JP2527557B2 - Tuning circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a television tuning circuit using an electronic tuning tuner.

[Conventional technology]

The electronic tuning tuner is a low band (1ch ~ when receiving VHF band
3ch) and high band (4ch ~ 12ch) need to be switched.

Conventionally, as shown in FIG. 4, a variable resistor 41 is used to generate a tuning voltage, and a switch 42 linked to the variable resistor 41 is used to generate a low band / high band switching signal. Was used.

This switch 42 has a structure that switches during rotation, and by adjusting the switch so that it switches when it reaches the midpoint of 3ch and 4ch, you can automatically turn the knob from 1ch to 12ch by turning the knob. Band switching is performed.

Further, reception of the UHF band is performed by operating the VHF / UHF selector switch 47.

Here, the semi-fixed resistors 43 to 46 set the tuning voltage range for each band. First, the upper frequencies of the VHF high band and the UHF are set by the semi-fixed resistor 43. Second, the lower limit frequency of UHF is set by the semi-fixed resistor 44. Thirdly, the lower limit frequency of the VHF high band is set by the semi-fixed resistor 45. Finally, the upper limit frequency of the VHF low band is set by the semi-fixed resistor 46.

[Problems to be solved by the invention]

However, since the tuning voltage generation circuit of the television using the conventional electronic tuning tuner generates the tuning voltage and switches between low band and high band by mechanical contacts, it is easy to cause fluctuations in contact resistance and poor contact. There was a problem of short life.

Further, a pulley and a thread are required to reduce the speed of the variable resistor with a switch and the knob, and a complicated structure and space are required, which hinders downsizing of the portable television.

Further, since the resistance value of the variable resistor varies greatly, it is necessary to adjust the tuning voltage range for each band.

Further, recent electronic devices tend to prefer feather touch buttons rather than knob adjustments.

Therefore, the present invention solves such a problem,
The purpose is to perform channel selection operation and VHF low band / high band automatic switching by the button operation of feather touch, and to make adjustment of tuning voltage range setting for each band, stable operation and long life , Providing a tuning voltage generation circuit for a television suitable for miniaturization.

[Means for solving problems]

The tuning circuit of the present invention includes a clock generation circuit that generates a clock signal, a counter that performs a counting operation based on the clock signal, and a D / A converter that converts a count value output from the counter into a tuning voltage. An electronic tuning tuner that performs tuning based on the tuning voltage, a tuning button for tuning a desired channel, and a tuning detection circuit that detects that the electronic tuning tuner is tuned and outputs a tuning detection signal. When the tuning button is pressed and when the tuning detection signal is not output from the tuning detection circuit, the clock signal is supplied to the counter, and the tuning detection signal is output from the tuning detection circuit. If it is output and the tuning button is not pressed,
A control circuit for stopping the supply of the clock signal to the counter.

[Action]

Since the present invention has the above configuration, the tuning operation is performed by pressing the tuning button of the feather touch. Also, the output value of the tuning voltage generation counter is VH below a certain value.
The V low band / high band of the tuner is automatically switched by the output of the circuit that determines whether the output value is larger or smaller than this set value while the F low band and the higher band are assigned to the high band.

In addition, the tuning voltage range for each band can be set without adjustment because the output of the D / A converter is amplified and level-shifted by the operational amplifier.

In addition, since the tuning voltage is generated electrically and the band is switched, stable operation is guaranteed for a long period of time, IC is easy, and it is suitable for downsizing of TV.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples.

FIG. 1 is a block diagram of a tuning voltage generating circuit of a television of the present invention, FIG. 2 is a concrete circuit diagram of a tuning voltage switching circuit portion of FIG. 1, and FIG. 3 is a circuit diagram of FIG. 1 and FIG. It is a timing chart figure which shows operation.

It is assumed that all the outputs of the up / down counter 8 are "0" and the channel selection is stopped. If the channel up button 6 is kept pressed, the channel selection is started and the up channel selection clock 17 outputs the up channel selection clock 17. However, while button 6 is being pressed, clock 17 does not stop even if a station is received. Therefore, the up / down counter 8 continues counting up,
The output voltage of the D / A converter 9 rises corresponding to this digital output value. When all the outputs of the up / down counter 8 reach the state of "1", the output voltage of the D / A converter 9 reaches the maximum value, and when the up channel selection clock 17 continues, all the outputs of the counter 8 are again "0". Return to the state of
The output voltage of the D / A converter 9 also becomes the minimum value.

