JPS5888972A - Dc component reproducing circuit - Google Patents

Abstract

PURPOSE:To obtain a DC component reproducing circuit which can completely be coincided the pedestal level, by sampling a part of the pedestal level of a video signal and subtracting the potential from the original video signal. CONSTITUTION:A video signal inputted from a terminal 36 is amplified at a transistor (TR) 31 and enters a differential operation amplifier 35 and an FET 32 through TRs 39, 40. On the other hand, a pulse for pedestal level sampling is applied to terminal 37 to operate the FET switch 32. The pedestal level sampled with the FET 32 is held at a capacitor 33 and an FET 34 and outputted from the source of the FET 34. The pedestal level held at the FET 34 enters the differential amplifier 35, where the subtraction with the original video signal is done and outputted as a video signal coincident with the pedestal level from a terminal 38.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical field to which the invention pertains The present invention relates to a television camera 2. TV show award machine,
This article relates to a DC regeneration circuit used for signal processing in television broadcast equipment, etc.

In the processing 1111 of conventional various types of television and video signals,
If the DC component is passed through a circuit where the DC component is lost, such as an AC amplifier circuit, and there is a signal level difference between each twin signal of the TV screen video signal, the electrical black level of each horizontal twin signal will not be constant. A phenomenon occurs. Therefore, in order to match this, it is common to regenerate the DC component by clamping the part (usually the pedestal part) that always maintains a constant level with respect to the electrical black level on the horizontal scanning twin pot to a certain constant potential. It is. FIG. 1 shows an example of such a conventional DC component regeneration circuit.

A television signal input from terminal 1 is amplified by F tuner transistor 2 and applied to capacitor 3. Since the amount of charge charged to the capacitor 3 differs depending on the level difference between each line of the Eirin signal, the pedestal level of the Toga twin becomes inconsistent.

It is necessary to discharge the nine charges that are charged to each twin and round it. The switching diode 4 and the transistor 6 perform this.

Synchronizing with the period indicating the pedestal level that exists during the horizontal blanking period of the video signal, a 2-amp pulse is applied to the terminal 5 to turn on the transistor 6, its collector potential goes down), and the diode 4 becomes conductive. Become. The charge stored in the rounding capacitor 3 is discharged, and its voltage level is approximately fixed at the collector potential of the transistor 6.

If this is returned for each horizontal blanking period, the voltage level of each horizontal scanning signal is almost unified to the collector potential of transistor 6, and the output terminal 7 outputs a TV signal with a regenerated DC component. is obtained.

Disadvantages of the Prior Art However, this conventional DC regeneration circuit for a pedestal clamp has the following drawbacks.

In other words, if there is an extremely large difference in the pedestal level between the lines that meet each other, the charge stored in the capacitor 3 will not be completely discharged when ll11 is discharged, and the charge will remain, resulting in a complete DC component. The drawback is that it cannot be played back. As a result, several horizontal twins are required to match the pedestal levels.

First, when the time of the pedestal portion during the horizontal layer line period is much shorter, the clamp period must follow accordingly, and the discharge of the capacitor 3 becomes incomplete.

Therefore, in this case as well, sufficient DC component regeneration is not performed.

Purpose of the Invention The present invention has been made in view of the above points, and it is possible to completely scan the pedestal level even if there is a large difference in pedestal level between adjacent lines, or even if there is not enough time for the pedestal level portion during the horizontal scanning period. The purpose of this invention is to provide a DC regeneration path that can match the pedestal level to the pedestal level.

Structure of the Invention The present invention provides a sample-and-hold circuit that samples a part of the pedestal level during each horizontal blanking period of a television video signal and holds that potential for one horizontal scanning period, and nine held potentials thereof. It consists of a subtractor that subtracts the signal from the original TV set.

Embodiment The principle of operation of the DC regeneration circuit according to the present invention will be explained with reference to FIG.

A television video signal is input to terminal n. The pedestal level of each scanning line is indicated by a point m. This Eirin signal song is input to a sample hold circuit 21 and a subtracter n.

