JPS6022889A - Chrominance signal processing circuit - Google Patents

Abstract

PURPOSE:To improve the color picture quality at reception of a weak electric field by adopting the ACC control by peak ACC detection in demodulating and reproducing a color television signal to reduce color noise. CONSTITUTION:A composite color television signal subject to video detection is separated for a chrominance carrier signal at a band pass filter 6 and the result is applied to an amplifier 13. The burst signal component is amplified by the amplifier 13, fed to a clip circuit 14, where only the superimposed noise component is clipped. The clipped signal is fed to a burst gate circuit 10 via an ACC amplifier 7, where the burst part is extracted and the result is subject to peak detection at an ACC detector 11. An output signal of the ACC detector 11 is charged in a capacitor 12 and a voltage across the capacitor 12 is used as a gain control signal of the ACC amplifier 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color signal processing circuit ## that can be used for demodulating and reproducing color television signals in color television receivers or similar color television receivers.

Conventional Structure and Problems Therein FIG. 1 shows a block diagram of the manufacturing process related to color signal processing of a conventional color television receiver. In FIG. 1, a signal received from antenna 1 is transmitted to tuner 2. The signal is synchronously amplified in the VIF amplification stage 3 and detected in the video detection stage 4 to become a composite color television signal. The composite color television signal is fed to a video amplifier 6 and to a one-band filter (B, P, F,) e - where the carrier color signal is separated. The carrier color signal is amplified by an AGO amplifier 7 and supplied to a -RY demodulator 8 and a BY demodulator 9. A signal is also supplied to the burst gate circuit 10 from the output of the ACC amplifier 7, and only the burst signal is extracted by the burst gate pulse applied to the conductor &11Q2L. The burst signal extracted by the burst gate circuit 10 is applied to the ACC detection circuit 11, where the amplitude of the burst is detected and a voltage proportional to the amplitude is applied to the capacitor 1.
20.Grow on both ends. This voltage Vc is supplied as a gain control voltage to the ACC amplifier 7 via a conductor 13.

As is well known, the ACC amplifier 7 adjusts the amplitude of the burst signal to A
The CE detector 11 detects the wave, and the DC voltage corresponding to its amplitude is output to the ACC amplifier 7. ! ) 1ltlJ is used as a control voltage, and if the amplitude of the burst signal is smaller than a predetermined level, the gain of the -Ace amplifier Y is increased, and on the other hand, if it is larger than a predetermined level, the gain fII is lowered to
The output amplitude at CCCC amplifier power is kept constant.

By the way, the signal strength of the signal that enters the receiver's antenna varies over a very wide range depending on the receiving environment and conditions.If the antenna input signal is large and clean, there is no problem, but when the input signal is weak, The signal, which has a low s/ ratio and is buried in noise, is demodulated and viewed. Fig. 2 shows an actual measurement example showing this related amount. In Fig. 2, the horizontal axis represents the electric field strength, and the vertical axis represents the input of the ACC amplifier 7.
2 is a graph schematically showing the relationship between peak values and In FIG. 2, the solid line indicates the amplitude of the -burst signal, which remains constant regardless of the magnitude of the electric field strength. On the other hand, the dashed line indicates noise (peak-to-peak value), and when the electric field strength is strong, - is almost ignored, but the electric field becomes weak (4).
This figure shows how the stone noise component increases.

Now, the gain control of the ACC amplifier is to adjust the gain to compensate for the increase or decrease in the burst amplitude and keep the output amplitude constant. Ideally, if the amplitude is constant, the output signal amplitude will be constant even if the electric field strength is weak, as shown by the solid line in FIG.

However, in this case, as shown in Figure 2, the weaker the electric field strength is, the more the noise N increases, and the signal that has decreased by 3/M is fully demodulated. The image becomes darker and the image quality deteriorates to 0. This tends to occur when a synchronous detector is used as the ACC detector, and to avoid this, a peak detector is used. That is, this principle will be explained using a simple waveform in FIG.

In FIG. 4, one waveform A schematically represents a burst signal when the noise component is negligible, and one waveform B represents its peak detected waveform. It is assumed that a capacitor is charged with this detection output to obtain a voltage Vc+ having a zopeak value. On the other hand, waveform C schematically shows the case where noise is randomly superimposed on the burst 11':'"'j. Waveform C also shows the detected output waveform. As shown in the figure, VC-noise is superimposed and Therefore, the peak bolded DC voltage VC2
becomes larger than Vc+. As a result, since the gain of the ACC amplifier is controlled by this Vc+ or VC2, it is better when noise is superimposed than when the noise can be ignored. - Decrease the gain of the ACC amplifier.

Therefore, when receiving a weak electric field, the colors become fainter than when receiving a strong electric field, which alleviates the difficulty in viewing due to color noise. That is, as shown by the broken line in FIG. 3, compared to the output amplitude (solid line) under ideal ice control.

Output amplitude becomes small in weak electric field.

However - in general, the waveform of noise is not uniform.

Depending on the received signal and the characteristics of the transmission system leading to the ACC amplifier, for example, the reproduced color in a weak electric field that you want to view may become too pale. Although it is desirable to have the level at point a' (dotted line) at electric field strength A in FIG. 3, there is a drawback that the level is reduced to one point, which is indicated by the broken line.

OBJECT OF THE INVENTION The present invention aims to improve the above drawbacks and to prevent the saturation of a reproduced image from dropping too much when receiving a weak electric field in a color signal processing circuit using a color ACC control circuit using a one-peak detection method. It is something to do.

Structure of the Invention The present invention includes a bandpass filter for extracting a carrier color signal from a color television signal, a bandpass amplification (b) path for band-amplifying the carrier color signal, and a detection circuit for detecting the amplitude of a burst signal. The control signal obtained from the output signal of this detection circuit is configured to control the amplification gain of the band-pass amplifier circuit, and the noise superimposed on the burst signal period of the output signal obtained by the band-pass filter is appropriately suppressed. After passing through a clipping circuit that clips at a certain level, the signal is supplied to the above-mentioned band amplification circuit.

DESCRIPTION OF THE EMBODIMENTS FIG. 5 is a diagram showing an embodiment of the present invention. In FIG. 6, the composite color television signal subjected to image IW detection is passed through a one-band pass filter 1, and the carrier color 411 is passed through a single band pass filter.
Separate the numbers and take them out. This carrier color Iha bow is one amplifier 1
3, as shown schematically in FIG. 6, an input signal such as waveform A is applied so that the burst signal portion as shown in waveform B is sufficiently larger than the maximum value of the color signal component during the scanning period. Amplify.

The output of the amplifier 13 is supplied to a clipping circuit 14, where it is clipped at the level shown by the broken line of waveform B or waveform C1. In other words, the burst signal No. 8 and the color signal are at a level that is not even close to this clip level.
Stubble. Therefore, the noise component superimposed on the signal is clipped at a constant level as shown in the waveform C. In waveforms C and D of FIG. 6, noise superimposed on the burst signal and the color signal is simply indicated by thin lines.

As shown in the waveform, the noise clipped signal is the fifth
As shown in the figure, the AGO amplifier 7 performs gain control amplification using the same principle as in the prior art, the Hurst gate circuit 10 extracts the burst portion, and the ACC detector 11 detects the peak. The output signal detected by the ACC detector 11 is charged into the capacitor 12, and the voltage across it is the AC
It is used as a gain control signal for the C amplifier 7.

According to the above operating principle, according to this embodiment, the noise superimposed on the burst signal is clipped at an appropriate level when receiving a 1-weak electric field, so the output voltage obtained by peak ACC detection is lower than that of the conventional example, which is not clipped. Therefore, the gain of the AOC amplifier 7 becomes higher than that of the conventional example, so that the degree of saturation of the reproduced output can be increased.

FIG. 7 shows a specific embodiment of the amplifier 13 and IJ tube circuit 14 portion. The amplifier 13 and the clip circuit 14f are shown separately to make it easier to understand the correspondence with the block diagram in FIG. Tori IJ
FIG. 8 shows an embodiment in which the tube circuits are integrated.

In FIG. 7, the composite force lar derehesion signal applied to terminal 21 enters the bandpass filter 6 and passes through terminal 22.
&, 22b, the color signals carried are separated. A transistor 26 (in the figure, a multi-emitter is used) constitutes a current source of the amplifier 13 that is supplied to the amplifier 13 by a differential amplifier circuit configured as shown in the figure by the carrier color signal transistors 21, 22, 26, etc. A suitable resistor 27 is connected to the emitter of the resistor 27 via an electronic switch 28 as shown. The electronic switch yf281d operates to close only for the desired time during the sampling period of the bust signal. Therefore, if the resistor 27 is selected appropriately, the current flowing through the current source transistor 26 increases only during the period when one switch 28 is closed, and therefore the current flowing through the amplifier 13. That is, transistor 21. Alternatively, the collector voltage of 22 or its differential voltage waveform becomes larger in amplitude than the color signal portion in the horizontal scanning period as the gain of the burst signal increases.

The output signal whose burst portion has been sufficiently amplified is supplied from the collector of the transistor 21.22 to the base of the transistor 30.31 forming the clip circuit 14. The clip circuit 14 is!・Ran resistors 30, 31 and 32
A differential amplifier consisting of the following is used. As is well known, if the total current flowing through the transistor 32 is Io, the collector voltage Ic of the transistor 30 or the transistor 31 is expressed as -. Here, vl and V2u are the voltages between the bases of transistor 30 and l transistor 31, respectively, and the ground, and q/kT is kT/q! at room temperature. −==
It is a constant that becomes 2 e mV. As is well known, if the collector current f Ic+ of the transistor 30 is defined as the differential input voltage between the bases of the transistors 30 and 31 (v+ - V2), then the approximate result is shown in FIG. 9.0 It is clear from FIG. By appropriately selecting the total current IOf, the amplitude can be increased above a certain differential input level.In the present embodiment shown in FIG.・-Total current An example of the characteristics is shown entirely by broken lines.

FIG. 8 shows the amplitude limiting characteristics of this differential amplifier at the amplifier 13.
This is an example in which it is used in conjunction with the clip circuit 14.

In FIG. 8, a composite color television signal applied to one terminal 21 passes through a bandpass filter 6.

A carrier color signal is output to the terminal 5o. The carrier color signal coming in at terminal 60 is double balanced as shown, combining a differential amplifier of transistors 33, 34 and 37 and a differential amplifier of transistors 35, 36 and 38. In such a configuration, a pulse is applied to the base of the transistor 370 by the vanoss supplied from one terminal 51 so that the transistor 3Y becomes conductive only during the burst period.
The base of the transistor 38 is connected to the carrier color signal period + 1 - transistor 3 during the horizontal scanning period other than the burst signal period.
A pulse is applied so that 8 becomes conductive.

That is, the carrier color signal component during one horizontal scanning period is amplified by a differential amplifier composed of one transistor 36, 36, and 38 because one transistor 38 is conducting and the transistor 37 is off, and the conductor 60 is passed through to the ACC amplifier. Sent to 7. On the other hand, - during the burst signal period, transistor 3
7 is conductive and one transistor 38 is cut off, so that the burst signal component is amplified by the differential amplifier formed by transistors 33, 34 and 37. As a result, the gain of the color signal component during the horizontal scanning period is proportional to the ratio of resistor 42/resistor 46, and the gain of the burst signal component is proportional to the ratio of resistor 42/resistor 44, so resistor 43 and resistor 44 are 46 and resistor 46, the burst portion can be made sufficiently larger than the color signal component in the horizontal scanning period, as shown in waveform B in FIG.

Therefore, if the 1-tal current of the transistor 39 and the input level supplied to the terminal 60VC are appropriately selected so as to clip the noise level as described above by the amplitude limiting effect of the differential amplifier shown in FIG. 111 o'clock S/N
The bad signal of the burst part is filtered out by the noise of the burst part and is supplied to the ACC amplifier 7 through the conductor 60.

Effects of the Invention and More - As described in detail, according to the present invention, when fully demodulating and reproducing a color television signal with a weak electric field strength, the peak A
By adopting ACC control using CC detection, the color noise becomes lighter compared to ACC control obtained using synchronous detection, and the color saturation of the image becomes too low as with conventional peak ACC detection. It has the effect of suppressing the noise and contributes to improving the color image quality when receiving a weak electric field.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a conventional color signal processing circuit - Fig. 2 is a characteristic diagram showing an example of the characteristics of the burst signal level and noise superimposed on it with respect to input electric field strength - Fig. 3 is an ACC amplifier with respect to input electric field strength Figure 4 is a waveform diagram explaining the ACC detection characteristics - Figure 6 is a system diagram of the color signal processing circuit in an embodiment of the present invention, Figure 6 is its noise filter. IJ, a waveform diagram for explaining the operation of the amplifier circuit, FIGS. 7 and 8 are specific circuit diagrams of the same embodiment, and FIG. 9 is a differential input diagram for explaining the amplitude limiting effect of the differential amplifier. It is a characteristic diagram of output voltage ratio. 6...bandpass filter, 7...ACC amplifier, 8...RY demodulator-9...B-Y
Demodulator-10... Burst gate circuit, 11.
... ACc detector, 12 ... Capacitor, 13 Moe ... Amplifier, 14 ... Clip circuit. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure JL - Kate Puffless Figure 2 Weak - Strong electric field Kazushige Figure 3 J Rinse strength - Ball Figure 4 (A) (B) Figure 5 Figure 3

Claims (3)

[Claims] (1) A bandpass filter for extracting a carrier color signal from a color telephony signal, a bandpass amplification circuit for bandpass amplifying the carrier color signal, and a detection means for detecting the burst signal amplitude. The amplification gain of the band amplification circuit is controlled by the control signal obtained by the bandpass filter, and the noise superimposed on the burst signal period of the output signal obtained by the bandpass filter is clipped at a certain level. A color signal processing circuit characterized by supplying a signal to a band amplification circuit. (2) Connected to a bandpass filter and js with 6 burst signal periods
The color signal according to claim 1, wherein the filter output signal is passed through an amplifier circuit having means for making the amplification gain larger than the amplification gain of the horizontal constant blue period, and then clipping means for limiting the amplitude is applied. Processing/Circuit. (3) The color signal processing circuit according to claim 1, wherein the IJ cup means is capable of variably adjusting the IJ cup level.