JPS6246367Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a television receiver incorporating a so-called booster.

The booster is installed in the antenna system, that is, in front of the tuner in terms of signals, to amplify the signal from the antenna in order to improve the noise in weak electric field areas and the reduction in contrast, resulting in an extremely unsightly screen. fulfill a function. By the way, 40~
The image quality in the medium electric field region of 55 dB is sufficiently improved by the booster, but in the weak electric field, especially 25 to
In areas with a weak electric field such as 40dB, noise is also amplified, making the nozzle more noticeable on the screen.

In light of this fact, the present invention is designed to operate a booster in a weak electric field area to amplify the signal from the antenna and input it to a tuner. If the noise components mixed into the video signal are above a certain level, the high frequency components of the noisy video signal are lowered to prevent the effects of noise from appearing on the screen.

The present invention will be described in detail below according to embodiments shown in the drawings.

In FIG. 1, 1 is an antenna, 2 is an antenna terminal plate attached to a television receiver that serves as a relay between the feed line from the antenna and the subsequent lead wire, 3 is a booster, and 4 is a channel selection device 5. Therefore, the tuner 6, which is selectively set to receive the desired channel, receives an intermediate frequency signal formed by superheterodyne of the radio frequency signal from the antenna 1 and the local oscillation signal oscillated in the tuner 4 itself. A video intermediate frequency circuit amplifies and detects the video signal, and 7 is a video circuit that processes the video signal and finally drives the picture tube. 8 is a booster changeover switch with one end connected to the power supply and the other end coupled to the booster 3. When this switch 8 is turned on and power supply voltage +B is applied to the booster 3, the booster 3 is in the operating state (signal from the antenna is switched on). Otherwise, the booster 3 outputs a radio frequency signal that is not amplified (that is, when the switch 8 is turned off). 9 is the intermediate frequency circuit 6
A level detector 10 connected to the output side of the booster changeover switch 8 is a switching circuit connected to the contact (A) side of the booster selector switch 8 and also connected to receive the output of the level detector 9. 1
1 forms a part of the video circuit 7, but when the switching circuit 10 is off, it does not work at all, and when the switching circuit 10 is on, it is activated and controls the video signal in the video circuit 7. A capacitor that acts as an attenuator to reduce the level of high frequency components. Parts of the level detection circuit 9, switching circuit 10 and video circuit 7 in FIG. 1 are shown in detail in FIG.

In FIG. 2, the video circuit 7 is the intermediate frequency circuit 6.
The amplifying transistor TR 4 is connected to the terminal 12 through the resistor R ₉ and the delay line ₁₃ (this delay line is for delaying the luminance signal to match the color signal and is well known).
is applied to the base of The base side of the amplification transistor TR ₄ is provided with resistors R ₁₀ and R ₁₁ that provide bias, while the collector side is connected to and coupled to the power supply line 14 via a parallel circuit of a resistor R ₁₂ and a coil L ₁ . It is connected to one end of the capacitor 11 via a capacitor _C4 . The emitter side is coupled to the base of the next stage transistor _TR5 through an emitter resistor _R13 and a resistor _R14 .

The terminal 12 is also connected to the base of a first transistor TR ₁ of PNP type through a coupling capacitor C ₁ , and a horizontal pulse P of negative polarity is connected to the base of this transistor TR ₁ through a resistor R ₂ as shown in the figure. The first transistor _TR1 becomes conductive only when this pulse P is applied, and is in an off state otherwise. In addition to the pulse P and the video signal from the terminal 12, a power supply voltage +B is applied to the base point of the first transistor _TR1 via a resistor _R1 , and the application of the pulse P is caused by this power supply voltage +B. The off state of the first transistor _TR1 is reliably set during the period in which the first transistor TR1 is not turned on. That is, the first transistor _TR1 is set to detect the presence or absence of a noise component during the horizontal synchronization signal period. A resistor _R3 is connected between the emitter of the first transistor _TR1 and ground, and the voltage across this resistor _R3 is connected to the diode _D1.
and capacitor C across ₂ . Diode D ₁ is the first
Rectify the output of transistor TR ₁ and connect capacitor C ₂
smoothes its rectified output. The next resistor R ₄ and capacitor C ₃ work to remove ripples, but it should be understood that this is to assist in smoothing since the capacitor C ₂ alone is not sufficient for smoothing. Note that the resistor R ₄ and the resistor R ₅ also function as a bleeder resistor for determining the conduction level of the second transistor TR ₂ . Second transistor TR ₂
The emitter of the transistor TR3 is grounded, and the collector thereof is directly connected to the emitter of the third transistor _TR3 . The base of the third transistor _TR3 is connected to the booster selector switch 8 via bleeder resistors _R7 and _R8 , and the collector is connected to the power supply +B via the other end of the capacitor 11 and a resistor _R6 . There is. In FIG. 2, the level detection circuit 9 in FIG. 1 includes a first transistor TR ₁ and its peripheral circuits, a diode D ₁ , capacitors C ₂ and C ₃ , resistors R ₄ and R ₅ , and a second transistor.
TR ₂ etc. correspond to this, and the switching circuit corresponds to transistor TR ₃ .

