JPH01170188A - Automatic chrominance signal control circuit - Google Patents

Abstract

PURPOSE:To cause a convergent speed to be fixed regardless of a burst signal level by detecting the burst signal level in an input chrominance signal, removing noise components and multiplying a signal in which a reference signal is divided and the input chrominance signal by means of the output. CONSTITUTION:A chrominance signal Cn supplied to an input terminal 20 is multiplied with a gain Gn by a multiplier 21, thereafter, the signal is extracted from an output terminal 22, and on the other hand, a burst signal level Bn contained in the chrominance signal Cn is detected by a burst detecting circuit 23. The burt signal level Bn is multiplied with (1-K) by a coefficient multiplier 24 and thereafter, supplied to an adder 25. The adder 25 adds the output signal of the coefficient multiplier 24 and a signal in which the output signal of a latch circuit 26 is multiplied with a coefficient K by a coefficient multiplier 27, and the added result is latched by the latch circuit 26. A burst signal level Xn to be obtained is supplied to a dividing circuit 28, divided by a reference level R and thereafter, supplied to the multiplier 21, and thereby, a control is executed so that the burst signal level Bn in the chrominance signal Cn can be made to always coincide with the reference level R.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to improvements in automatic color signal control (ACC) circuits used in, for example, color television receivers.

(Prior Art) As is well known, with the recent development of digital signal processing technology, digital television receivers are being actively developed, and automatic color signal control circuits are also being digitized. This automatic color signal control circuit absorbs differences in color saturation caused by channels with different transmission characteristics and automatically adjusts the saturation so that each channel has the same saturation.

FIG. 3 shows a conventional automatic color signal control circuit which has undergone such digitization. In other words, 1 in the figure
Reference numeral 1 denotes an input terminal to which a color signal Cn separated from the composite television signal is supplied.

The color signal Cn supplied to this input terminal 11 is transmitted to the multiplier 1
After being multiplied by a gain Gn, which will be described later, by 2, the signal is output from the output terminal 13.

Furthermore, the color signals Gn and Cn output from the multiplier 12 are as follows:
The color signal Gn Cn is supplied to the burst detection circuit 14.
The burst signal level Gn Bn contained therein is detected. This burst signal level Ql Bn is determined by the subtracter 15
is subtracted from the reference level R supplied to the setting terminal 1B, multiplied by a coefficient K in the coefficient multiplier 17, and then supplied to the adder 18.

This adder 18 adds the output signal of the latch circuit 19 and the output signal of one coefficient unit, and causes the latch circuit 18 to latch the result.
The color signal Cn is supplied to the multiplier 12 as
Control is performed so that the burst signal level Bn in the middle is always made to match the reference level R.

Here, if the above operation is expressed in the form of a difference equation, Q1+1-Qn+K (R-Gn Bn)-(1-K
Bn ) On +KR...(1). Therefore, the condition for the burst signal level Bn to converge to match the reference level R is 11-KBn l <1''12) Here, if the burst signal level Bn is a constant value Bo , from the above formula (2), 11-KBo I
< 1 - (3).

Also, from the above equation (3), the burst signal level B.

When 0 < Bo < 1/K - (4), it converges in a --like manner, and when Bo = 1/K ... (5), it converges in one sampling clock, and 1 / K
< B o < 2 / K − (6)
At this time, the value of the gain Gn alternately takes positive and negative values and converges while oscillating.

That is, in the conventional automatic color signal control circuit, the color signal Cn
The convergence speed depends on the magnitude of the burst signal level BO. For example, burst signal level Bo
When satisfies the above equation (4), as shown in Fig. 4, the lower the burst signal level Bo, the faster the convergence speed and the larger the gain Gn, and the higher the burst signal level Bo, the slower the convergence and the larger the gain Gn. Gn becomes smaller.

Therefore, when the burst signal level Bo becomes low due to a weak electric field, although it converges quickly, the noise component is also input to the burst detection circuit 14, so the noise component is superimposed on the gain Gn.

In this case, since the gain On is a large value, the output of the multiplier 12 will be affected by noise even if the noise component is at a low level, and furthermore, the gain Gn will be As a result, the output of the multiplier 12 will be greatly influenced by noise.

Here, in order to keep the gain Gn at a constant value so that the output of the multiplier 12 is not affected by noise, it is necessary to set the coefficient s and the coefficient K of the coefficient 17 sufficiently small. However,
If the coefficient K is made small, there will be an inconvenience that the convergence will be delayed when the burst signal level Bo becomes high.

(Problems to be Solved by the Invention) As described above, in the conventional automatic color signal control circuit, when the burst signal level BO is low, the gain On increases, so the noise component is also multiplied at the same time. Since the multiplication output is fed back and used for further multiplication, there is a problem that it becomes unstable with respect to noise. Especially when the burst signal level Bo is low,
The above problem is made even more serious by the fact that the noise level is often high due to the weak electric field.

Therefore, the present invention has been made in consideration of the above circumstances, and provides an extremely good automatic color signal control circuit in which the convergence speed does not change depending on the magnitude of the burst signal level even though it is not affected by noise. The purpose is to provide

[Structure of the Invention] (Means for Solving the Problems) That is, the automatic color signal control circuit according to the present invention detects the burst signal level from an input color signal, removes noise components, and uses the output as a reference signal. It is configured to multiply the input color signal by the signal obtained by dividing the level.

(Function) According to the above configuration, the reference level is divided by the burst signal level from which the noise component has been removed to generate the gain On, and the gain is multiplied by the input color signal. Since the component is not fed back, it is less susceptible to noise, and the convergence speed can be kept constant regardless of the magnitude of the burst signal level.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, 2o is an input terminal to which a color signal Cn separated from the composite television signal is supplied. The color signal Cn supplied to this input terminal 2o is
After being multiplied by a gain Gn, which will be described later, by a multiplier 21, it is taken out from an output terminal 22.

Further, the color signal Cn supplied to the input terminal 20 is supplied to a burst detection circuit 23, and the burst signal level Bn included in the color signal Cn is detected.

This burst detection circuit 23, during the burst period,
The burst signal level B is determined by synchronously adding the burst signals or by detecting the peak value of the burst signals.
n is detected. Then, the burst signal level B
After n is multiplied by a coefficient (1-K) in a coefficient unit 24, it is supplied to an adder 25.

This adder 25 adds the output signal of the coefficient multiplier 24 and the output signal of the latch circuit 2B to a signal obtained by multiplying the coefficient K by the coefficient multiplier 27, and causes the latch circuit 2B to latch the result. , the latch circuit 26 outputs a burst signal level Xn from which noise components have been removed.

Then, this burst signal level Xn is determined by the division circuit 28.
is supplied to and used for division of the reference level R,
The output of the division circuit 28 is applied to the multiplier 21 as the gain Gn.
Control is performed so that the burst signal level Bn in the color signal Cn always matches the reference level R.

Here, if the above operation is expressed in the form of a difference equation, G n -R/X n -(
7) Xn+l = KXn + (1-K) Bn
=・(8). The above equation (8) represents a cyclic noise reducer. That is, the coefficient unit 24.
The 27° adder 25 and the latch circuit 2B constitute a noise attenuator, and function to sufficiently remove noise components contained in the burst signal level Bn.

Here, the signal component is the amplitude sum and the noise component is the power phase, so the noise component has an average amplitude of 1- (1+. Therefore, by approaching the value of the coefficient to "1", the noise component Furthermore, if the burst signal level Bn is a constant value Bo, then (8
), the output Xn of the latch circuit 2B converges to Bo. Therefore, Gn-R/B.

Therefore, the burst signal level Bo of the output of the multiplier 21 is always the reference level R.

Therefore, according to the configuration of the embodiment described above, the noise component included in the burst signal level Bn is reduced by the noise canceler, and the output of the multiplier 21 is used as a signal for determining the gain Gn as in the conventional case. Since it is not fed back, the gain Gn is increased by the amplified noise component.
The burst signal level Bn is not affected and the operation can be stabilized, and the convergence speed can be kept constant without changing the magnitude of the burst signal level Bn.

Next, FIG. 2 shows details of the division circuit 2B. That is, the burst signal level B is input to the input terminal 29.
o is supplied, and a reference level R is supplied to the input terminal 3o. Of these, the burst signal level BO supplied to the input terminal 29 is passed through the sign inverting circuit 31 to the arithmetic unit 3.
is supplied to one input end of 2.

On the other hand, the reference level R supplied to the input terminal 30 is set to the selector 33. The signal is supplied to the other input terminal of the arithmetic unit 32 via the latch circuit 34 and the bit shifter 35.

Note that the output of the latch circuit 34 is supplied to the sign inversion circuit 31 for control purposes. The output of the arithmetic unit 32 is then supplied to the selector 33 and also to the shift register 3B for storing the division result (R/Bo).

This division circuit 28 subtracts the burst signal level Bo from the reference level R, and if the subtraction result is positive, it bit-shifts the bar level R and performs further subtraction. Furthermore, if the subtraction result is negative, the reference level R is bit-shifted and added to the burst signal level BO.

Then, when the subtraction result is positive, "1" is input to the shift register 3B, and when it is negative, "0" is input to the shift register 3B, the calculation is stopped at a predetermined number of bits, and the value of the shift register 3B is output as the division result. In the above division operation, the bit shifter 35 performs the bit shift, and whether the arithmetic unit 32 performs subtraction or addition is controlled by the sign inversion circuit 31. Further, the selector 33 guides the reference level R to the latch circuit 34 only when starting division, and guides the output of the arithmetic unit 32 to the latch circuit 34 at other times.

The division circuit 28 has the advantage that it can be realized with a very simple configuration because it only needs to complete its calculation within one horizontal scanning period of the television signal.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] Therefore, as detailed above, according to the present invention, it is possible to provide an extremely good automatic color signal control circuit that is less susceptible to noise and whose convergence speed does not change depending on the magnitude of the burst signal level. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an automatic color signal control circuit according to the present invention, FIG. 2 is a block diagram showing details of the main parts of the same embodiment, and FIG. 3 is a block diagram showing a conventional automatic color signal control circuit. FIG. 4 is a block diagram showing the control circuit, and a characteristic curve diagram for explaining the problems of the prior art. 11... Input terminal, 12... Multiplier, 13... Output terminal, 14... Burst detection circuit, 15... Adder, 16... Setting terminal, ■7... Coefficient unit , 18...
- Adder, 19... Latch circuit, 20... Input terminal, 21... Multiplier, 22... Output terminal, 23...
Burst detection circuit, 24... Coefficient unit, 25... Adder, 2B... Latch circuit, 27... Coefficient unit, 28...
...Division circuit, 29°30...Input terminal, 31...
Sign inversion circuit, 32... Arithmetic unit, 33... Selector, 34... Latch circuit, 35... Bit shifter, 3
6...Shift register. Applicant's agent Patent attorney Takehiko Suzue Figure 4

Claims (1)

[Claims] In an automatic color signal control circuit for making a burst signal level in an input color signal correspond to a reference level, a detection means for detecting a burst signal level in the input color signal, and a noise component removal for removing a noise component from an output signal of the detection means. an automatic color filter comprising: a dividing means for dividing the reference level by the output signal of the removing means; and a multiplying means for multiplying the output signal of the dividing means by the input color signal. Signal control circuit.