JPS6138288Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an input switching device for a tuner.

Although most of the VHF tuners in recent television receivers are becoming electronic tuners, there is still a strong demand for mechanical tuners in some low-cost television receivers, reducing the cost of VHF tuners. is requested.

Mechanical tuners are generally classified into various types depending on the inductor switching mechanism, such as switch type, turret type, and discret type. In the case of a switch-type tuner, the UHF/VHF switching mechanism can be relatively easily reduced in cost by increasing the position of the rotary switch and the number of circuits, but in the case of a discret-type tuner, the contact mechanism is changed to a switch-type tuner. Although it is cheaper compared to
There were disadvantages in terms of cost, such as having to use a micro switch or a dedicated contact plate as the UHF/VHF switching mechanism.

In other words, as a function of this UHF/VHF switching mechanism,
When receiving a UHF channel, it is necessary to supply +B power to the UHF tuner, accept the signal converted from the UHF signal to the IF frequency, and reject the VHF signal. Therefore, in conventional discret type tuners, local oscillation switching mechanism,
In addition to the three contact plates for the high frequency amplification interstage circuit switching mechanism and the high frequency amplification input circuit switching mechanism, UHF/VHF
Since one more contact plate is used as a switching mechanism, the tuner body becomes larger and the cost increases.

The present invention was developed in view of these points, and is a discreet type tuner.
The present invention provides an input switching device that aims to reduce the number of contact plates and reduce costs by digitizing the UHF/VHF switching mechanism.

Hereinafter, the present invention will be explained according to embodiments shown in the drawings.

The drawing shows a circuit configuration diagram of an input switching circuit of a high frequency amplifier of a VHF tuner, in which 1 represents an input tuning switching circuit formed on a contact plate for switching the high frequency amplifier input circuit, and the circuit 1 includes circuits 1 to 1. 12
Each contact for the VHF channel and the contact for the UHF channel are provided, and inductors L ₁ , L ₂ , L ₃ ...L ₁₃ and capacitors C ₁ , C ₂ are connected to each contact for channels 1 to 12 as before. A resistor R ₁ is also connected between the contacts of the UHF channel.
2 is a high frequency amplification circuit consisting of a transistor Q ₁ , resistors R ₂ and R ₃ , and capacitors C ₃ and C ₄ , etc.;
In addition, 3 is a UHF signal added especially for this invention.
This is a VHF switching circuit. The switching circuit 3 is composed of a transistor Q ₂ , a diode D ₁ , resistors R ₄ , R ₅ , and capacitors C ₅ , C ₆ , C ₇ . 4 is VHF antenna connection terminal, 5 is UHF IF signal input terminal, 6
1 is a power supply +B supply terminal, 7 is a power supply terminal for the UHF tuner, and 9, 10, and 11 are contact brushes that are brought into contact with the respective contacts of the input tuning switching circuit 1.

Currently, when receiving a VHF channel, brush 9,
10 and 11 are in contact with the contacts of the VHF channel, and a predetermined inductor is connected in parallel with the capacitor _C10 . At this time, connect terminal 4 from the VHF antenna.
The high frequency signal obtained is connected to the capacitors C9, _C10 ,
Amplification transistor via C ₁₁ , coil L ₁₄ , etc.
The high frequency signal of a _{predetermined} VHF channel is selectively amplified in the high frequency amplifier circuit 2. When receiving this VHF channel, the brush 10 is in an open state in terms of direct current, so
The diode D1 of the UHF/VHF switching circuit ₃ is in a cut-off state, and since no bias is applied to the transistor _Q2 , the transistor _Q2 is in a cut-off state. Therefore, in this case, power +B is not supplied to the UHF tuner, and the UHF tuner is in a non-operating state.

On the other hand, when receiving a UHF channel, brushes 9, 1
A resistor R ₁ is inserted between 0 and 9 is directly grounded, and the brush 10 is grounded via the resistor R ₁ . Therefore, at this time, from the power supply +B to the resistor
A DC current flows to the ground via R ₄ , the diode D ₁ , and the resistor R ₁ , and a DC current flows from the power supply +B to the ground via the transistor Q ₂ , resistors R ₅ and R ₁ , and the diode D ₁ and the transistor Q ₂ Both are in the on state. As a result, the power supply +B is supplied from the power supply terminal 7 to the UHF tuner via the transistor _Q2 , and the UHF tuner becomes operational, and at this time, the UHF tuner obtained from the UHF tuner
The IF signal is supplied from the input terminal 5 to the base of the high frequency amplification transistor Q ₁ via the capacitor C ₁₂ , the diode D ₁ , the coil L ₁₄ and the capacitor 11, and the IF signal is amplified.

In this way, in this embodiment, the diode D ₁ and the transistor Q ₂ of the UHF/VHF switching circuit 3 are controlled on/off depending on whether a UHF channel is received or a VHF channel is received, and power is supplied to the UHF tuner especially when a UHF channel is received. At the same time, the IF signal is supplied from the UHF tuner to the high frequency amplification circuit 2 of the VHF tuner.

According to the input switching device of the present invention, in a mechanical VHF tuner such as a discrete tuner, the UHF/VHF switching circuit is turned on/off between the UHF receiving contacts of the input tuning switching circuit for switching the high frequency amplification input circuit. A resistor is installed to control the operation.
The UHF IF that supplies power to the UHF tuner and is obtained from the UHF tuner when receiving a UHF channel.
Since the signal is supplied to the high frequency amplification circuit, there is no need to use a dedicated contact plate for switching between the UHF power supply and UHF IF signal as in the past, which is extremely advantageous in reducing the size and cost of the VHF tuner. Become.

[Brief explanation of drawings]

The drawing is a circuit configuration diagram of an embodiment of the device of the present invention. 1...Input tuning switching circuit, 2...High frequency amplification circuit, 3...UHF/VHF switching circuit, 4...VHF antenna connection terminal, 5...UHF IF signal input terminal,
6...Power +B supply terminal, 7...UHF tuner power supply terminal.

Claims (1)

[Claims for Utility Model Registration] In a mechanical VHF tuner, an input tuning switching circuit comprising a plurality of contacts for a VHF channel and a contact for a UHF channel, and a resistor inserted between the contacts for the UHF channel; When a predetermined channel contact for the VHF channel in the input tuning switching circuit is selected,
A high frequency amplification circuit that selectively amplifies the high frequency signal from the VHF antenna related to this selected channel, a UHF IF signal input terminal, a power supply terminal to the UHF tuner, and one of the input tuning switching circuits for the VHF channel. When that contact is selected, it turns off, and when the contact for the UHF channel in the input tuning switching circuit is selected, it is grounded through the resistor and turns on.
It consists of a UHF/VHF switching circuit, and when the UHF/VHF switching circuit turns on, it supplies the power supply voltage from the power supply terminal to the UHF tuner to the UHF tuner to put it into operation, and also outputs the UHF IF signal. from the input terminal
An input switching device for a tuner, characterized in that it guides a UHF IF signal to the high frequency amplification circuit and amplifies it.