Next, the operation will be explained. First, in a weak electric field area, the booster changeover switch 8 is turned on in order to operate the booster 3 to amplify the radio frequency signal from the antenna 1 and supply it to the tuner 4. Therefore, since the voltage obtained by dividing the power supply voltage +B by the resistors R ₇ and R ₈ is applied to the base of the third transistor TR ₃ , the third transistor TR ₃ is energized in the direction of conduction, but the conduction is not achieved. In order for this to occur, the second transistor TR ₂ must also be energized in the conduction direction. Although the electric field is now weak, if it is above a certain level, there will be little noise component mixed into the positive polarity video signal that is applied from the intermediate frequency circuit 6 to the base point of the first transistor TR ₁ via the terminal 12. Therefore, even if negative horizontal pulses are added, the level at the leading edge of the horizontal synchronizing signal does not drop much, so the conduction bias of the first transistor _TR1 becomes shallow and the voltage drawn to its collector is relatively small. In addition, the video signal period (other than the synchronization signal period)
In the first transistor _TR1, the base voltage is sufficiently high and the collector voltage is low. Therefore, the potential at point (a) does not rise much, and the second transistor _TR2 is turned off. For this reason, the third transistor _TR3 is also unable to conduct, and the capacitor 11 remains connected to the power supply voltage +B, and does not function at all. Therefore, high frequency components are not attenuated in the video circuit 7.

However, when the video signal level is low and a lot of noise is mixed in with a weak electric field, a lot of noise is also superimposed on the sync signal tip, and the sync signal tip level when adding a negative horizontal pulse is The first transistor
The base of TR ₁ is lower and the bias is deeper.
Therefore, the potential at point a increases, and this voltage
R ₄ , R ₅ and capacitors C ₂ , C ₃ smooth the second
It is applied to the base of the transistor TR ₂ and turns on the same transistor and the third transistor TR ₃ .
FIG. 3 shows the relationship between the voltage level at point a and the electric field strength.

That is, the electric field strength decreases, the amount of noise mixed in increases, and the level at point a decreases to E ₁ [second transistor TR ₂
When the voltage reaches the ON level], the second and third transistors TR ₂ are also biased in the conduction direction, so the second and third transistors TR ₂ and TR ₃ are turned on, and one end of the capacitor 11 is connected to ground. That will happen. In this state, the high frequency components of the video signal in the video circuit 7 are transferred to the capacitor 11.
is largely bypassed by As a result, although noise generally exists in high frequency components, this noise is suppressed and becomes less noticeable on the screen of the picture tube 15. In the case of a strong field that turns off the booster selector switch 8, the base of the third transistor _TR3 is grounded by the resistor _R7 , so the third transistor _TR3 is never turned on, and therefore the first and second transistors TR3 are not turned on. Capacitor 11 does not operate regardless of the bias state of TR ₁ and TR ₂ .

In the above-described embodiment, it is possible to provide the same effect by using other suitable means instead of the capacitor 11, and the booster 3 is simply shown as a block; Of course, it is also possible to include a combination of a VHF booster and a UHF booster.

As explained above, according to the present invention, when the noise component included in the video signal exceeds a certain level in a weak electric field area, the level of the high frequency component of the video signal in the video circuit is automatically reduced. This is extremely effective in avoiding the influence of noise.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of the essential parts of a television receiver embodying the present invention, FIG. 2 is a partial circuit diagram thereof, and FIG. 3 is an explanatory diagram thereof. 1... Antenna, 3... Booster, 4... Tuner, 5... Tuning device, 6... Intermediate frequency circuit, 7
...Video circuit, 8...Booster selection switch,
9... Level detection circuit, 10... Switching circuit, 11... High frequency component attenuation capacitor.

Claims (1)

[Claims for Utility Model Registration] (1) A television equipped with a booster that amplifies the signal caught by the antenna before supplying it to the tuner, and a booster changeover switch that switches the booster between an active state and a non-active state. In the digital receiver, the level of the high frequency component of the video signal in the video circuit is reduced by a signal corresponding to the operating state setting of the booster and a signal detecting that the noise component in the video signal is above a certain level. A television receiver characterized by being provided with means. (2) Utility model registration claim 1, characterized in that the signal responsive to setting the operating state of the booster is a power supply voltage led by the booster changeover switch to set the booster to the operating state. The television receiver described in Section 1. (3) The means includes a detection circuit that detects that the noise component in the video signal is above a certain level, and a switching circuit that operates when the output of this detection circuit and a signal corresponding to the operating state setting of the booster are simultaneously present. and a high frequency component attenuator connected to the switching circuit and the video circuit and working when the switching circuit is activated. (4) Claims for registration of a utility model, characterized in that the high frequency component attenuator is a capacitor coupled to an amplifier of a video circuit, and the other end of the capacitor is grounded when the switching circuit is activated. The television receiver according to item 3.