JPS59188281A - Television receiver with ghost eliminating device - Google Patents

Abstract

PURPOSE:To obtain a correct ghost reference waveform and to perform accurately ghost detection by inhibiting a video intermediate frequency AGC circuit from making a response only almost at the leading edge of a vertical synchronizing pulse. CONSTITUTION:A switching control circuit 2 which turns on and off by a control signal generating circuit 5 is added to a video detection AGC circuit 4. The AGC circuit 4 consists of transistors (TR) Q1-Q3, etc., and controls the gain of a video intermediate frequency amplifier A or tuner B according to the level of a signal inputted from a video detecting circuit 1. A switching circuit 3 provided to the control circuit 2 is turned on only almost at the leading edge of the vertical synchronizing pulse for detecting a ghost by a control signal C outputted from a control signal generating circuit. This on operation increases the filter time constant of the AGC circuit 4 to delay the response of AGC, preventing the variance of the waveform of the vertical synchronizing pulse nearby the leading edge.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates to a television receiver equipped with a ghost removing device that automatically removes ghosts.

Conventional configuration and its problems In a conventional television receiver equipped with a ghost removal device, a method is known in which the leading edge of the vertical synchronization pulse is used as a reference waveform to obtain ghost information. There is. This detection method will be briefly explained.

FIG. 1 shows a waveform diagram near the vertical synchronization pulse of a television signal. In Figure 1, PH is the horizontal synchronization pulse, PE is the equivalent pulse, PV is the vertical synchronization pulse, and T.
T3 is the equivalent pulse period, T2 is the vertical synchronization Hals period'
LBL is blanking level, LB is black level, LW
indicates the white level, and L2 indicates the zero carrier level.

As can be seen from the waveform of FIG. 1, the vertical synchronization pulse Pv appears after the equivalent pulse period T. FIG. 2 is an enlarged view of the state near the vertical synchronizing pulse Pv when there is a ghost signal. Figure 2 (a) shows the normal vertical synchronization pulse waveform, and Figure 2 (b) shows the ghost waveform of ma), which is a single positive ghost with a delay period τ (sec). , is the ghost vertical sync pulse.

FIG. 4(Q) is a composite waveform of the waveform in FIG. 1(a) and the waveform in FIG. 4(C), in which a so-called ghost signal is superimposed.

If a signal like this in Figure 2 (0) is obtained, the presence of a single positive ghost at a distance τ (seo) from the leading edge of the vertical synchronization pulse means that the waveform in Figure 2 (0) is obtained. - Waveforms in Figure 2 (-) - Figure 2 (b)
) is clearly obtained from the waveform of In fact, one method for determining ghosts is to use the leading edge of the vertical synchronizing pulse as a reference, and to determine based on the impulse responses (differential waveforms) before and after the leading edge. In the case of Fig. 2(e), a positive impulse is obtained at a distance of τsec from the leading edge of the vertical synchronizing pulse, so a positive ghost is detected with a delay of τSeQ from the leading edge of the vertical synchronizing pulse. It is determined that there is. Roughly speaking, when there are multiple ghosts as shown in Figure 3(b), the impulse has the waveform shown in Figure 3(11), with a positive ghost of +2 μsec, a positive ghost of +3 μsec, a negative ghost of +5 μsec, and the following. The ghost level is proportional to the amplitude of the impulse.

The automatic coast removal device detects the level and time delay (or advance) of the positive ghost and negative ghost, and cancels the ghost by adding a signal of opposite phase to the ghost at that time.

The above is a case where the normal signal and the ghost signal are ideally combined, and if there is a normal ghost, the waveform shown in FIG. 2(C) cannot actually be obtained from the video detection output. This will be explained specifically. FIG. 4(a) shows a composite signal waveform of the signal of FIG. 2(&) and its ghost waveform of FIG. 4(b). The problem will be explained while comparing the waveforms in FIG. 4(a) and FIG. 2(C).

−τ. There is a vertical sync pulse front at -τ, and a ghost signal rises at -τ, Figure 4 (A).
, va is the trough pressure of the vertical synchronizing pulse, which is maintained at a stable DC potential by the AGC circuit of the video intermediate frequency amplification circuit. This is the rising potential of the ghost signal starting from V&'it-τ.

