JPH1065498A - Trap circuit device for television receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive a video image with high image quality and high quality by selecting a trap frequency depending on a VHF band and a UHF band so as to attenuate a disturbing wave with a high attenuation. SOLUTION: A 1st trap circuit A in the trap circuit 3 is a fixed characteristic trap circuit and a 2nd trap circuit B is a trap circuit whose trap characteristic is made variable. A bias voltage of 0V is applied to a tuner 2 and a voltage application terminal 6. Thus, a varactor diode D1 as a changeover means has a prescribed capacitance. A trap frequency of the trap circuit B consisting of a coil L1 of a transformer T1 and capacitors C3, C4 is a trap frequency of a VHF band. S bias voltage of 5V is applied to the tuner 2 and the voltage application terminal 6. Thus, the varactor diode D1 receives a prescribed different capacitance. Then the trap frequency is a trap frequency for a UHF band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trap circuit device used in a television receiver capable of receiving a PAL system broadcast as a television broadcasting system in Europe and the like.

[0002]

2. Description of the Related Art Conventionally, in a television receiver for receiving a broadcast of the PAL system, in the PAL system, the frequency bandwidth of each channel is 7 MHz in the VHF band and 8 MHz in the UHF band. For this reason, in the frequency-converted IF band, it is necessary to trap the video carrier fp of the adjacent upper and lower receiving channels in the VHF band and UHF band, but the VHF band having a different frequency bandwidth is required. There is no trap circuit device capable of obtaining a trap characteristic capable of obtaining a sufficient attenuation in both the UHF band and the UHF band.

A conventional trap circuit device in the PAL system will be described below with reference to the drawings. FIG. 3 is a block diagram showing a conventional PAL type intermediate frequency amplifying circuit device, and FIG. 4 is a frequency characteristic diagram showing trap frequency characteristics of a conventional trap circuit device. In FIG.
The television signal input from the antenna 1 is input to the tuner 2, amplified and frequency-converted, then output as an intermediate frequency output signal, and the intermediate frequency output signal is input to the trap circuit 3 ′. Then, after the trap circuit 3 'traps a predetermined frequency serving as an interfering wave of the immediately upper and lower adjacent channels (the channels N + 1 and N-1), a predetermined trapped output signal is output. The output signal is input to the intermediate frequency amplifier 4, amplified, and then input to the SAW filter 5. The intermediate frequency output signal from the tuner 2 is
Since the data is inverted and output, in FIG. 4, the next lower adjacent channel (N-1) is displayed on the right side.

Next, the above-described conventional trap circuit 3 'will be described in detail. This conventional trap circuit 3 '
Is composed of a first trap circuit A and a second trap circuit C. The first trap circuit A is configured such that a capacitor C1 and a capacitor C2 connected in parallel are connected in series with a coil L3. And the second trap circuit C
The capacitor C3 and the capacitor C4 connected in parallel are connected in series with the winding L4 of the transformer T2.
The resistor R1 is connected to the capacitor C connected in parallel.
1, C2 and capacitors C3, C4, respectively. Then, in one embodiment of the unique value of each component constituting the first and second trap circuits A and C, the inductance value of the coil L3 is
3.3 μH, the capacitance value of the capacitors C1 and C2 is 3.
6 pF, the capacitance value of the capacitors C3 and C4 is 2 pF,
The resistance value of the resistor R1 is 120Ω, and the inductance value of the transformer T2 is 2.2 μH. Due to these inductance values and capacitance values, as shown in the frequency characteristics of FIG. 4, unnecessary signals of the next lower channel (N-1 channel) are transferred to the image carrier (Picture) f.
p: 38.9Mz vs. 40.4Mz in the VHF band,
It has a frequency characteristic of attenuating 20 dB and attenuating 12 dB at 41.4 Mz in the UHF band which is 1 MHz apart from the VHF band.

[0005] In addition, the next higher channel (N +
For one-channel (unnecessary) signal, the video carrier f
With respect to p, the attenuation is about 30 dB in both the VHF band and the UHF band.

[0006]

However, in the conventional PAL type trap circuit, a trap circuit having a fixed trap frequency characteristic despite the fact that the bandwidth between the VHF band and the UHF band is 1 MHz apart. Therefore, in both the VHF band and the UHF band, the interference wave of the adjacent channel (mainly one below the UHF band: N-1)
In the adjacent frequency) could not be attenuated. In addition, although the television receiver can receive an image even with the attenuation due to these frequency characteristics, in order to receive a high-quality and high-quality image on a larger screen, the image carrier fp must be transmitted. All the interfering waves,
There is a demand for a trap circuit capable of receiving a high-quality and high-quality image by attenuating the image with a larger amount of attenuation.

[0007]

A trap circuit provided on the output side of a tuner of a television receiver is provided with switching means for switching a trap frequency between a VHF band and a UHF band. That is, the switching means is switched by using the applied bias voltage.

[0008] A varactor diode and a transformer are arranged in the switching means.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an intermediate frequency amplifier circuit device according to an embodiment of the present invention;
FIG. 2 is a frequency characteristic diagram showing a trap frequency characteristic of the trap circuit device according to the embodiment of the present invention. The same components as those in the conventional example are denoted by the same reference numerals.
In FIG. 1, a television signal input from an antenna 1 is input to a tuner 2, amplified and frequency-converted, and then output as an intermediate frequency output signal. The intermediate frequency output signal is input to a trap circuit 3. Is done. The trap circuit 3 traps a predetermined frequency serving as an interference wave of an adjacent channel, and then outputs a predetermined trapped output signal.
, And after being amplified, is input to the SAW filter 5. The intermediate frequency output signal from the tuner 2 is inverted and output.

Next, the trap circuit device according to the embodiment of the present invention will be described in detail. The trap circuit 3 according to the embodiment of the present invention comprises a first trap circuit A
And a second trap circuit B. In the first trap circuit A, a capacitor C1 and a capacitor C2 connected in parallel are connected in series with a coil L3, and the other end of the coil L3 is grounded. In the second trap circuit B, a capacitor C3 and a capacitor C4 connected in parallel are connected in series with a winding L1 of a transformer T1. The transformer T1 is composed of a winding L1 and a winding L2 which are inductively coupled (M-coupled), and one end of each of the windings L1 and L2 is grounded. A varactor diode D1 and a capacitor C5 as switching means are connected in series to the winding L2. The varactor diode D1 and the capacitor C
One end of a resistor R2 is connected to a connection point with the resistor 5, the other end of the resistor R2 is connected to a resistor R3, and the other end of the resistor R3 is grounded. The voltage application terminal 6 connected to the connection point between the resistors R2 and R3 has the same voltage (+5) as the bias voltage applied to the tuner 2.
V or 0 V). The resistance R1
Are connected to the other ends of the capacitors C1 and C2 and the capacitors C3 and C4 connected in parallel.

[0011] In one embodiment of the present invention, in which each of the components constituting the first and second trap circuits A and B has a unique value, the inductance value of the coil L3 is 3.3.
μH, the capacitance value of the capacitors C1 and C2 is 3.6 p
F, the capacitance value of the capacitors C3 and C4 is 2 pF, the capacitance value of the capacitor C5 is 7 pF, and the varactor diode D
1 is 9.3 pF to 26 pF (applied voltage +
5V to 0V), the resistance value of the resistor R1 is 120Ω,
The resistance value of the winding L1 of the transformer T1 is 2.2 μH, the resistance value of the winding L
The inductance value of No. 2 is 1.26 μH. Due to these inductance values and capacitance values, as shown in the frequency characteristics of FIG. 2, the next lower channel (N
-1 channel) unnecessary signal to a video carrier (Pict)
ure) fp: 40. VHF band for 38.9 Mz.
At 4 Mz, attenuate 28 dB, and the VHF band and bandwidth
It has a frequency characteristic of attenuating 30 dB at 41.4 Mz in the UHF band separated by MHz. This increases the amount of attenuation by 8 dB or more as compared with the related art. Unwanted signals of the next higher channel (N + 1 channel) are attenuated by about 30 dB with respect to the video carrier fp in both the VHF band and the UHF band.

The operation of the above-configured trap circuit device for a television receiver will be described below. The first trap circuit A is a fixed trap circuit, and the second trap circuit B is a trap circuit capable of changing trap characteristics. The first trap circuit A is connected to the next higher channel (N + 1)
Channel) and is fixed, but has a sufficient attenuation of about 30 dB as described above.

Next, the operation of the second trap circuit B will be described. First, in order to receive the VHF band, a bias voltage of 0 V is applied to the tuner 2 and the voltage application terminal 6. With the applied bias voltage of 0 V, the tuner 1 takes measures to receive the VHF band. The varactor diode D1 as one configuration of the switching means obtains a capacitance value of 26 pF with a bias voltage of 0V. The varactor diode D1 has a capacitance value of 2
With the capacitance value of 6 pF, the capacitance value of the capacitor C5 of 7 pF, and the winding L2, the equivalent total capacitance value of the transformer T1 is:
It becomes 5.5 pF. 5.5 pF of this total capacitance value
And the inductance value of the winding L2 of the transformer T1 of 1.26 μH, a resonance frequency of 60.5 MHz is obtained. By the resonance frequency of 60.5 MHz, the inductance value of the winding L1 of the transformer T1 is equivalently changed. Due to the change in the inductance value of the winding L1, the trap frequency of the trap circuit device including the winding L1 of the transformer T1 and the capacitors C3 and C4 becomes 40.4 MHz (V
(HF band trap frequency) (see FIG. 2).

Next, similarly, a bias voltage of 5 V is applied to the tuner 1 and the voltage application terminal 6 in order to receive the UHF band. With the applied bias voltage of 5 V, the tuner 2 takes measures to receive the UHF band. The varactor diode D1 as one configuration of the switching means obtains a capacitance value of 9.3 pF with a bias voltage of 5V. The total capacitance value of the transformer T1 is 4 pF due to the capacitance value of 9.3 pF, the capacitance value of the capacitor C5 of 7 pF, and the winding L2. The resonance frequency of 70.9 MHz is obtained from the total capacitance value of 4 pF and the inductance value of the winding L2 of the transformer T1 of 1.26 μH. This resonance frequency 70.9MH
By z, the inductance value of the winding L1 of the transformer T1 is equivalently changed. Then, by the change of the inductance value of the winding L1,
The trap frequency of the trap circuit device composed of the winding L1 of the transformer T1 and the capacitors C3 and C4 is:
41.4 MHz (UHF band trap frequency) (see FIG. 2).

As described above, the trap frequency of the VHF band 4
0.4MHz, UHF band trap frequency 41.4M
Hz, which is a difference of only 1 Mz, is obtained by switching the bias voltage (0 V or +5 V) applied to the voltage application terminal 6. Fine adjustment of a difference of 1 Mz in frequency is performed by a varactor diode and a winding of a transformer. The frequency is finely adjusted using the property of the transformer windings L1 and L2 due to the M coupling. Then, as shown in FIG. 2, the frequency characteristics (attenuation: 28 dB in the VHF band, UH
In the F band, 30 dB) is obtained.

As described above, the varactor diode D
1 is the same bias voltage as the voltage applied when the tuner 1 is driven to receive the VHF band and the UHF band.

[0017]

The switching circuit for switching the trap frequency between the VHF band and the UHF band is provided in the trap circuit provided on the output side of the tuner of the television receiver, and the switching is applied to the tuner. By using the bias voltage to switch the switching unit, the switching unit switches the trapping frequency between the VHF band and the UHF band.
An appropriate trap frequency can be obtained in the F band. From this, each of the V and U bands is compared with the conventional,
A trap circuit device having a large attenuation can be provided. Therefore, a high-quality and high-quality television receiver with little noise from adjacent channels can be provided. Further, since the tuner and the switching means can be driven with the same bias voltage, there is also an effect that an unnecessary bias voltage need not be generated.

Since the varactor diode and the transformer are arranged in the switching means, a difference in the capacitance value due to a difference in the bias voltage of the varactor diode and a change in the resonance point on the winding L2 side of the transformer T1 are obtained.
The degree of influence of the transformer T1 on the winding L1 changes.
This change in the degree of influence equivalently changes the inductance value of the winding L1, and switches the trap frequency at which the bandwidth of the VU band is 1Mz. As described above, only by adding a varactor diode as compared with the conventional case (the transformer is conventionally arranged), the VHF band and the UHF band
It is possible to provide a trap circuit device capable of finely adjusting and changing the difference of 1 Mz of the trap frequency from the band and having a larger amount of attenuation than the conventional one.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an intermediate frequency amplifier circuit device according to an embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram showing a trap frequency characteristic of the trap circuit device according to the embodiment of the present invention.

FIG. 3 is a block diagram showing an intermediate frequency amplifier circuit device in a conventional PAL system.

FIG. 4 is a frequency characteristic diagram showing a trap frequency characteristic of a conventional trap circuit device.

[Explanation of symbols]

 2 Tuner 3, 3 'Trap circuit 4 Intermediate frequency amplifier A First trap circuit B Second trap circuit C1-C5 Capacitor D1 Varactor diode T1, T2 Transformer

Claims (3)

[Claims] 1. A trap circuit provided on the output side of a tuner of a television receiver is provided with switching means for switching a trap frequency between a VHF band and a UHF band, and applies the tuner. A trap circuit device for a television receiver, wherein said switching means is switched using a bias voltage. 2. The trap circuit device for a television receiver according to claim 1, wherein said switching means comprises a varactor diode. 3. A voltage applying terminal for applying the same voltage as the bias voltage applied to the tuner, and a varactor diode having a variable capacitance value by the bias voltage from the voltage applying terminal. The varactor diode comprises a transformer connected to one winding, and two capacitors connected in parallel, the other winding of which is connected in series. 2. A trap circuit device for a television receiver according to claim 1.