JPS5840871B2 - tv jiyeonji yuzouki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides video intermediate frequency (VIP)
) circuit (Special feature) A trap circuit is provided to attenuate the audio carrier signal of the video intermediate frequency signal obtained from the tuner output. If the input electric field is relatively weak, the attenuation will be increased according to the strength of the input electric field, and if the input electric field is relatively weak, the attenuation will be reduced according to the strength of the input electric field. The present invention relates to a television receiver that has a constant attenuation amount with respect to an input electric field.

Generally, the VIP circuit requires a band corresponding to about 4 MHz EC, which is the band of the video signal.

However, as shown in FIG. 1, the video carrier A (52,75 MHz) of the upper adjacent channel, the audio carrier B (60,25 MHz) of the lower adjacent channel, and the audio carrier C ( 54,2
5MHz) enters the sandwich circuit, it interferes with the video signal and impairs the image quality.

Therefore, in order to remove these interfering signals, television signals are currently transmitted using the vestigial sideband method.
Place the video carrier wave at a position of 16 dB from the peak of the characteristic,
Using a trap circuit together, the video carrier A of the upper adjacent channel of 52.75 MHz is set to 150 dB or more, and 60.
The audio carrier wave B of the 25-MHz lower adjacent channel is set to be greater than 16 OdB.

In addition, the 54.25 MHz own station audio carrier C is affected by the beat of the 4.5 MHz audio intermediate frequency signal (SIF signal) and the 3.58 MHz color subcarrier signal (920 kHz interference caused by the 4.5 MHz audio intermediate frequency signal (SIF signal) in the video detection circuit Considering interference to the .5MHz sandwich circuit, it is attenuated by approximately -26dB.

Therefore, the audio intermediate frequency signal of 4.5 Mf(z) is sufficiently amplified through the limiter circuit before audio detection.

With this current method, there is no problem when receiving at a normal electric field strength, but when the input electric field becomes very weak, the 54.25 MHz trap circuit always has a certain degree of attenuation. Therefore, the 4.5 MHz component becomes extremely small, causing problems such as a drop in the S/H of the audio signal and furthermore, no audio being produced.

On the other hand, when the electric field input becomes extremely strong, -26d
Attenuation of B alone is insufficient, and 920KHz appears on the screen.
This results in the inconvenience of beat interference or 4.5 MHz interference.

FIG. 2 is an electrical block diagram showing the conventional technology, in which 1 is an antenna, 2 is a tuner, and 3 is a 52.75MHz
upper adjacent channel video carrier trap circuit, 4 is 5
4.25MHz audio carrier trap circuit, 5 is 60.
25MHz lower adjacent channel audio carrier trap circuit, 6 is VIP amplifier circuit, 7 is video detection circuit, 8 is video signal processing circuit, 9 is audio intermediate frequency detection circuit, 10 is audio intermediate frequency signal processing circuit, 11 is automatic Gain control (AG
C) circuits, but since their basic functions are already known, further detailed explanation will be omitted.

Now, the present invention attempts to change the amount of attenuation of the 54.25 MHz audio carrier trap circuit 4 by changing the input quantum field strength, and the automatic gain control (AGC) circuit 11
Focusing on the fact that the output voltage of the AGC circuit 11 depends on the input electric field strength, the output voltage of the AGC circuit 11 is used to change the trap amount.

FIG. 3 shows the audio carrier trap circuit 4 in FIG.
This trap circuit is a commonly used circuit, and in the figure, r is the equivalent resistance of the inductance L.

This trap circuit is used when the amount of attenuation must be sufficiently deep.
The equivalent circuit of the C1゜r, L, 02 part is shown. If the resistors in Figure 3 are selected so that Zc in Figure 4 becomes can be made larger.

Further, the amount of attenuation can also be adjusted depending on the value of the resistor R.

Note that the equivalent inductance L in FIG.

is the value when the resonant frequency due to the inductance L and capacitor C2 in Fig. 3 is selected slightly higher than 54.25 MHz, and the inductive reactance is very high at 54.25 MHz. These are three methods commonly used to increase the impedance at points other than the resonance point, that is, to increase the Q.

Now, referring again to FIG. 3, the emitter and collector of the transistor 13 are connected to both ends of the resistor R, and the base is connected to the output terminal of the automatic gain control circuit 11.

Therefore, when the output of the automatic gain control circuit 11 changes according to the input electric field strength, the transistor 1 changes according to the change.
The impedance between the emitter and collector of 3 changes,
Equivalently, the value of the resistor R is changed to adjust the amount of attenuation.

In the circuit shown in FIG. 3 described above, the control voltage applied to the transistor 13 varies linearly from a weak electric field to a strong electric field as shown in FIG. 1) As can be seen from the equation, the transistor 1
Equivalently change the value of resistance R by changing the impedance of 3 (if you change this, you will change not only the attenuation amount but also the resonance point at the same time, which will cause the trap to shift position,
On the contrary, there is a possibility that it will encourage beat interference.

The present invention eliminates the drawbacks of the above-mentioned prior art 1, and when the input electric field is weak, the S/N ratio of the audio is not impaired.
In addition, if the input electric field is strong, 920kHz interference and
．． This is an attempt to eliminate beat interference on a 5MHz screen.

FIG. 5 shows a circuit according to an embodiment of the present invention, which was designed to avoid the above-mentioned disadvantages in the circuit 1 shown in FIG.
The attenuation amount is changed only in the case of a weaker electric field or a stronger electric field.

In FIG. 5, it is assumed that the output voltage of the automatic gain control circuit 11 changes as shown in FIG. 6a.

This output voltage is connected to a resistor 14, a diode 15, and a DC power supply 1.
A slicing circuit consisting of 6 slices below E level,
Next, transistor 17, diode 18, resistor 19
When the level is shifted by a circuit consisting of the following, a control voltage as shown in FIG. 6 is obtained at the connection point between the diode 18 and the resistor 19.

On the other hand, if a slice circuit consisting of a resistor 21, a diode 22, and a DC power supply 23 slices the E2 level or higher, a control voltage as shown in FIG. 6C is obtained.

If these two control voltages are combined by resistors 20 and 26, the control voltage shown in FIG.
Can be supplied on a base of 3.

“As is clear from the above description, according to the present invention, 7
920kHz becomes noticeable when there is a relatively strong electric field of 0dB or more
It is possible to reduce screen interference at z beat and 4.5 MHz, and it is possible to improve the audio S/N, which is a problem in relatively weak electric fields of 40 dB or less.
This allows stable operation without causing problems such as trap displacement.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the own station reception signal and the adjacent channel signal, Figures 2 and 3 are electrical circuit diagrams for explaining the conventional technology, and Figure 4 is the electrical equivalent of Figure 3. A circuit diagram, FIG. 5 is a specific electric circuit diagram showing one practical example of the present invention, and FIG.
7 to 7 are input electric field-control voltage characteristic diagrams for explaining the present invention. 1...Antenna, 2...Tuner, 3
. . . Upper adjacent channel video carrier trap circuit, 4 . . . Own station audio carrier trap circuit, 5.
. . . Lower adjacent channel audio carrier trap circuit, 6 . . VIF amplifier circuit, 7 . . . Video detection circuit, 8 . . . Video signal processing circuit, 9.
...Audio intermediate frequency detection circuit, 10...Audio intermediate frequency signal processing circuit, 11...Automatic gain control circuit.

Claims (1)

[Claims] 1. In a trap circuit that attenuates the audio carrier signal of the video intermediate frequency signal obtained from the tuner output of the television receiver, a variable impedance element is provided to control the amount of attenuation of the trap circuit, and an automatic gain control circuit is installed. Based on the output voltage from 1, in an input electric field above a certain level, it changes in one direction, and in an input electric field under running wind, it changes in the other direction, and the normal input between these two force directions. 1. A television receiver comprising a circuit for creating a control voltage that does not change in an electric field, and controlling the variable impedance element using the control voltage created by the circuit.