A: The video signal momentarily increases due to the ghost signal.
The GC circuit makes a judgment and works to lower the ghost signal to the level of VA. Therefore, the signal is deformed by the time constant caused by the filter of the AGC circuit, as shown in the waveform shown in FIG. 4 (-).

The problem with the waveforms from Figure 2 ((1) to Figure 4 (Ik) is that (1) also has a ghost signal during the periods -τ and ~τ, as shown in Figure 4 (B). Because of the deformation, the impulse is the fourth
As shown in Figure (b), an impulse a (normal) is obtained at t-τ, and a signal b is obtained at t=τ1 to τ2 (discriminated as a negative ghost). For this reason, the automatic ghost removal device judges that there is a negative ghost based on the information b, and incorrectly performs ghost processing.

(2) Furthermore, if the time constant of the filter of this AGC circuit is increased, an ideal signal for automatic ghost removal can be obtained as shown in Fig. 2(e), but on the other hand, ■ The response of the AGC circuit to fluctuations is extremely slow (on the order of seconds).

(2) Problems arise such as the flutter characteristics of the AGC circuit are extremely poor (the response characteristics of the AGC are poor even when there is even a slight disturbance from a car, and the TV receiver is not at a practical level).

The reason why the ghosts described so far are limited to positive ghosts as mentioned above is that only when the ghosts are outside the top of the vertical periodic pulse (above va in Fig. 4 (A)), the AGC operation is performed in this way. To become.

Among the tops of the vertical synchronization pulses (in Fig. 4(a), VEL
If the ghost signal affects only the lower part), the ghost waveform will not be deformed by the anus, and ghost detection will be performed normally.

Purpose of the Invention This invention prevents the image intermediate wave AGC circuit from responding and deforming the waveform near the vertical synchronization signal when a ghost signal is superimposed on an input signal, especially when a positive ghost is superimposed on the input signal, and corrects the ghost signal. It is an object of the present invention to provide a television receiver with a ghost removal device that can obtain a reference waveform for detection.

Composition of the Invention The television receiver with a cost removing device according to the invention has the following features:
The switching circuit is operated only near the vertical synchronization signal where ghosts are detected, and the filter time constant of the intermediate frequency AGC circuit is increased to prevent waveform deformation near the leading edge of the vertical synchronization pulse. This is to ensure that detection is performed normally.

DESCRIPTION OF THE EMBODIMENTS FIG. 5 shows a circuit diagram of the main parts of a television receiver equipped with a ghost removal device according to an embodiment of the present invention. In FIG. 5, 4 is a video intermediate frequency AGC circuit, and its operation will be explained below. In the video detection circuit 1, video pressure and a synchronous negative signal are applied to the base of the transistor Q3. When the video signal becomes larger, the top of the vertical synchronizing pulse drops below the potential of V□, turning off transistor Q3 and turning on transistor Q2, so transistor Q□ turns off! l), the charge stored in the capacitor C is transferred to the transistor Q2. It is discharged through Q4. As a result, the potential of vA decreases, and the gain of the video intermediate frequency amplifier 8 or tuner B is lowered to reduce the video signal. The relationship between the potential of VA and the gain of video intermediate frequency amplifier A or tuner B is shown in FIG.

Conversely, when the video signal becomes small, the transistor. 3 is on, transistor Q is off, transistor. is turned on, the capacitor C is charged through the transistor Q, and V
The potential of A increases, and the gain of video intermediate frequency amplifier A or tuner B is increased to increase the video signal.

2 is a control circuit which is the main part of this invention.

The switching circuit 3 is turned on only near the leading edge of the vertical synchronization pulse for detecting ghosts by the control signal C output from the control signal generation circuit 5, and the capacitor C2 is connected to the capacitor C of the filter time constant of the video intermediate frequency AGC circuit 4. By connecting them in parallel and increasing the filter time constant, the response of the AGC is delayed to prevent the waveform near the leading edge of the short-plane synchronization pulse from changing, so that ghost detection is always performed normally. . R□ and R2 are resistances.

A specific circuit example of the switching circuit 3 in FIG. 5 is shown in FIG.
As shown in the figure. In FIG. 7, the control signal C (negative pulse) is applied to the transistor Q4 only during the ghost detection period.
is turned on, and transistor Q5. Turn on one of Q6 to connect capacitor c2 to capacitor c1. Capacity C
When the potential of capacitor C2 is higher than the potential of VA, transistor Q6 is turned on, and conversely, when the potential of capacitor C2 is lower than the potential of vA, transistor Q5 is turned on.

In addition, during periods other than ghost detection, control signal C
When transistor Q4 is off, transistor Q5.
By turning off Q6 and disconnecting capacitor C2 from capacitor C, the video intermediate frequency AGC circuit 4 returns to normal operation. R37?
Ishi R5 is a resistor.

The above operation will be explained using FIG. 8. The control signal C in FIGS. 5 and 7 is shown in FIG. 8(a). This control signal C is a negative pulse during time t=τ3 to τ4, and
Leading edge t=τ of the vertical synchronization pulse in figure (b). Let us assume that there is a relationship as shown in the diagram.

As shown in FIG. 4, the broken line
It gradually decreases during the period of ~τ2. In FIGS. 5 and 7, when the control signal of FIG. 8(a) is added, t=τ3~τ
For the 40 period only, the capacitance C is added to the filter capacitance C□ of the conventional AGC.
2 is connected and the time constant is increased, so AGC is t-τ
Even if a positive ghost signal is superimposed during the period 3 to τ4, the 8th
The video intermediate frequency AGC circuit 4 returns to normal operation at t>τ4 when the desired signal waveform, the solid line X2 in FIG. 8(b), is obtained instead of the broken line X in FIG. 8(b). Therefore, with the time constant of the conventional AGC, the potential vA in FIGS. 5 and 7 is t-τ, as indicated by the broken line Y in FIG. 8(C), and thereafter, charging and discharging are repeated. ), which lowers the gain of video intermediate frequency amplifier A or tuner B.

On the other hand, in the case of the embodiment, the gain does not change as shown by the solid line Y2.

In the automatic ghost removal device, it is sufficient to obtain normal signals from the leading edge of the vertical synchronization pulse by 1 [H] to 4 [H], so the pulse width in Fig. 8(a) is also 2τ3.
~τ4 should be about 1 [H] (635μ9eO) or more.

During this time, even if the filter time constant of the AGC is increased, the operation of the AGC as a television receiver will not become unnatural.

As a result of this configuration, even when a positive ghost is superimposed, the video intermediate frequency AGC circuit can be prevented from responding only near the leading edge of the vertical synchronization pulse, and as a result, a correct ghost reference waveform can be obtained. Therefore, ghost detection can be performed accurately, and ghost removal can be performed accurately and easily without affecting the normal AGC operation of the television receiver.

Effects of the Invention As described above, according to the television receiver with the ghost removal device of the present invention, the normal AGC of the television receiver can be
A correct ghost reference waveform can be obtained without affecting operation, and therefore ghost detection can be performed accurately.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram showing the vicinity of the vertical synchronization signal of the television signal, FIG. 21 t8), (b), (C), and FIG. 3 (a). (b) is a waveform diagram showing the waveform and ghost detection method when a ghost is superimposed when the intermediate frequency AGC circuit does not respond.
A waveform diagram showing the waveform and its differential waveform when the circuit responds; FIG. 5 is a circuit diagram showing the configuration of an embodiment of the present invention; FIG. 6 is a characteristic diagram of gain versus VA potential; FIG. Fifth
Specific circuit diagrams of the main parts of the figure, Figures 8 (R) and (b). (e'l is a waveform diagram of each part for explaining the operation of the embodiment. l...Video detection circuit, 3...Switching circuit, 4
...Video intermediate frequency AGC circuit, 5...Control signal generation circuit. Fig. 1 ((Il-connection Fig. 2)

Claims (1)

[Claims] a video intermediate frequency AGC circuit; a control signal generating circuit that generates a pulse for a predetermined period near the leading edge of a vertical synchronizing pulse; and a filter time constant of the video intermediate frequency AGC circuit during the generation period of the output pulse of the control signal generating circuit. A television receiver equipped with a ghost removal device, comprising a switching circuit that increases the size of the vertical synchronization pulse to prevent waveform deformation near the leading edge of the vertical synchronization pulse.