JPH0127294Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a circuit for presetting a tuning voltage in a tuning device for an electronic tuner using a variable capacitance diode as a tuning element.

2. Description of the Related Art As a channel selection means for a television receiver that selects a channel by applying a tuning voltage to a variable capacitance diode, there is a circuit arrangement having a circuit arrangement as shown in FIG. 1 in principle. Reference numeral 1 designates an electronic tuner using a variable capacitance diode _D1 as a tuning element, and a tuning voltage _Et is applied to one end of the tuner via a resistor so as to tune to the frequency of a predetermined channel.
As is well known, in the case of television receivers, the tuning voltage E _t is set in advance for each channel, so that when selecting a channel, the specified channel can be immediately selected using a channel selection switch. . Recently, this tuning voltage
As a presetting means for E _t , there is a method in which a semiconductor memory 2 is used and each tuning voltage E _t is sequentially stored in this memory. i.e. power supply
Potentiometer VR ₁ and resistor R ₂ between E ₁ and ground
A voltage divider consisting of a voltage divider is provided, and the tuning voltage E _t taken out by this one potentiometer VR ₁ is
is applied to the electronic tuner ₁ via the preset switch SW1. When the first channel is tuned in the best condition, the tuning voltage _Et at that time is applied to the input terminal _S1 of the semiconductor memory 2 via the tuning switch _SW2 . Next, in order to preset the second channel, move the contact piece of switch SW ₂ to contact point S ₂ , and switch the potentiometer VR _1.
synchronize with it. Thereafter, the tuning voltage _Et of each channel is preset in the same manner. In this case, band switching must be performed according to the frequency band of the channel. This is because the linear region of the variable capacitance diode _D1 is limited, and a capacitance value over the entire frequency band cannot be obtained. Therefore, the fixed inductance of the coil of the tuned circuit is changed by band switching, and the same area is used for capacitance changes. Therefore, in the case of a television receiver,
The band is divided into three bands: VHF band low band, VHF band high band, and UHF band, and for each band, switch the band change switch SW ₃ to VL, VH, and U to select the several channels that exist in each band. In contrast, the tuning voltage is preset. This interpolation means that the potentiometer VR ₁ is scanned three times from the lower potential a to the higher potential b. Since a single potentiometer is used here, the knob must be reversed each time at the beginning of the band, which is extremely troublesome as a presetting operation at the time of shipment from the factory.

This proposal was proposed focusing on the above-mentioned problem, and provides a circuit arrangement for speeding up the presetting operation in a tuning device that uses a memory device and presets the tuning voltage with a single potentiometer. It is. FIG. 2 shows the main circuit layout of the embodiment of the present invention.

In Fig. 2, switches SW ₄₁ and SW ₄₂ that operate in conjunction with band changeover switch SW ₃ are potentiometers.
Located at each end of VR ₁ . Contacts VL and U of switch SW ₄₁ and contact VH of switch SW ₄₂ are connected to power supply E ₁ (33V), and contacts VH of switch SW ₄₁ and contacts VL and U of switch SW ₄₂ are grounded.

By providing the switches SW ₄₁ and SW ₄₂ as shown in FIG. 2, the scanning of the knob of the potentiometer VR ₁ is as follows. When the switches SW ₄₁ and SW ₄₂ are set at the contact point VL, the knob is sequentially moved from a to b while setting the tuning voltage E _t . When you reach side b, switch
SW ₄₁ and SW ₄₂ are now connected to contact VH. The relationship between the voltage supply terminals of the resistor of potentiometer VR ₁ is then reversed. Therefore, the knob is moved from the opposite direction b toward a while performing preset tuning. Then, the switches SW ₄₁ and SW ₄₂ are connected to the contact point U, the switch is reversed, and the knob is moved from a to b again. In other words, unnecessary movements in the operation of potentiometer VR ₁ can be removed.

As explained above, in the present invention, the polarity of the DC voltage supplied to the potentiometer can be reversed for each unit of a predetermined frequency band, and the potentiometer can be connected. Therefore, this makes it possible to speed up the tuning voltage presetting work.

[Brief explanation of the drawing]

FIG. 1 is a principle circuit diagram of a conventional channel selection device which is the background of the present invention, and FIG. 2 is a circuit diagram of a main part of a channel selection device according to an embodiment of the present invention. D ₁ ... variable capacitance element, VR ₁ ... potentiometer, 2 ... memory device, 1 ... electronic tuner,
SW ₄₁ and SW ₄₂ ...Reverse switch, SW ₃ ...Band switching means.

Claims (1)

[Claims for Utility Model Registration] A variable capacitance diode is used as a tuning element, and the tuning voltage applied to the variable capacitance diode is controlled by one potentiometer whose both ends are connected to a DC power supply, and for each unit of a predetermined frequency band. The tuning voltage value for each channel, which is set in advance by the potentiometer, is sequentially written into a memory device, and when selecting a channel, the tuning voltage for a predetermined channel is set from the memory device. A tuning device for an electronic tuner configured to read data and apply it to the variable capacitance diode, wherein the connection relationship between both ends of the potentiometer and both ends of the DC power source is alternately changed according to switching of the band switching means. A channel selection device equipped with an inversion switch that is inverted.