JPH077391A - Auto search tuning system - Google Patents

Abstract

PURPOSE:To constitute the system in such a way that only a desired channel can be received automatically without being influenced by input electric field intensity and also, even if a signal receiving state is complicated. CONSTITUTION:By varying automatically a tuning voltage impressed to a variable capacity diode of a local oscillation circuit of a tuner 1, a tuning point is determined automatically, based on a synchronizing signal of a received television signal and an AFT signal. Plural reference values for deciding whether the synchronizing signal exists or not are prepared in advance in a channel selection microcomputer 5, and one of them can be selected by operating a reference value switching key 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a television receiver and a V receiver.
The present invention relates to an auto search tuning system used in TR and the like.

[0002]

2. Description of the Related Art For example, in a television receiver, a channel which can be received at a place where the television receiver is installed is automatically set by simply pressing an auto search tuning key. At this time, when the tuning voltage applied to the variable capacitance diode of the local oscillation circuit of the tuner is changing and a tuning signal is obtained, the tuning voltage value is stored in the memory in association with the channel number. Then, as the tuning signal, the detection output of the horizontal synchronizing signal and the AFT signal are usually used.

The detection output of the synchronization signal is taken into a tuning microcomputer (hereinafter referred to as "tuning microcomputer"), compared with a reference value by a comparator in the tuning microcomputer, and when the reference value is exceeded, synchronization is performed. It is determined that there is a signal. In this case, the conventional auto search tuning system uses a general I / O port or uses an external comparator, so that the reference value is fixed.

[0004]

Conventionally, since the reference value for determining the synchronization signal is fixed in this way, when the reference value is set low, a building co-listening reception system in which the ON AIR broadcast signal is RF-converted is adopted. Where there is a building co-listening broadcast channel with a high signal level and ON with a low signal level
There has been a problem that both of the AIR broadcast channels are stored in the memory. On the contrary, when the reference value was set high, the automatic search did not stop in the weak electric field area and the desired channel could not be received.

The present invention has been made in view of the above circumstances, and is an automatic search tuning system which is not affected by the input electric field strength and can automatically receive only a desired channel even if the signal receiving state is complicated. The purpose is to provide.

[0006]

In order to achieve the above object, according to the present invention, the tuning voltage applied to the variable capacitance diode of the local oscillation circuit of the tuner is automatically changed to obtain the synchronizing signal of the received television signal and the AFT. In an auto search tuning system that automatically determines a tuning point based on a signal, a plurality of reference values for determining the presence or absence of the synchronization signal are prepared in advance, and one of them can be selected by operating an operating member. There is.

[0007]

With this structure, the reference value for determining the presence / absence of the synchronization signal can be selected according to the radio wave condition.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is a tuner, 2 is a video / audio IF circuit, 3 is a video / chroma processing circuit, 4 is a sync signal detection circuit, 5 is a channel selection microcomputer, and 6 is a memory. The sync signal detection circuit 4 is composed of a sync separation circuit, a horizontal pulse gate circuit, and an integration circuit. An operation panel 7 includes a reference value switching key 8 and an auto search key 9.

Before the automatic search tuning is started by operating the automatic search key 9, the user selects an appropriate one of the three reference values for synchronization judgment by the reference value switching key 8 in accordance with the reception condition. By this selection, the tuning microcomputer 5 sets the reference value. still,
Each time the reference value switching key 8 is pressed, a high, medium, or low reference value is cyclically selected. The selected reference value is supplied to the inverting terminal (−) of the comparator 10 shown in FIG.
The non-inverting terminal (+) of the comparator 10 is supplied with a DC voltage according to the level of the sync signal from the sync signal detection circuit 4. The comparator 10 is provided in the channel selection microcomputer 5, and specifically, the value digitized by the A / D converter is compared with a reference value controlled by software.

Next, the operation of the automatic search tuning will be described with reference to the flowchart of FIG. When the key 9 is operated and the auto search command is received thereby, the tuning microcomputer 5 reads the reference value selected by the user with the key 8 from the memory 6 and outputs it to the comparator 10.
(# 5). Then, the channel number is set to 1 (# 10), the tuning voltage and the band switching data are supplied to the tuner 1 to start the automatic search (# 1).
5).

In this embodiment, the tuning voltage is increased from the lower limit of the tuning voltage variable range at this time. Then, in steps # 20 to # 35, the subroutines shown in FIGS. 4 to 7 are sequentially executed. First, in the subroutine, in step # 100, the sync signal (in this case, a direct current) from the sync signal detection circuit 4 is input,
In the next step # 105, it is determined whether the value is larger than the reference value. If it is larger than the reference value, the process proceeds to step # 110 to input the AFT voltage, and it is determined in step # 115 whether or not the AFT up signal is present. Here, the AFT up signal refers to a portion exceeding the level Eu in FIG. 8, and the AFT down signal described later refers to a portion exceeding the level Ed downward.

If there is an AFT up signal in step # 115, the process returns in step # 120. If the sync signal is below the reference value in step # 105,
The process proceeds to step # 125, and AF is performed in step # 115.
Even if the T-up signal is not detected, step # 125
Then, it is determined whether each tuning voltage exceeds the upper limit. If the tuning voltage exceeds the upper limit, step #
In 135, it is determined whether or not it is the upper limit of UHF, and if so, the automatic search is stopped in step # 145. If it is less than the upper limit in step # 125, the process proceeds to step # 130, the tuning voltage is further increased, and the process returns to step # 100. If it is not the upper limit of UHF in step # 135, band switching is performed in step # 140 and then step # 100.
Return to.

Next, the sub-routine is based on the above-mentioned sub-routine, and the difference is that the presence or absence of the AFT down signal is determined in step # 215. Therefore, detailed description of the subroutine is omitted.

At the time of entering the next subroutine, the automatic search has reached point (c) in FIG.
In the subroutine, first, in step # 300, the counter in the channel selection microcomputer 5 is reset to 0, and then, in step # 305, the synchronization signal is input, and in step # 310, whether the synchronization signal is larger than the reference value or not. Determine whether or not.

If the sync signal is below the reference value,
Return to step # 100 of the subroutine. If the sync signal exceeds the reference value, the AFT voltage is input in step # 315, and the presence or absence of the AFT up signal is determined in the next step # 320. If there is no AFT up signal, step #
The process proceeds to step 325 to decrease the tuning voltage, the counter is incremented in step # 335, and the process returns to step # 305. This means that the search returns from the point (c) to the direction (b). Then, when the point (a) is reached, the determination result of step # 320 is YES, and the subroutine is executed.

In the subroutine, the AFT voltage is input in step # 400, and in step # 405, the tuning voltage is increased to the tuning voltage corresponding to the half of the count value of the counter, that is, point (b). Then, in step # 410, the sync signal is input, and after it is confirmed that the sync signal exceeds the reference value, the process returns. If it exceeds, the process returns to step # 100 of the subroutine.

Now, when returning at step # 420, the tuning voltage is written in the memory 6 in correspondence with the channel number 1 in step # 40 of the main routine (FIG. 3). After that, increase the channel number to 2 (# 4
(5,) and the tuning voltage is also increased (50) and the process returns to the subroutine to perform an automatic search for channel number 2. In the same manner, the automatic search and the tuning voltage storage are similarly performed for all channels.

The automatic search tuning according to the above description is a case in which the tuning (tuning) determination is performed using only the synchronization signal. However, as will be described below, the RFAGC voltage and the IFAGC voltage are also added in addition to the synchronization signal. By performing the tuning determination by performing the tuning determination, it is possible to realize more accurate and preferable auto search tuning. This is because the output of the synchronization signal detection circuit 4 does not change unless the electric field strength becomes low, and the change in the electric field strength cannot be detected with high accuracy. The output of the sync signal detection circuit may be sufficient if it is about two divisions of high and low, but when the division is three or more (high, middle, low), the RFAGC
By using the voltage and the IFAGC voltage, the change in the electric field strength can be properly and accurately grasped, so that it becomes easy to match the desired division set electric field strength point.

Now, as one form of the auto search tuning system which takes such AGC voltage into consideration, the RF AGC and IF AGC voltages are applied to the I / O port of the microcomputer 5 (I / O to which the sync signal detection output is inputted). It is configured to be input to another I / O port different from the port) and to be compared with the reference level. Then, an auto search is performed using the output of the sync signal detection circuit 4 described above. When the auto search is stopped, RFAGC and IFAG
The final tuning determination is performed by also considering the output of the comparison result with the reference value of the C voltage.

The reference voltage for comparing RFAGC and IFAGC can also be switched in three steps in the same manner as the reference voltage for comparison of the sync signal detection output.
When C is a forward type AGC, the reference voltage for synchronizing signal detection output is set to high, medium, and low as compared to high, medium, and low, but in the case of a reverse type AGC, low, medium, and high. Shall be switched to have the opposite relationship.

Unlike this form, the sync signal detection output and the RFAGC and IFAGC voltages are preliminarily superimposed and input to one I / O port of the microcomputer 5, and the input is compared with the reference voltage. Good. Also in this case, the reference voltage can be switched in a plurality of steps. In this form,
In the case of a reverse type AGC, it is passed through an inverter and then superposed on the sync signal detection output.

[0022]

As described above, according to the present invention, the reference value for determining the presence / absence of the sync signal can be selected according to the radio wave condition. Where an audio receiving system is used, by raising the reference value, it is possible to select only the building co-listening broadcast channel with a high signal level, and select the ON AIR broadcast channel with a low signal level. This problem is avoided. In addition, by selecting a low reference value in a weak electric field area, all desired channels can be received.

[Brief description of drawings]

FIG. 1 is a block diagram of an auto search tuning system embodying the present invention.

FIG. 2 is an equivalent circuit diagram showing a part of the configuration thereof.

FIG. 3 is a main flowchart of an auto search operation.

FIG. 4 is a flowchart of the subroutine.

FIG. 5 is a flowchart of the subroutine.

FIG. 6 is a flowchart of the subroutine.

FIG. 7 is a flowchart of the subroutine.

FIG. 8 is an explanatory diagram regarding an AFT signal.

[Explanation of symbols]

 1 Tuner 4 Synchronous signal detection circuit 5 Tuning microcomputer 6 Memory 8 Reference value switching key 9 Auto search key 10 Comparator

Claims (3)

[Claims] 1. An auto search tuning system in which a tuning voltage applied to a variable-capacitance diode of a local oscillation circuit of a tuner is automatically varied to automatically determine a tuning point based on a synchronizing signal of a received television signal and an AFT signal. In the automatic search tuning system, a plurality of reference values for determining the presence or absence of the synchronization signal are prepared in advance, and one of them can be selected by operating an operating member. 2. The automatic search according to claim 1, wherein the determination is performed by a microcomputer, and the reference value can be switched and set by software of the microcomputer. Tuning system. 3. The result of comparing the RFAGC voltage and the IFAGC voltage with another reference voltage is used for determining a tuning point, and a plurality of the other reference voltages are prepared so that one of them can be selected. The automatic search tuning system according to claim 1, wherein: