JPS5919508Y2 - VIR signal removal circuit - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a VIR signal removal circuit.

Overseas broadcast channels have a VIR signal (Vertical Interval) on the 19th H of each field.
There is a channel that inserts the reference signal).

As shown in Fig. 1, the VIR signal is composed of a chroma reference signal C, a luminance reference signal Y, and a black reference signal B. The VIR signal is detected by a VIR detection circuit, and the gain of the color signal is calculated by combining the luminance reference signal Y and the chroma reference signal B. The phase of the color signal is determined by the reference signal C, the phase of the color signal is determined by the chroma reference signal C, and the gain of the luminance signal is determined by the luminance reference signal Y and the black reference signal B.
Each is adjusted accordingly.

On the other hand, when recording and playing back NTSC broadcast signals,
Normally, the color signal is low-frequency converted so that it has an interleaving relationship with the low-frequency luminance signal, and the carrier of one field is inverted and recorded every LH (H is a horizontal scanning section), and after playback, the carrier is used again as the original. At the same time, the low-frequency color signal including the low-frequency luminance signal is converted back to a high-frequency signal and is input to the comb filter.

In the comb filter, the subcarrier of the NTSC signal is 1H.
By taking advantage of the fact that the signal is inverted every time, the original signal and the inverted output of the 1H delayed output are averaged to simultaneously remove the low-range luminance signal component that is in an interleaving relationship and eliminate the cross-stroke component with the adjacent track. ing.

Therefore, a comb filter installed in a VTR that records NTSC color signals by converting them to low frequency halves the amplitude of the chroma reference signal C when recording and playing back NTSC broadcast signals including vIR signals. do.

Therefore, the deformed VIR signal not only cannot serve as a reference signal, but also disturbs a normal image.

Therefore, a VIR signal removal circuit for eliminating the VIR signal is conventionally provided in a VTR that derives the reproduced output through a comb-shaped filter.

FIG. 2 shows a block diagram of a conventional VIR signal removal circuit, in which the clamp output of the clamp circuit 1 to which the video signal a is input is controlled by one person, and the black level output C of the black level setting circuit 2 is controlled by one person.
, and count the (horizontal) synchronization separation output d of the video signal a derived from the synchronization separation circuit 3 to calculate V.
The sampling output e of the 19H sampling pulse generation circuit 4 for detecting the multiple scanning section of the IR signal is input to the switching circuit 5 as a control input.

The switching circuit 5 selects the black level output C in place of the clamp circuit upon generation of the sampling output e, thereby deriving a switching output f from which the VIR signal is removed.

The circuit connection between the conventional clamp circuit 1 and black level setting circuit 2 will be further explained below with reference to FIG.

As shown in the figure, the clamp circuit 1 connects the DC voltage to the first resistor R1.
and the second resistor R2, and the second resistor R2 on the ground side
By arranging a first capacitor C1 for charging and discharging in parallel with and connecting the first diode D1 in the forward direction from the connection point G of the sheet resistances R, , R2 toward the video signal line,
The synchronization tip of the video signal is set from the potential of the connection point G to the
It is clamped to a potential obtained by subtracting the voltage drop of the diode D1 and inputted to the switching circuit 5. In addition, in the black level setting circuit 2, a variable volume VR is arranged to divide the DC potential between the slider and the ground. By connecting a second capacitor C2 for charging and discharging between them, the slider is adjusted so that the slider potential is at the pedestal level and -, and is inputted to the switching circuit 5 as a black level output C.

Note that the third capacitor C3 arranged in the video signal path is a capacitor for blocking DC components.

The present invention proposes a new and effective VIR removal circuit that makes it possible to reduce the number of circuit components in the conventional example by using the voltage at the dividing point a as a black level output. It is something.

The present invention will be explained below according to an embodiment shown in FIG.

In this embodiment, the first resistor R1 and the second resistor R1 divide the DC voltage.
The potential at the connection point G of the resistor R2 is set to the pedestal level, and the diode D1. A clamp circuit is constructed by making the voltage drop in the forward direction of D2 match the pedestal level and the potential difference at the synchronization tip, and the potential at the connection point G is inputted to the switching circuit 5 as a black level output C.

Therefore, according to the circuit of this embodiment, when the extraction pulse e is not generated, the first and second resistors R1 and R2, the cascade-connected diodes DI and D2, and the first capacitor C1 for charging and discharging are clamped. When the sampling pulse e is generated, the potential at the connection point G between the first and second resistors R1 and R2 is derived from the switching circuit 5.
It is derived in place of the R signal.

Therefore, according to the circuit of this embodiment, since the clamp circuit also functions as a black level generating circuit, it is possible to reduce connection work and the number of parts, which is highly effective.

It should be noted that there is no difference in effectiveness whether the circuit of the present invention is provided in the recording side circuit or the reproduction side circuit of a video tape recorder.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the waveform of the VIR signal, FIG. 2 is a block diagram of a conventional circuit, FIG. 3 is a circuit diagram of the main part thereof, and FIG. 4 is an example of an implementation circuit of the present invention. Explanation of main drawing numbers 1... Clamp circuit, 4...
...19H sampling pulse generation circuit, 5...Switching circuit, G...Connection point, b...
- Clamp output, e... Sampling pulse (sampling output), C... Black level output.

Claims (1)

[Scope of utility model registration request] In a videotape recorder that records a color signal in an interleaving relationship with a low-frequency luminance signal and converts it to a low frequency range, it also separates the color signal through a comb filter during playback and reconverts it to a high frequency range. a clamp circuit that sets the connection point of the connection point to a black level potential, and makes the forward voltage drop of a diode connected in the forward direction from the connection point to the video signal line equal to the potential difference between the black level and the synchronization tip;
The clamp circuit includes a 19H sampling pulse generation circuit that counts horizontal synchronizing signals and generates a sampling pulse for VIR signal detection, and a switching circuit that derives a black level output instead of a clamp output in response to the generation of the sampling pulse. A VIR signal removal circuit characterized in that a potential at a connection point of is inputted to the switching circuit as a black level output.