JPS62154993A - Signal processing circuit - Google Patents

Abstract

PURPOSE:To reduce the generation of beat disturbance by performing the balanced modulation and addition of a signal passed through a circuit which performs clipping at an optional level with mutually 90 deg. out-of-phase subcarriers. CONSTITUTION:When a proper control voltage is applied to a terminal 16, currents (i) having the same value flow to the collectors of transistors (TR) Q5, Q6, Q8, and Q9 on condition that the hFE difference of a TR 9 is ignored (provided that R1=R2=R7=R8). Therefore, a potential (VRef+iR4) is developed at the intersection of resistance R3 and R4 and a potential (VRef-iR5) is generated at the intersection of R5 and R6. On the other hand, a potential (VRef+i(R3+ R4)) is developed at the collector of the TR Q5 and a potential (VRef-i(R5+R6)) is generated at the collector of the TR Q8. The former voltages are used as limit voltage Vcu2 and Vcd2 of an amplitude control circuit 12 and the latter voltages are used as limit voltages Vcu1 and Vcd2 of an amplitude limiting circuit 11 to obtain desired amplitude limiting effect.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a signal processing circuit for a color video camera, etc.
In particular, the present invention relates to a circuit that effectively limits the amplitude of an excessive carrier color signal level of a composite video signal obtained at an encoder output without causing phase distortion or luminance distortion.

[Conventional technology]

As an example of the conventional color video camera signal processing J1 old TO 11 route, Nishi et al. = "IC for color video cameras" Naru 1 Naru Technical Report Vol. 28, No. 2, April 1982, pp. 183-192; Alternatively, there is one described in "Hitachi Consumer IC Data Book: vrxHJrc r Video Camera 2 IC", February 1980, pages 9'5 to 128.

[Problem that the invention seeks to solve]

The conventional signal processing circuit described above is a signal processing circuit that effectively limits an excessive color signal level that exceeds the maximum white level of a composite video signal obtained at the output of the two-second circuit, that is, the output of two color video camera circuits. The circuit has not been given due consideration and has the following problems. Well-known: First, in television broadcasting, the amplitude of the carrier wave to be broadcast is modulated using a composite video signal, but when the brightness of the subject is high and the signal is thick, the amplitude of the carrier wave decreases, using a so-called negative modulation method. is taking. Therefore, from the viewpoint of i purity of modulation characteristics, it is specified that the carrier wave is left up to j2.5% of the maximum value (synchronization part) for the brightness signal of the brightest white object. When a carrier chrominance signal is combined with this luminance signal, if its amplitude range becomes too narrow, overmodulation will occur, making it impossible to provide sufficiently satisfactory transmission characteristics. Therefore, as shown in the luminance order color bar signal waveform example shown in FIG.
It is stipulated that the limit shall not be exceeded. The carrier color signal level increases as the saturation of the color increases, and even if the color has the same chromaticity, as the luminance increases, the carrier color signal becomes sharper. Due to the above, the color television signal in FIG. 3 is expressed by the following formula.

Ey: Luminance signal ER4y: Red difference signal g, -gY: Blue difference signal f,: Subcarrier frequency As shown in this equation, the level diagram is On the other hand, as seen in recent years with the spread of home-use power cameras and home-use VTR-integrated video cameras, it is possible to not only record broadcast signals but also record the signals yourself.
Recorded on J'TR.

A lot of attention has also been paid to regeneration. When the composite video signal is recorded and played back on a home VTR in this way, even within the limited range of the carrier color (K), for example, the reproduced image will be a highly saturated yellow, a red flower, a blue sky, etc. Beat interference may appear in brightness when the carrier chrominance signal is converted to a low frequency and the brightness signal is FM-modulated for recording and reproduction.

This is caused by cross-modulation between chromaticity signals, and occurs in areas with high chroma and high brightness, which is a visually unpleasant disturbance. Conventionally, when recording and reproducing on FTH, the above-mentioned disadvantages occur. A simple countermeasure for this is, for example, the composite image shown in Figure 3.

It is considered and often adopted to clip and record levels exceeding a predetermined level (V,) shown in the image signal waveform.This reduces beat disturbance, but only one side of the carrier color signal is clipped. As a result, a DC component is generated and the brightness reproduction is deteriorated, or a hue change is caused in the carrier color signal and the color reproduction is deteriorated, or magenta is lower than the clip circuit /I/(Vc) shown in FIG.

Red part 2 etc. cause inconveniences such as no effect being obtained. It is also possible to limit the amplitude of a color signal with high saturation, that is, a high carrier color signal level, to a predetermined level at the stage of the carrier color signal before mixing the luminance signal and the carrier color signal. Due to unbalanced characteristics, clipping characteristics, etc., it is difficult to clip the + side and the - side in a well-balanced manner, resulting in a change in the phase characteristics of the carrier color signal and a disadvantage that color reproduction deteriorates.

The present invention improves the above-mentioned conventional disadvantages, that is, effectively limits the amplitude of the carrier color signal without deteriorating the luminance reproduction, 9 hue reproduction, etc., and improves the composite image quality.

The purpose of this invention is to reduce the occurrence of the above-mentioned beat disturbance that occurs when a signal is input to a VTR and recorded.

[Means for solving problems]

The above purpose is the red color difference (x-y) generated by the camera circuit.
, the baseband of the blue color difference (B-y) (e.g. band: 5
This is achieved by installing a circuit that can clip the color difference signal at any desired level in each path, and adding the signals passing through the circuit using subcarriers with a phase difference of 90'. Ru.

[Effect]

The clipping circuit described above can process signals in a low frequency region. Therefore, the amplitude value of the baseband color difference signal is well limited to a desired level. As a result, after balanced modulation of each of the above color difference signals with a subcarrier, the vector composite wave generated by adding them, that is, the excessive amplitude of the carrier color signal, can be effectively reduced to the desired level, and the above phase distortion or This can be restricted without causing any inconvenience such as affecting brightness reproduction.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. The embodiment shown in FIG. 1 shows an example of a circuit configuration centered on an encoder circuit for obtaining a composite video signal. A luminance signal and two color difference signals generated by an in-camera signal generation circuit are input to terminals 1 and 2.3, respectively. Terminal 7 is a clamp pulse application terminal, and terminal 8 is a blanking pulse application terminal. The luminance signal input to terminal 1 is clamped by clamp circuit 4, and white clipped by signal processing circuit 9.
After signal processing such as black clipping and blanking processing, the signal is input to the mixing circuit 10. On the other hand, the color difference signals R-4, B-
Y is input to terminals 2 and 3, respectively, at the upper level ratio. After the RY color difference signal inputted to the terminal 2 is clamped by a clamp circuit 5, an amplitude limiting circuit 11 limits the upper and lower amplitude values of the color difference signal exceeding a predetermined level. The color difference signal B-Y is mixed with a burst flag pulse of 6't 1 m during the blanking period, inputted to the terminal 3, and similarly clamped by the clamp circuit 6 and output to the amplitude limiting circuit 1.
The amplitude is limited in 2). The color difference signal (R-y) with limited amplitude and the color difference signal (n-y) with limited amplitude and H7Jn of burst flag pulses are connected to terminals 17 and 18, respectively, and are out of phase with each other. 90'
Different subcarriers (NTSC: f = 158M11z
) are balanced-modulated in balanced modulation circuits 19 and 20, and then vector-combined in an adder circuit 21 to generate a carrier color signal [1 to which a burst signal is added. The carrier color signal is passed through a bandpass filter (e.g. j = 5.SBMIh±0.5
After band-limiting by MHz), the signal is input to the mixing circuit 10, where it is synthesized with the luminance signal input from other terminals and the synchronization signal input to terminal 23, and output to terminal 2.
4, a composite video signal with limited overcarrying chrominance signal amplitude is obtained. Terminals 15 and 14 are amplitude limit voltage application terminals, and are supplied from the amplitude limit voltage generation circuit 15. j “Terminal 1
The limit level can be varied by the DC control voltage applied to 6.
Set, 7.