A sampling pulse n is input from the terminal arm. This pulse nail must have a phase that allows it to sample the pedestal portion of the input video signal 260 pack pouch. This sampling pulse γ is applied to the sample bold circuit 21. The hold waveform 4 thus obtained has a round shape, with only the pedestal fluctuation of the Eirin signal being extracted. If this is subtracted from the original Eirin signal portion using the subtractor n, the Eirin signal 4 without any pedestal fluctuation is obtained at the output terminal portion.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the DC component regeneration circuit of the present invention will be described in detail using the above-mentioned principle with reference to the drawings.

Figure 183 is an embodiment of the present invention. The input signal from the terminal arm is connected to the transistor 11Kj:1.
The signal is amplified by 1 and passes through the transistor 39 and the differential operational amplifier and the FIT switch 32, respectively. terminal 3
A pulse for pedestal level sampling is applied to 7 to open and close the FIT switch 32. The nine pedestal level sampled by the FliiT switch 32 is the capacitor 33! The transistor ω at ζζ is for impedance conversion with low output resistance, and the switch 32 is opened to charge or discharge the ndenna blade at 9 o'clock. Then, a new potential is set at 33.

The pedestal level held by the FIT u is input to the differential operational amplifier 35, where it is subtracted from the original television video signal and output from the terminal as a television video signal with a matching pedestal level. be done. In addition,
The transistors are rounded to compensate for the nine DC level differences caused by the transistors.

Other Embodiments Figure 4 shows other embodiments. This is the third
In place of the differential operational amplifier structure of the embodiment shown in the figure, F
It is possible to use a JILT differential amplifier as a precedent.

The differential amplifier is constructed as FIT44.45. 44
is amplified by a transistor 41 and is then amplified by 46 k) DC
A level-shifted television 1 video signal is input. The FIT 45 constitutes a hold circuit together with the stupid conductor +43 that constitutes the differential amplifier.
The pedestal potential sampled by the FFIT 42 is held together with the resistor 943. Therefore, there is an advantage that the holding PET 34 shown in FIG. 3 can be omitted.

Effects of the Invention Conventionally, a sufficient lamp pulse width (1-2 voice seconds) was required to fully operate the DC component regeneration circuit of the pedestal clamp Wi, but in the present invention, a narrow A pulse width (for example x
It works well even in seconds). In the DC component regeneration circuit, if the level difference between adjacent horizontal scanning signals is large, it will take several hours for the pedestal levels to completely match, but in the present invention, As long as the subtractor is not overloaded, the pedestal level will ring on a match. When using a differential amplifier or a differential operational amplifier as a subtracter, these hexagonal tolerance values are generally sufficiently large compared to the pedestal level deviation, so this is unlikely to result in an excessive input. This is a very effective method, as it can completely regenerate the DC component without adjusting the pitch as long as the phase of the sampling pulse is in the correct position.

It should be noted that the above-described nine television video signal is a video signal that is processed within a general television receiver. If this video signal is the output of a video camera equipped with an M-tube, a solid-state image pickup device, etc., the optical black level will not match due to the loss of the DC component. The present invention can also be applied to this case. That is, the 51st
I! As shown in Figure 2, the DC component can be recovered by sampling the optical black level 51 between this type of video signal in exactly the same way as described above. .

[Brief explanation of drawings]

111 is a circuit diagram of a conventional pedestal clamp type DC component regeneration circuit, FIG. 2 is a rounded schematic diagram explaining the principle of the tatami mat of the present invention, and FIG. 3 is a DC component regeneration @J! An example is shown below. Schematic diagram, no. From Yumoto. A circuit diagram showing another embodiment,
FIG. 5 is a schematic diagram of a video signal of the imaging device. Envy, 50... Lost DC portion of TV digital video signal, 27... Sampling pulse, 4...
...Regenerated video signal of DC component, valley...
Temple held clamp level, (capital)...
...Pedestal part, 32.42...FFIT for switching. Feather, 43...condenser for hold, recitation...
・PIT for hold. 35...Differential operational amplifier, 1.45...FIST for differential amplification. 51...Optical black level. Figure 1 Figure 2 Figure 3) 7 Figure 4 Figure 5

Claims (1)

[Claims] The optical black level or pedestal level of the pack pouch portion of the TV signal is not consistent between the two signals obtained by horizontal scanning due to the loss of the DC component. and means for holding the sampled potential for one horizontal scanning period and subtracting it from the television video signal, and regenerating the DC component of the television video signal. A DC component regeneration circuit featuring: