n, it is detected whether it is within the hold range (step 0).

When it is detected in step 0 that it is outside the hold range, step f is executed, and when it is detected in step O that it is within the hold range, it is detected whether the SD double signal is present (step p).

If the up output is not detected in step m, it is detected whether the down output is detected (step q). When a down output is detected in step q, the local oscillation frequency is decreased by the frequency fF following step q (step r), and it is subsequently detected whether it is within the hold range (step S). If it is detected in step S that it is outside the hold range, step f is executed following step S. When it is detected in step S that it is within the hold range, and when no down output is detected in step q, step p is executed. When the SD multiplied signal is detected in step p, step m is executed, and when the SD multiplied signal is not detected, step f is executed.

In other words, in fine tuning, for example, when a down output is detected, the local oscillation frequency is lowered in steps of frequency fF until the center output is detected, and when an up output is detected, the local oscillation frequency is lowered in steps of frequency fF. The local oscillation frequency is increased until the desired station is detected, and while the desired station is being received, step m → step n-4 step 〇-step p-step m or step m
-" Step q (→ Step r - Step S) - Step P - Step m are processed in a loop. Also, if the local oscillation frequency exceeds the hold range or S
When the D-fold signal is no longer detected, the search is started again from the lower limit of the search range.

Further, many of the HRC signals of US CATV are offset by -1°25 MHz on the local oscillation frequency with respect to on-air or standard signals. For this reason, steps do and dl are provided as described above, and the local oscillation frequency is not set as the search lower limit only during the first search, and the local oscillation frequency on the channel plan - (1,25MHz - frequency for 2 steps) is set. In order to search by setting the local oscillation frequency in You will be able to receive it within the specified time.

On the other hand, +750 on the local oscillation frequency of the HRC signal.
For a signal offset by KHz, the image is moved from the smear side to the reception direction, so there is no image disturbance. - Although the above-described embodiment of the present invention has been described with respect to a television receiver, the present invention can also be applied to PLL synthesizer tuners in general.

Furthermore, although the present invention has been described in the case of the upper local oscillation frequency, the direction of frequency change in the above embodiment may be reversed also in the case of the lower local oscillation frequency.

Further, it is not restricted by the system of the television receiver.

In addition, in the above embodiment, only during the first search, the local oscillation frequency was set to the local oscillation frequency on the channel plan - 0.25MHz (frequency corresponding to 2-2 steps). This is to ensure that the local oscillation frequency is set in the DOWN output region in Figure 1 (al, that is, the frequency range fDN), so in the first search, "Local oscillation frequency on the channel plan - (1,25MH! - 2 steps of frequency)" to [Local oscillation frequency on the channel plan - (1, 25 MHz
-(f c+f DN)/2)J. Furthermore, the same effect can be obtained by using an appropriate value for 1.25 MHz according to the channel plan of the country in which it is used.

〔Effect of the invention〕

As explained above, according to the present invention, when searching, only the down output is detected, then the center output or the up output is detected, and then the search is completed by confirming the presence of the SD double signal, so that the channel selection operation is quick. It will be done. Furthermore, after detecting the down output, it is sufficient to detect either the center output or the up output, so there is no requirement for strictness in the up output, center output, and down output. Therefore, the AFT signal generator is simple and inexpensive. Furthermore, since the amplifier output, center output, and down output are not required to be precise, adjustment of the AFT curve is not required.

Furthermore, the time required to receive a broadcast of a frequency that is offset to a certain value is shortened, and image disturbances can be reduced.

[Brief explanation of drawings]

FIG. 1 (al is a diagram showing an AFT curve of an AFT signal generator in an embodiment of the present invention, FIG. 1 (bl is a flowchart showing an embodiment of a channel selection method according to the present invention, and FIG. 2 is a conventional FIG. 3 is a block diagram showing the configuration of a channel selection device capable of performing a channel selection operation according to the present invention; FIG. 3 is a diagram showing a station detection signal, amplifier output, and down output for explaining a conventional channel selection method; The figure shows an example of the video and audio frequencies of a broadcasting station, Figure 5 shows the frequency when the station frequency in Figure 4 is frequency converted, and Figure 6 shows the video and audio frequencies in Figures 3 and 4. It is a diagram showing the detection output of an audio signal. 6...Video detector, 7. Old...Synchronization m circuit,
8...AFT detector, 9th...AFT signal generator, 1゜...station detection signal generator, 11...
...control circuit. Patent applicant Pioneer Co., Ltd. dMHz Fourth cause O8C*I07MHz

Claims (1)

[Claims] The AFT voltage is set to fall within a window for a received signal without an offset, a center signal is output for a signal within this window, a down signal is output for a signal exceeding the center signal, and a center signal is output for a signal that exceeds the center signal. In a channel selection method for a television receiver equipped with an AFT signal generator that outputs an up signal for a signal that is less than a signal, and a station detection signal generator that outputs a station detection signal that detects the presence of broadcasting,
Set the local oscillation frequency.Scan from one end of the predetermined range to the other end in steps of a predetermined frequency width during the period in which a down signal is detected, and in this scanning, the first down signal is detected when the first down signal is detected. Only when the down signal is not detected, set the local oscillation frequency to the local oscillation frequency on the channel plan plus the offset frequency corresponding to the channel plan, perform the above scanning, and when the down signal is no longer detected, the center signal and up signal are set. A television receiver characterized in that it detects the presence or absence of a station detection signal when either a center signal or an amplifier signal is detected, and enters fine tuning when the station detection signal is detected. How to select channels.