JPH09181987A - Input circuit for electronic tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the input circuit of an electronic tuner, which sufficiently secures the attenuation quantity of a VHF signal at the time of UHF reception, by providing a trap circuit between the contact point of an input terminal and a VHF tuning circuit and a UHF tuning circuit. SOLUTION: The input terminal 1, the trap circuit 2 to which the signal of the input terminal 1 is supplied, the UHF tuning circuit 3 connected to the output of the trap circuit 2, a UHF output terminal 4 connected to the output of the UHF tuning circuit 3, the VHF tuning circuit 5 to which the signal of the input terminal 1 is supplied, and a VHF output terminal 6 are provided. The trap circuit 2 operates as a VHF trap at the time of UHF reception and it is the input circuit of the electronic tuner operating as a VHF image trap. When the trap circuit 2 sets a trap frequency to the VHF signal, the attenuation quantity of the VHF signal at the time of UHF reception can sufficiently be secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input circuit of an electronic tuner used in a television receiver.

[0002]

2. Description of the Related Art An input circuit of a conventional electronic tuner will be described below.

As shown in FIG. 3, an input circuit of a conventional electronic tuner has an input terminal 21, a high-pass filter 22 to which a signal from the input terminal 21 is supplied, and a UHF connected to an output of the high-pass filter 22. A tuning circuit 23, a UHF output terminal 24 connected to the output of the UHF tuning circuit 23, and a VHF to which a signal from the input terminal 21 is supplied.
It is composed of a tuning circuit 25 and a VHF output terminal 26 connected to the output of the VHF tuning circuit 25. The high pass filter 22 has a capacitor 2 between its input and output.
7 is connected, and an inductance 28 is connected between the output side of the capacitor 27 and the ground, which is a so-called first-order K-type filter.

The input terminal 21 has a VHF signal (a desired signal of about 90 to 222 MHz in the case of the Japanese channel) and a UHF signal.
Signal (desired signal about 470-77 for Japan channel)
0 MHz) is input.

When receiving VHF, the input signal is input to the VHF tuning circuit 25 while the VHF image signal is attenuated by the high-pass filter 22. The VHF tuning circuit 25 tunes to a single channel of the VHF signal, and the desired channel of the VHF signal is output from the output terminal 26.

On the other hand, when receiving UHF, the high-pass filter 22
Sets its cutoff frequency to about 400 MHz to attenuate the VHF signal and allow the UHF signal to pass. This UHF signal is tuned by the UHF tuning circuit 23, and a single desired signal is output from the output terminal 24.

[0007]

However, in such a conventional configuration, since the high-pass filter is a first-order K-type filter and its selectivity is gradual, a sufficient amount of attenuation of the VHF signal during UHF reception is secured. There was a problem that I could not do it.

The present invention solves this problem.
It is an object of the present invention to provide an input circuit of an electronic tuner that sufficiently secures the amount of attenuation of VHF signals when receiving UHF.

[0009]

In order to achieve this object, an input circuit of an electronic tuner of the present invention is connected to an input terminal, a trap circuit to which a signal of this input terminal is supplied, and an output of this trap circuit. And a UHF output terminal connected to the output of this UHF tuning circuit,
The trap circuit includes a VHF tuning circuit to which a signal from the input terminal is supplied and a VHF output terminal connected to the output of the VHF tuning circuit. The trap circuit functions as a VHF trap when receiving UHF and a VHF image trap when receiving VHF. It is configured to work as. With this configuration, it is possible to sufficiently secure the amount of attenuation of the VHF signal when receiving UHF.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is an input terminal, a trap circuit to which a signal from the input terminal is supplied, and a UH connected to the output of the trap circuit.
An F tuning circuit, a UHF output terminal connected to the output of the UHF tuning circuit, and V to which a signal from the input terminal is supplied.
An HF tuning circuit and a VHF output terminal connected to the output of the VHF tuning circuit are provided, and the trap circuit is UHF.
It functions as a VHF trap when receiving, and
It is an input circuit of an electronic tuner that functions as a VHF image trap at the time of reception, and if the trap frequency is set to the VHF signal by this trap circuit, only the VHF signal of the input signal can be attenuated. Therefore, the amount of attenuation of the VHF signal at the time of receiving UHF can be sufficiently secured.

The trap circuit of the invention described in claim 2 is
The electronic tuner according to claim 1, wherein a parallel connection body of the capacitor and the first inductance is connected between the input and the output, and a second inductance is connected between the output side of the parallel connection body and the ground. Input circuit of 1
With a simple configuration in which only individual inductances are added, steep attenuation characteristics can be obtained compared to a high-pass filter.

