JPH03110916A - Broadcast receiver - Google Patents

Abstract

PURPOSE:To reduce an IF output fluctuation and to reduce disturbance of pattern at picture output by stopping a tuning voltage nearly at the center voltage of a changing range in the case of band changeover in the automatic search, and transferring the voltage to a voltage corresponding to a channel in the order of search. CONSTITUTION:A channel selection microcomputer circuit 4 references a synchronizing detection signal from a video intermediate frequency detection circuit 3 at the time of automatic searching and executes channel search automatically for a signal presence channel. Then in the case of channel transfer between a VH band and a UHF band, the tuning voltage is tentatively stopped at a voltage V0 nearly between a voltage V1 corresponding to the final channel before the transit and a voltage V2 corresponding to the initial channel of the search at the UHF band after the transit. Then the voltage is changed to the voltage V2 to decrease one voltage change in comparison with case with direct change from the voltage V1 to V2. Thus, the voltage response is remarkably improved and the voltage change in the transit to the voltage V2 is made stable for a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to an improvement in a broadcast receiving apparatus that can locate a station using an automatic search function for signaled channels.

(Prior Art) FIG. 3 shows an outline of a receiving device having an automatic search function in a TV receiver.

In FIG. 3, a channel of a desired band is selected from a signal induced in an antenna 1 by an electronic tuning tuner 2. The F ratio output of the electronic tuning tuner 2 is subjected to signal gain control t (IFAGC) and image detection by a video intermediate frequency detection circuit (hereinafter referred to as PIF detection circuit) 3.

Reference numeral 4 denotes a tuning microcomputer circuit for controlling the tuning of the electronic tuner 2. The channel selection microcomputer circuit 4 is coupled to a key input circuit 5 such as a remote control keypad, and is also connected to a channel data ROM containing frequency data and band data for receiving TV channels.

The channel selection microcomputer circuit 4 generates frequency and band data of a desired channel in response to a channel selection command from the key input circuit 5. Band data is Vl-I
F high band (VH), low band (VL) and U
Switch to HF. These frequency and band data are P
The voltage is supplied to the LL tuning circuit 7, and the PLL tuning circuit 7 forms a band switching voltage and a tuning voltage corresponding to the desired channel.

Further, the channel selection microcomputer circuit 4 is supplied with a synchronization detection signal output from the PIF detection circuit 3. The synchronization detection signal is a signal indicating the presence or absence of a synchronization signal in the video detection output, and this signal allows the channel selection microcomputer circuit 4 to detect the presence or absence of a broadcast signal of the channel received by the electronic tuner 2.

8.9 is a video mute circuit and an audio mute circuit that mute video and audio when switching channels;
The mute signal is supplied from the channel selection microcomputer circuit 4.

In addition to the normal channel selection mode, the broadcast receiving apparatus described above has an automatic search mode in which it searches for the presence or absence of a broadcast signal and automatically searches for a channel with a signal.

The automatic search mode is switched to when a predetermined key is pressed in the key input circuit 5. In the automatic search mode, the channel selection microcomputer circuit 4 searches the table in the channel data ROM 6 in the order of channel numbers. To determine the signaled channel, the search is stopped in response to a synchronization detection signal from the PIF detection circuit 3. During the search, a mute signal is generated and both video and audio are muted.

The numerical table shows an example of searching channels including European CATV broadcasting.From the right column, search order channel NAM
E represents the frequency (local oscillation frequency) and band.

FIG. 4 shows the tuning voltage button curve when automatically searched according to the frequencies shown in Table 1 below.

In FIG. 4, the vertical axis represents the tuning voltage, and the horizontal axis represents the search channel. The tuning voltage remains constant for a certain period of time and changes stepwise, corresponding to the channel. During this period, the channel selection microcomputer circuit 4 judges whether or not synchronization is detected from the PIF detection circuit 3.

Automatic sweep is stopped when a signaled channel is detected.

Here, if we compare the tuning voltage when moving from the vH band to the LIHF band and the tuning voltage when moving from the %VL band to below the VH pan, we can see that in the latter case, the change in tuning voltage is less than 5 [■]. For,
In the former case, it changes to near 30 [Vl. When the tuning changes are large like this, the response time becomes longer and image output is delayed. In addition, due to such a rapid change, it takes time for the tuning voltage to stabilize, and the IF ratio output of the electronic tuning tuner 2 fluctuates, making it impossible for the AGC response of the PIF detection circuit 3 to follow up, resulting in the rise of the image. There is an inconvenience that it gets messy.

(Problems to be Solved by the Invention) As described above, when changing channels accompanied by band switching during automatic search, there is a sudden change in the tuning voltage, which delays image output and Due to small output fluctuations, the AGC response of the PIF detection circuit 3 cannot follow,
There was a problem that the screen was distorted when the image was output.

It is an object of the present invention to provide a broadcast receiving apparatus which eliminates the above-mentioned problems and eliminates delays and disturbances in displaying images during automatic search.

[Structure of the Invention] (Means for Solving One Problem) The present invention provides an electronically tuned tuner that receives a predetermined channel of a predetermined band using a band switching voltage and a tuning voltage, detects the iE output from this tuner, and detects the iE output from the tuner, and It has a detection circuit that outputs a detection signal to detect the presence or absence of a low-power broadcast signal, and an automatic search mode that uses the detection signal to search for signal channels. The tuning control circuit includes a tuning control circuit that temporarily stops the tuning voltage at a voltage corresponding to the final channel in the band before the transition, a voltage corresponding to the initial channel in the band after the transition, and a voltage in the middle of opening when changing channels. .

(Function) According to such a configuration, when band switching is performed in automatic search, the tuning voltage stops at approximately the center voltage of the change range, and then shifts to the voltage corresponding to the channel based on the search order. . Therefore, voltage changes during channel switching between bands are reduced, resulting in better response. This reduces IF output fluctuations and reduces screen disturbances during image output.

(Example) Hereinafter, the present invention will be explained in detail with reference to illustrated examples.

FIG. 1 is a block diagram showing an embodiment of a broadcast receiving apparatus according to the present invention, and elements common to those in FIG. 3 are given the same reference numerals.

In Fig. 1, 1 is an antenna, 2 is an electronic tuning tuner, 3 is a PIF detection circuit, 4 is a tuning microcomputer, 5 is a key input circuit, 6 is a channel data ROM, 7 is a PLL tuning circuit, and 8.9 is a PLL tuning circuit. They are respectively video and audio mute circuits, and as in the case of FIG. In addition, at the time of automatic search, the synchronization detection signal from the PIF detection circuit 3 is referred to to automatically locate a channel with a signal. When no signal channel is detected, the video and audio mute circuits 8 and 9 are turned off by the mute signal.
li control to mute video detection and audio intercarrier output.

In this embodiment, in the automatic search mode described above, when a channel is shifted between the VH band and the UHF band, the tuning voltage is set to a voltage corresponding to the last channel of the search in the band before the shift (herein referred to as the VH band). (vl) and the voltage (vl) corresponding to the initial channel of the search in the LJ HF band after transition, it is temporarily stopped at a voltage Vo that is approximately halfway between the voltage (vl), and then automatically sweeps from the voltage (vl) corresponding to the above initial channel. (See inside the square box).

FIG. 2 shows a tuning voltage sweep waveform when automatically searching the European TV channels shown in Table 1.

For European TV channels, when searching from the low band to the high band side, and from the low channel to the high channel side in the same band, the last channel of the vH band is 5201, and the first Ill channel of the UHF band is U21.
It is. Assuming that the voltages corresponding to these channels are V1' and V2, respectively, the substantially intermediate voltage Vo becomes the voltage corresponding to the U46 channel.

Therefore, during automatic search, when switching the channels mentioned above, by temporarily stopping the Vo't%f pressure change from voltage 1 and then changing it to V2, it is easier to change it once from vl to vl than when changing from vl to vl. Voltage changes will be smaller. When the voltage change is small, the voltage response is significantly improved and vl
The voltage change when changing to V2 stabilizes in a shorter time than when changing to V2 at - degrees. Therefore, small IF output fluctuations are small, the AGC response after PIF detection can be sufficiently followed, and the rise of image output is good and stable.

Table 2 shows a channel data table when the above tuning voltage is formed.

Table 2 Note that when stopping at the center voltage Vo, if channel U46 is broadcasting, the signal of the same channel is received, but at this time, muting is applied. This allows searching in a predetermined order.

In the above embodiment, the tuning voltage is changed from a low voltage to a lightning voltage, but the same applies to the case where a search is performed using a tuning voltage that changes from a high voltage to a low voltage. Further, the 3f1 station system is not limited to the PLL frequency synthesizer system, but can also be applied to the voltage synthesis system.

[Effects of the Invention] As explained above, according to the present invention, the tuning voltage does not suddenly change during automatic search, and the PIF
This has the effect that the AGC response of the detection stage is improved, and the time and stability required for image output when detecting a signal-present channel are improved.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a broadcast receiving device according to the present invention, FIG. 2 is a waveform diagram showing a tuning voltage sweep waveform during automatic search according to the present invention, and FIG. 3 is a conventional broadcast receiving device. FIG. 4 is a configuration diagram showing the device, and is a waveform diagram showing a conventional tuning voltage n-subtraction waveform. 1... Antenna, 2... Electronic tuning tuner, 3...
・Video intermediate frequency detection circuit, 4...Tuition selection microcomputer circuit,
5...Key input circuit, 6...Channel data RO
M17...PLL channel selection circuit, 8...Video mute circuit, 9...Sound mute circuit.

Claims (1)

[Claims] An electronically tuned tuner that receives a predetermined channel of a predetermined band using a band switching voltage and a tuning voltage;
It has a detection circuit that outputs a detection signal that detects the presence or absence of a broadcast signal from the F output, and an automatic search mode that searches for signal channels using the detection signal. Broadcasting having a tuning control circuit that temporarily stops the tuning voltage at a voltage approximately halfway between the voltage corresponding to the final channel in the band before the transition and the voltage corresponding to the initial channel in the band after the transition when changing channels. Receiving device.