JPH0323721Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an oscillation signal amplification circuit in a tuner local oscillation device.

2. Description of the Related Art A conventional structure of a local oscillation stage of a television tuner will be described below with reference to FIG. As shown in the figure, the local oscillation stage includes a local oscillation circuit 1 of a UHF tuner and a local oscillation circuit 2 of a VHF tuner,
It consists of a transistor amplifier circuit 3 having an output terminal P. The local oscillation circuit 1 of the UHF tuner is based on a Colpitts circuit, and operates by feeding power from the UHF tuner B power supply terminal UB to the collector C ₁ of the transistor Tr ₁ . When a bias tuning voltage is applied, the tuning frequency is determined by a series resonant circuit (tuning circuit) consisting of a variable capacitor C ₁ and a resonant line L ₁ .
It oscillates according to this tuning frequency. The oscillation signal is then extracted by the resonant line L ₂ and applied to the amplifier circuit 3. The local oscillation circuit 2 of the VHF tuner is also based on the Colpitts circuit, and it switches between high band and low band, and each B power supply terminal
It operates by feeding power from HB and LB to the collector C ₂ of transistor Tr ₂ , and connects the tuning terminal to variable capacitor C ₃ .
It oscillates according to the tuning frequency determined by applying a reverse bias voltage from Tu. The oscillation signal is then extracted from the variable capacitor C ₃ and applied to the amplifier circuit 3.

The local oscillation signals of VHF and UHF are transmitted to a VHF mixing circuit (not shown) or a UHF mixing circuit (not shown) before or through the amplifier circuit 3.
(not shown).

Amplifier circuit 3 is a grounded emitter type, and is compatible with UHF and VHF.
Since it needs to operate at the same time as receiving, it works as an IF amplifier when receiving UHF, and when receiving VHF.
Always powered to work as a VHF mixer
It operates by being supplied with power from the B power supply terminal MB for the VHF mixing circuit (not shown), and amplifies the oscillation signals taken out from the UHF or VHF tuner section and each local oscillation circuit 1 and 2. ), output to a VHF mixing circuit (not shown), or output to an external output terminal P.

To describe the arrangement of each part of the tuner, the circuit is configured on a printed circuit board, installed in a frame-shaped shield base, and installed in a shield case with shield covers installed at the upper and lower openings, respectively.

For example, an antenna input terminal (not shown) is placed on one of the short sides of the frame-shaped shield base, and each power supply terminal (UB, HB, LB, TU, and MB) is placed on one of the long sides.
and an IF output terminal (not shown).

Here, since the external output terminal P of the local oscillation signal is a high-frequency signal, the structure of the terminal and the need to place it in a location separate from the antenna input terminal (not shown) are important.
Placed on the other short side.

On the other hand, to explain the layout of each circuit on the printed circuit board, first, the VHF mixing circuit is the last stage, so it is on the opposite side of the antenna input terminal, and it is close to the IF output terminal, that is, on the other side of the short side of the shield base. Placed on one side. Therefore, the VHF mixed circuit B power supply terminal MB is located on the long side and near the other short side.

UHF local oscillation circuit 1 and VHF local oscillation circuit 2
Since it is preferable that the antenna terminals be located far from the antenna input terminal (not shown), they are arranged in an empty space on the other side of the short side, that is, on the other side of the long side and in the middle.

By the way, the amplifier 3 includes the UHF local oscillation circuit 1,
It is preferable that the UHF local oscillation circuit 2 and the external output terminal P be close to each other, so the other short side of the shield base and both the UHF and VHF local oscillation circuits 1,
It is preferable to arrange it between the center and the other long side from the center.

Problems to be Solved by the Invention According to the above-described conventional local oscillation circuit, the operating power of the oscillation signal amplifier circuit 3 is supplied from the operating power of the VHF mixing circuit. Therefore,
The power supply line of the amplifier circuit 3 becomes longer, which makes it easier to pick up noise signals, and the tuner becomes larger due to the wiring.

Means for Solving the Problems The present invention provides a local oscillation device for the tuner section, which is composed of local oscillation circuits in the UHF and VHF tuner sections, and a transistor amplification circuit that amplifies the local oscillation signal and outputs it to an external output terminal. , the operating power supply of the oscillation signal amplification circuit is connected to the power supply line of the UHF tuner section and the power supply line of the VHF tuner section through diodes, respectively.

Function In the local oscillator stage, if the power supply for the oscillation signal amplification circuit is connected to the UHF tuner power line and the VHF tuner power line with diodes, there is no need to wire the amplification power supply from the mixed circuit side, Power line available.

Embodiment An embodiment of the present invention will be described below with reference to FIG. The same reference numerals as in FIG. 2 indicate the same parts. In the figure, 1 is the local oscillation circuit of the UHF tuner section,
2 is a local oscillation circuit of the VHF tuner section, and 3 is a transistor amplifier circuit that amplifies the generated oscillation signal and outputs it to the mixing circuit. The feature of this invention is that the power supply of the amplifier circuit 3 is connected to the B power terminals UB, HB, LB of each local oscillation circuit 1, 2 of the UHF and VHF tuner section.
B power terminal for UHF tuner by supplying from
UB to transistor Tr ₃ by diode D ₁ ,
And power supply line for VHF tuner B power terminal HB, LB (collector C ₂ of transistor Tr ₂ )
are connected to transistor Tr ₂ by diode D ₂ .

That is, according to the above configuration, when voltage is applied to the B power supply terminal UB during UHF reception, the diode
_D1 is forward biased, diode _D2 is reverse biased, and power is supplied from the B power supply terminal UB to the amplifier circuit 3. Then, the local oscillation circuit 1 oscillates according to the tuning frequency determined by applying a reverse bias tuning voltage from the tuning terminal Tu to the tuning circuit consisting of the resonant line L ₁ and the variable capacitor C ₁ , and this oscillation signal is transmitted to the amplifier circuit 3. The signal is amplified and sent out from the external output terminal P. Next, when a voltage is applied to the B power supply terminal HB or LB of the high band or low band during VHF reception, diode D ₂ becomes forward biased and diode D ₁ becomes reverse biased, and the amplifier circuit 3 is supplied from the B power supply terminal HB or LB. Powered by Then, it oscillates according to the tuning frequency determined by applying a reverse bias voltage to the variable capacitor _C3 from the tuning terminal Tu.
This oscillation signal is amplified by the amplifier circuit 3 and sent out from the external output terminal P.

Effects of the invention According to the invention, in the tuner's local oscillation device, the power supply for the oscillation signal amplification circuit is connected to the power line of the UHF tuner section and the power line of the VHF tuner section by a diode, so that the VHF mixing circuit There is no need to supply power, and the power line for the amplifier circuit 3 does not need to be routed, making it shorter, so the tuner can be made smaller and the jamming performance is improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a local oscillation circuit for a tuner according to the present invention, and FIG. 2 is a circuit diagram of a conventional local oscillation circuit for a tuner. 1...Local oscillation circuit of UHF tuner section, 2...
...VHF tuner section local oscillation circuit, 3...Transistor amplifier circuit, UB...UHF tuner section power line, HB, LB...VHF tuner section power line, _D1 , _D2 ...Diode, P... External output terminal.

Claims (1)

[Scope of utility model registration request] It is equipped with each local oscillation circuit of the UHF and VHF tuner sections, a common amplification circuit for amplifying the generated oscillation signal, and a terminal for externally outputting the amplified oscillation signal, and the power supply for the amplification circuit is
A local oscillation device for a tuner, characterized in that it is connected to a power line of a UHF tuner section and a power line of a VHF tuner section through diodes, respectively.