The invention according to claim 3 is the input circuit for an electronic tuner according to claim 2, wherein the input impedance of the UHF tuning circuit is constituted by an inductance, and this inductance is used as one element of the trap circuit.
It is possible to attenuate the VHF image signal during reception in the HF band and reduce VHF interference during reception in the UHF band.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an input circuit of an electronic tuner according to an embodiment of the present invention. The input circuit of the electronic tuner of the present invention includes an input terminal 1
And the trap circuit 2 to which the signal of the input terminal 1 is supplied
And a UHF tuning circuit 3 connected to the output of the trap circuit 2 and a U connected to the output of the UHF tuning circuit 3.
It is provided with an HF output terminal 4, a VHF tuning circuit 5 to which the signal from the input terminal 1 is supplied, and a VHF output terminal 6 connected to the output of the VHF tuning circuit 5.

In the present embodiment, the trap frequency of the trap circuit 2 is set to about 265 MHz. For this reason, U
Of the signals input to the trap circuit 2 when receiving HF, the VHF signal (for the Japanese channel, the desired signal is about 90
222 MHz) and passes only the UHF signal.

FIG. 2 shows a pass characteristic 15 of the input circuit of the electronic tuner in one embodiment of the present invention and a pass characteristic 16 of the input circuit of the electronic tuner in the conventional example.

As described above, according to the present invention, the input terminal 1
By providing the trap circuit 2 between the connection point of the VHF tuning circuit 5 and the UHF tuning circuit 3 and setting the trap frequency within the VHF signal, the VHF signal can be sufficiently attenuated when the UHF signal is received.

Further, in the trap circuit 2 shown in FIG. 1, a parallel connection body of the capacitor 7 and the first inductance 8 is connected between the input and the output, and the output side of the parallel connection body and the ground are connected. The second inductance 9 is connected between them.

Here, the capacitor 7 is C, the first inductance 8 is L _1, and the second inductance 9 is L ₂ .

At the time of receiving VHF, a VHF image trap is formed by the capacitor 7, the first inductance 8 and the second inductance 9, and the VHF image trap frequency is (Equation 1).

[0020]

[Equation 1]

For example, C = 12 pF, L ₁ = 45 nH, L ₂
= 40 nH, the VHF image trap frequency is about 316 MHz and most VHF image signals can be attenuated.

Upon reception of UHF, a VHF trap is formed by the capacitor 7 and the first inductance 8, and this VHF trap is formed.
The trap frequency is (Equation 2).

[0023]

[Equation 2]

For example, if C = 12 pF and L ₁ = 45 nH, the VHF trap frequency becomes about 217 MHz and VHF becomes VHF.
The signal can be attenuated.

The input impedance of the UHF tuning circuit 3 is equivalent to the inductance 10 when receiving VHF. Here, focusing on the fact that the inductance 10 is connected in parallel with the second inductance 9,
Since the value of L _{2 in} (Equation 1) changes, the VHF image trap frequency also changes. In this embodiment, the inductance 10 is about 200 nH, which is about 332 MHz, which is the optimum value.

By using the input impedance of the UHF tuning circuit 3 as described above, the trap circuit is UH
The trap frequency is switched to the optimum value when F is received and when VHF is received.

[0027]

As described above, according to the present invention, a trap circuit is provided between the connection point between the input terminal and the VHF tuning circuit and the UHF tuning circuit, and the trap frequency is set in the VHF signal, whereby the UHF signal is generated. The VHF signal can be sufficiently attenuated during reception.

[Brief description of the drawings]

FIG. 1 is a block diagram of an input circuit of an electronic tuner according to an embodiment of the present invention.

FIG. 2 is a diagram showing a pass characteristic of the input circuit of the electronic tuner according to the embodiment of the present invention and a pass characteristic of the input circuit of the electronic tuner according to the conventional example.

FIG. 3 is a block diagram of an input circuit of a conventional electronic tuner.

[Explanation of symbols]

 1 Input Terminal 2 Trap Circuit 3 UHF Tuning Circuit 4 UHF Output Terminal 5 VHF Tuning Circuit 6 VHF Output Terminal

Claims (3)

[Claims] 1. An input terminal, a trap circuit to which a signal from the input terminal is supplied, a UHF tuning circuit connected to the output of the trap circuit, and a UHF output terminal connected to the output of the UHF tuning circuit. , A VHF tuning circuit to which a signal from the input terminal is supplied, and a VHF output terminal connected to the output of the VHF tuning circuit. The trap circuit functions as a VHF trap during UHF reception and a VHF image during VHF reception. The input circuit of an electronic tuner that acts as a trap. 2. The trap circuit has a capacitor and a first inductance connected in parallel between its input and output, and a second inductance connected between the output side of this parallel connection and ground. The input circuit of the electronic tuner according to claim 1. 3. The input circuit of an electronic tuner according to claim 2, wherein the input impedance of the UHF tuning circuit is constituted by an inductance, and the inductance is used as one element of the trap circuit.