On the other hand, the numerical judgment circuit 10 decodes the upper 3 bits of the counter 8 and outputs "0" during the 3 states from 000 to 010 and outputs "1" during the 5 states from 011 to 111. This output is given to the electronic tuning tuner 2 as a V _L / V _H switching signal 13 for switching between VHF low band and high band. Therefore, in the embodiment, the output voltage range of the D / A converter 9 is divided into 3 to 5 and assigned to the VHF low band and the high band, but this ratio changes the configuration of the gate of the numerical judgment circuit 10. Can be set to any value.

Further, the _VL / _VH switching signal 13 and the VHF / UHF switching signal 16 are input to the tuning voltage switching circuit 11, and only the switch SW3 is turned on when VHF low band is selected. Therefore, in order to obtain the required voltage range, the gain is set by the resistor R3 and the level is shifted by the voltage V3.

Next, when VHF high band is selected, only switch SW2 is turned on. When changing from 3ch to 4ch, a voltage as low as that of 1ch is required again, and the tuning voltage to frequency conversion gain of the tuner 2 increases. Therefore, to prevent the channel display scale interval from becoming narrower for the VHF low band, the resistance R2
The gain is reduced by and the level shift amount is adjusted by the voltage V2.

Further, there is a time constant in the tuning detection, and if the tuning voltage-to-frequency conversion gain rises, the tuning speed is increased, and the tuning detection is performed after jumping over the station. Therefore, in order to match the VHF high band tuning speed to the VHF low band, the resistance R
Gain adjustment by 2 is required.

Next, when UHF is selected, only the switch SW1 is turned on. UH
Since the F tuning voltage range is wider than VHF and the tuning voltage-to-frequency conversion gain is also high, adjustment by the resistor R1 and the voltage V1 is necessary.

As described above, the optimum tuning voltage 14 for each band is generated by the tuning voltage switching circuit 11 and applied to the electronic tuning tuner 2.

Next, when the channel up button 6 is released, the tuning detection circuit 3 is turned on when tuning to the station and the automatic tuning control circuit 5 is reset. Therefore, up tuning clock
17 stops, and the tuning operation ends. Here, as one method of detecting the tuning, an automatic frequency adjustment signal (AFT signal) having an S-shaped characteristic is detected in the vicinity of the station by detecting a tuning deviation from the IF signal output from the electronic tuning tuner 2, and this signal is predetermined. It suffices to detect that the high and low levels of are passed. Furthermore, in order to determine whether or not it is a television signal, the presence or absence of a motive signal is detected and added to the synchronization determination, which is complete.

The channel selection in the down direction is performed in the same manner by pressing the channel down button 7.

Further, in the embodiment, the case where the tuning detection circuit 3 is provided and the tuning is stopped automatically is shown, but if the tuning detection circuit is deleted, the manual tuning in which the tuning state is maintained only while the button is pressed is also possible. is there.

〔The invention's effect〕

As described above, according to the present invention, even when the electronic tuning tuner tunes to an undesired station, the counter continues counting by pressing the tuning button, so the desired station can be selected while performing automatic tuning. When selecting a channel
It is possible to shorten the tuning time.

[Brief description of drawings]

FIG. 1 is a block diagram of a tuning voltage generating circuit of a television of the present invention. FIG. 2 is a specific circuit diagram of the tuning voltage switching circuit portion of FIG. FIG. 3 is a timing chart showing the operation of FIGS. 1 and 2. FIG. 4 is a circuit diagram of a conventional tuning voltage generation circuit for a television. 2 ... Electronic tuning tuner 3 ... Tuning detection circuit 4 ... Clock generation circuit 5 ... Automatic tuning control circuit 6 ... Channel up button 7 ... Channel down button 8 ... Up-down counter 9 ... D / A Converter 10 …… Numerical judgment circuit 11 …… Tuning voltage selector circuit 12 …… VHF / UHF selector switch

Claims (1)

(57) [Claims] 1. A clock generation circuit that generates a clock signal, a counter that performs a counting operation based on the clock signal, a D / A converter that converts a count value output from the counter into a tuning voltage, and the tuning An electronic tuning tuner that performs tuning based on a voltage, a tuning button for selecting a desired channel, a tuning detection circuit that detects that the electronic tuning tuner has tuned, and outputs a tuning detection signal, When the tuning button is pressed and when the tuning detection signal is not output from the tuning detection circuit, the clock signal is supplied to the counter, and the tuning detection signal is output from the tuning detection circuit, And a control circuit for stopping the supply of the clock signal to the counter when the tuning button is not pressed. Tuning circuit to be.