Can be determined. The amplitude limit level is set to an appropriate value from the viewpoint of the above-mentioned occurrence of beat disturbance; it is good.

According to this embodiment, since the amplitude limiting process can be performed on the baseband color difference signal, that is, the low frequency region (DC ~ 500KIIz), the frequency characteristic KEEL of the circuit is hardly affected, and the amplitude limiting process can be performed satisfactorily in terms of waveform processing. . In addition, K limits the temporal amplitude of the color difference signal in one direction,
It is possible to effectively limit the excessive amplitude level of the carrier color signal after balanced modulation without generating any phase error.

FIG. 2 shows an amplitude limiting circuit 11 which is the main part of the embodiment shown in FIG.
．． 12 and an amplitude-limited voltage generating circuit 15 are shown. The amplitude limiting circuit 12 is shown in a block diagram because it has the same circuit configuration as the amplitude limiting circuit 11 in the figure. A color difference signal waveform diagram is shown in the case of the brightness order color bar signal shown in FIG. VBIll is a clamp potential, and the numerical values written corresponding to each color represent the composite video signal in Fig. 3,
6, that is, the value corresponding to level 1 of the luminance signal (black to white) of the luminance-ordered color bar signal described above. Transistors Q1 and Q2 are applied to the base of Q2 in the lower clip circuit, that is, to the terminal 141. A voltage greater than or equal to that voltage is sensed at the common emitter and is input to the base of transistor Q3. Next, the transistor Q5tQ4 is an upper clip circuit, and a voltage lower than the voltage applied to the base of Q4, that is, the terminal 142, is detected at the common emitter. Therefore, by applying desired potentials Vcws r Vcd+ in the figure to the bases of transistors Q2 and Q4, amplitude values exceeding a predetermined value can be limited and detected. On the other hand, the amplitude limiting voltage generation circuit is connected to the resistor R1+J? t r Rt +
Rs + ) transistor Q5. Q6. Q7. QB, Q
9 and resistors Rs and Ra
, Rs, R6, and the reference voltage source (J'Rg7'
). If an appropriate control voltage is applied to terminal 16, transistor Q5. The same current t flows through the collectors of Q6゜Q8 and Q9 (however, R1-7?2-Ry
-R8). Therefore, a potential of (V□f+tRa) is generated at the intersection of resistors R3 and Ra, and a potential of (VB tl's) f- is generated at the intersection of Rs and R6. On the other hand, the potential of (V□f+t(Rs+R4)') at the collector of transistor Q5 is q
For the collector of (V□f-i (B54-Rh))
potential is generated. The former potential is set to the limiting voltage Vcu z + F of the amplitude control circuit 12, 1. If x is given as the limiting voltage Vcut + Vcdt of the amplitude limiting circuit 11, a desired amplitude limiting effect can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, the composite video signal generated by the camera circuit is converted to VT)? To limit only the amplitude value of a carrier color signal that is so excessive as to cause beat disturbance due to the variation between luminance and chromaticity, without causing any adverse effects such as phase distortion or luminance distortion, when inputting and reproducing the wiring. It is possible to obtain a good reproduced image with reduced beat disturbance.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
This figure is a circuit diagram showing a specific example of an amplitude limiting circuit and an amplitude limiting voltage generating circuit which are the main parts of FIG. 1, and FIG. 5 is a waveform diagram showing a luminance-ordered color bar composite video signal. 1.--Brightness signal input terminal 2...
......R-I' color difference signal input terminal 3...
......B-Y color difference signal input terminal N, 12.
... Amplitude limiting circuit 16 ...... Amplitude limiting voltage generating circuit 19.2
0...Balanced modulation circuit

Claims (1)

[Claims] An amplitude limiting circuit that limits the amplitude to a desired level is installed in each signal transmission path of two different baseband video signals (for example, a red difference signal and a blue difference signal), and each signal whose amplitude is limited by the amplitude limiting circuit A carrier color signal whose excessive amplitude is effectively limited to an appropriate value is obtained by balancedly modulating subcarriers having different phases (for example, 90 degrees) using the video signal, and then adding them (vector synthesis). A signal processing circuit characterized in that: