JP2554090B2 - ACC circuit - Google Patents

Description

The present invention relates to an automatic color saturation control circuit (ACC circuit) in a color television receiver.

[Prior Art] In a color television receiver, a level difference between a luminance signal and a carrier color signal fluctuates due to a change in a receiving state or the like, and a color saturation degree changes. Therefore, the carrier color signal level is
An ACC circuit is provided to control the burst signal level so that it is held at the reference value.

The conventional color television receiver is of an analog type, and the ACC circuit is also an analog circuit, which is constructed as shown in the block diagram of FIG. 5, for example. The carrier color signal is output through the saturation control amplifier 1, but only the burst signal 2a indicated by the burst flag 3 is extracted from the output signal 1a by the burst gate 2 and the amplitude value of this burst signal 2a is detected by burst amplitude detection. It is detected by the circuit 4 and smoothed by the low pass filter 5.
By stabilizing and controlling the gain of the saturation control amplifier 1,
The output level of the ACC circuit is kept constant.

[Problems to be Solved by the Invention] Recently, with the progress of digital technology, the development of digital television receivers has been advanced. When digitizing the ACC circuit, the problem is the part of the low pass filter (LPF). If the LPF input is a small-amplitude signal when the ACC state is stable, and a large-amplitude signal when the ACC state changes, such as when changing channels, the analog LPF Since the dynamic range is wide, the latter can respond quickly when the ACC state changes. That is, both stabilization of the ACC operation and quick response to the change in the ACC state can be realized.

On the other hand, when the LPF is configured with a digital circuit, the ACC operation is stabilized (there is no sudden change in the ACC state due to channel change, etc.) because of the limitation of the dynamic range.
Therefore, if the response to the digital signal step is made fine and the time constant is designed to be large, there is a conflicting problem that the response becomes significantly slower when the ACC state suddenly changes.

In addition, in JP-A-60-10892 "Digital ACC circuit",
ACC circuit that forms a non-linear feedback loop by outputting the error calculation circuit that outputs the ACC control deviation by multiplying it by a constant if it is within a certain range, and by adding a constant value and outputting it if it exceeds the range. Is disclosed. However, this is a nonlinear low-pass digital filter composed of an error processing circuit and a loop filter, and has the input / output characteristics of the error processing circuit of a stable region centered at the input zero and an unstable region outside the stable region. It is only for switching between two areas. Therefore, by making the gain in the non-stable region and the gain in the stable region different, it is possible to change the repetition period of the horizontal stripe color noise to make it inconspicuous, but this is just for stabilizing the color reproduction in the steady state. This is not an effect, and does not meet the problem of how to quickly bring the control deviation into the stable region during the transitional period when the burst level of the carrier color signal suddenly changes, such as when switching channels. As long as it is not configured to switch the gain in stages, it has a problem that it takes time to stabilize.

The object of the present invention is to improve the response speed to transient fluctuations.
It is to provide the ACC circuit.

[Means for Solving the Problems] An ACC circuit of the present invention is a saturation control amplifier with variable amplification for amplifying a digital carrier chrominance signal, and a burst amplitude detection circuit for detecting a burst amplitude extracted from the saturation control amplifier. A comparator for generating a difference signal by comparing the burst amplitude detected by the burst amplitude detection circuit with a reference value, and low-pass filtering the difference signal generated by the comparator,
An AC including a low-pass filter that feeds back to the saturation control amplifier as an amplification control signal and controls the burst amplitude to a constant value.
In the C circuit, the low-pass filter has an amplitude ratio of an amplifier control signal output with respect to the differential signal input, a stable region where the absolute value of the differential signal is zero, and an absolute value of the differential signal is outside the stable region. It is characterized by comprising a non-linear low-pass digital filter having at least two or more non-stable regions divided into two sections, which are different from each other with a step-like step, and the outer area has a larger amplitude ratio.

Furthermore, in the present invention, the non-linear low-pass digital filter is composed of a recursive filter including a delay element in a feedback loop, and the number of bits of the recursive filter is larger than the number of bits of an input signal to identify the input signal. Is used as a common input bit signal of 1 bit of the cyclic filter and the next higher bit.

[Operation] According to the present invention, the input / output amplitude ratio of the nonlinear low-pass digital filter, that is, the amplitude characteristic has a step-like characteristic having a step in at least two places, and the output slope is almost equal in each divided region. Although the same, due to the above step, the relationship between the differential signal input and the amplification degree control signal output is made non-linear,
The small amplitude difference signal included in the stable region also has the small amplitude control signal output, which contributes to the stabilization of the ACC operation, while the large amplitude difference contained in the unstable region outside the stable region. For signal input, in the region that divides the unstable region into at least two, the amplitude control signal output is set to a large amplitude with an amplitude ratio that increases with a step-like step toward the outer region, and the amplitude variation of the differential signal due to channel switching On the other hand, the system can be quickly and stably converged.

In addition, the nonlinear low-pass digital filter is not a transversal filter that tends to increase in circuit size,
A cyclic filter including a delay element in a feedback loop is used, and the number of bits of this cyclic filter is set to be larger than the number of bits of the input signal. By using a common input bit signal for the upper bits of, it can be relatively easily realized by only changing the connection of the input signal of a normal cyclic low-pass filter.

EXAMPLES Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing an embodiment of the ACC circuit of the present invention, FIG. 2 is a circuit diagram showing a configuration example of the nonlinear low-pass digital filter shown in FIG. 1, and FIG. Figure 4 shows the input / output characteristics of the digital filter.
It is a circuit diagram which shows an example of a normal low-pass digital filter.

The circuit elements of the ACC circuit shown in FIG. 1 are all digital circuits, and the carrier color signal supplied as the input signal 10 is also a digital signal.

The input signal 10 is gain-controlled through a saturation control amplifier 11 to be an output color signal 10 '. The output color signal 10 'is fed back to the saturation control amplifier 11 via a feedback loop so as to have a reference burst signal level. First, the burst signal is extracted by the burst gate 12 which opens the gate during the period indicated by the burst flag 13. The extracted burst signal is averaged in amplitude of several burst signals in the subsequent burst amplitude detection circuit 14 and sent to the comparator 16 as the burst amplitude. The comparator 16 takes the difference between this burst amplitude and the preset reference value 15 and outputs it as a difference signal 16a representing the control deviation. This difference signal 1
6a is supplied to the nonlinear low-pass digital filter 17, where it is low-pass filtered by a digital signal circuit and fed back to the saturation control amplifier 11 as an amplification degree control signal 17a.

In the ACC circuit, when the ACC state is stable, the difference between the output value 14a of the burst amplitude detection circuit 14 and the reference value 15 is small, and the difference signal 16a that is the input of the nonlinear low-pass digital filter 17 is small. When the ACC status changes, the differential signal 16a
Grows. The nonlinear low-pass digital filter 17, as shown in FIG.
When 16a is small, the gain is small, and as the difference signal 16a increases, the gain increases stepwise. The characteristic shown by the dotted line in FIG. 3 is the characteristic of a normal cyclic LPF,
When the difference signal 16a is small, the absolute value [3
1] It is in the stable region below.

Next, a specific configuration of the nonlinear low pass digital filter 17 will be described with reference to FIG. It should be noted that FIG. 4 shows the configuration of a normal cyclic low-pass digital filter. To show that the nonlinear low-pass digital filter 17 can be easily realized by simply changing the connection of the normal cyclic low-pass digital filter. It is an example.

In FIG. 2, the input signal 20 of the nonlinear low-pass digital filter 17 is an 8-bit 2'S complement code signal. D7 is a sign bit. The main part 30 of the nonlinear low-pass digital filter 17 is a cyclic type including a unit delay element, is composed of 13 units, and is devised to give a nonlinear characteristic by connecting each bit of the input signal 20. ing. The limiter 40 performs an operation of limiting the amplitude to the maximum positive and negative values and outputting the maximum value. Output signal
50 is output as an 8-bit 2'S complement code signal, but in the relationship of the main part 30, the input signal 20
The bit relationship is shifted so that the output signal 50 becomes 1/2 ⁴ . Of the main part 30, the lower 5 units are of the regular patrol type. Bit inputs D0 to D4 in the form of input signal 20 are input to adders 30 (0) to 30 (4), respectively, through unit delay elements 31 (0) to 31 (4), and then adder
Return to 30 (0) to 30 (4) and signal 32 (0) to 32 (4)
Is added again to the original signal, and cyclic addition processing is performed. The adders 30 (0) to 30 (4) add and carry carry bit signals. If the main part 30 is equivalent to the lower 5 units in all units, that is, in the normal cyclic low-pass digital filter shown in FIG. 4, the number of clocks of the delay element (for example, D-type flip-flop) is At 16 (= 2 ⁴ ) clocks, the output value appears to be the same as the input value.

However, the nonlinear low-pass digital filter shown in FIG.
Reference numeral 17 is configured such that upper bits of bit input D5 and above are commonly input to two adjacent adders. For example, the bit input D5 is the adder 31 (5), the adder 31
Input both in (6). Therefore, when D5 is 1, 2 ⁶
(In the following, the decimal notation of 10 will be displayed in []) will be added separately. Note that the numbers shown in brackets [] are in units of signal values corresponding to LSB.
That is, the bits related to the output of the nonlinear LPF are S0 to S12.
Therefore, not the bit inputs D0 to D7 but D5 as S5 and S6 bits, and D6 as S7 and S8 bits are related to the output, which results in a non-linear characteristic. FIG. 3 shows the input / output characteristics of the nonlinear low-pass digital filter 17.
Since the output value changes every clock, the scale is not shown in the figure to show the tendency. Bit inputs D6 to D5 are 0, and bit inputs are represented by D0 to D4. 1/16 linearly for input signals ([0] to [31])
The output value becomes the same as the input value at 16 clocks. Next, for the input signal ([32] to [63]) where the bit input D5 is displayed as 1, the bit input D5 is S6.
Since it will be added to, it will be added only by [64]. Therefore, in the input signal [32], only [64] jumps to [96], but the output is multiplied by 1/16 and the output becomes [96] at 16 clocks. Similarly, the input is (00100000)
That is, the jap is performed at [64], and also at (00110000), that is, [96].

Thus, the nonlinear low-pass digital filter 17 divides the amplification ratio of the amplifier control signal output with respect to the differential signal input into a stable region where the absolute value of the differential signal is zero and a differential signal absolute value outside the stable region. The two non-stable regions can be made different from each other with a step-like step, and the amplitude ratio can be increased in the outer regions.

It should be noted that the above-mentioned input / output characteristics are symmetrical with respect to the signal of the negative polarity when the 2'S complement code signal is input, with respect to the signal of the positive polarity. When S12 and S11 become 01 or 10, the positive or negative polarity signal overflows.
1 '= 0, others are set to "1", and when negative, S11' = 1, others are set to "0", and the amplitude is limited to the maximum positive and negative values.

Hereinafter, the ACC operation of FIG. 1 will be described in consideration of the input / output characteristics of the nonlinear low-pass digital filter 17. In the state where ACC is stable, the burst signal level 14a included in the output of the saturation control amplifier 11 substantially matches the reference value 15, so that the output of the comparator 16 becomes small and the nonlinear low-pass digital filter 17 Input is between [-32] and [+31]. Therefore, the circuit operates in the same manner as a normal linear low-pass digital filter and stabilizes the circuit. Next, when the input digital carrier color signal changes due to channel switching or the like, a considerable amplitude difference occurs between the output of the saturation control amplifier 11 and the reference burst signal. Generally, the ACC circuit has to deal with a signal of about +6 dB to -20 dB as an input signal, so that the output differential signal of the comparator 16 becomes considerably large. As a result, the input to the nonlinear low-pass digital filter 17 greatly exceeds [32] that defines the boundary of the stable region, and the amplitude ratio of the amplification control signal to the differential signal input increases nonlinearly in the unstable region. .

In the non-stable region, the gain changes with a stair-like step at two points of [64] and [96] in the absolute value of the difference signal, so that stronger feedback is applied as the control deviation, that is, the difference signal input is larger. Has become. Therefore, unlike a normal linear low-pass digital filter that feeds back with a simple gain, the same effect as increasing the gain of the feedback loop is obtained as the control deviation is larger, and the ACC operation is pulled in immediately after channel switching, that is, the control deviation. It is possible to complete the driving into the stable region in a short time.

In the above embodiment, the input / output characteristics of the nonlinear low-pass digital filter are configured so that the gain is switched in two stages in the unstable region.
It is also possible to switch the gain with a step difference of more than one step.

Further, in the embodiment, the nonlinear low-pass digital filter 17
Although it is configured to output the amplification control signal by using, a low-pass filter characteristic is provided by a normal recursive filter, a ROM is arranged on the input side, and a non-linear relationship is provided in the input / output characteristic of the ROM. Good. However, if ROM is used, there is a drawback in that the circuit as a whole becomes complicated, and the merit of the nonlinear low-pass digital filter that can realize the conventional linear low-pass digital filter by simple wiring change is lost. I won't.

As described above, according to the ACC circuit of the present invention, the low-pass filter that low-pass filters the differential signal with respect to the reference value of the burst amplitude extracted from the digital carrier color signal and feeds it back to the saturation control amplifier. The amplitude ratio of the output to the differential signal input, a stable region where the absolute value of the differential signal is centered at zero,
A non-linear low-pass digital filter in which the absolute value of the difference signal is different from at least two or more unstable regions divided outside the stable region with a step difference, and the amplitude ratio is increased toward the outer region is used. According to the amplitude division of the differential input signal, the output can have a stepwise amplitude step in at least three division areas, and even if the output slopes in each division area are substantially the same. , The amplitude ratio of the output signal to the input signal changes stepwise due to the above-mentioned amplitude step, so that the amplification control signal output is also set to the small amplitude for the small amplitude difference signal input included in the stable region. On the one hand, it contributes to the stabilization of the operation, and on the other hand, for a large-amplitude differential signal input included in the non-stable region outside the stable region, the outside of the non-stable region is divided into By setting the amplitude control signal output to a large amplitude with an amplitude ratio that increases as the region increases in steps, the same effect as increasing the gain of the feedback loop as the control deviation increases can be obtained. It is possible to complete the pull-in of the ACC operation, that is, the driving of the control deviation into the stable region in a short time, and it is possible to achieve a high-speed and stable ACC operation.

Further, the present invention provides a nonlinear low-pass digital filter,
The cyclic filter includes a delay element in a feedback loop, the number of bits of the cyclic filter is larger than the number of bits of the input signal, and a specific higher-order bit signal of the input signal Since the common input bit signal of the higher order bits is used, a normal recursive filter that includes a delay element in the feedback loop is used without using a transversal filter that enlarges the circuit scale. By making the number of bits of the filter larger than the number of bits of the input signal and connecting so that a specific higher-order signal of the input signal becomes a common input bit signal of the 1-bit of the recursive filter and the next higher-order bit, In addition, the desired non-linear characteristic can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the ACC circuit of the present invention, FIG. 2 is a circuit diagram showing a configuration example of the nonlinear low-pass digital filter shown in FIG. 1, and FIG. FIG. 4 is a circuit diagram showing an example of a normal low-pass digital filter, and FIG. 5 is a circuit block diagram showing an example of an analog type ACC circuit. 10 …… Carrier color signal 10 ′ …… Output color signal 11 …… Saturation control amplifier 12 …… Burst gate 13 …… Burst flag 14 …… Burst amplitude detection circuit 15 …… Reference value 16 …… Comparator 17 …… Non-linear Low-pass digital filter 20 Input signal 30 Main part 30 (1) Adder 31 (1) Unit delay element 32 (1) Return signal 40 Limiter 50 Output signal

Claims (2)

(57) [Claims] 1. A saturation control amplifier having a variable amplification degree for amplifying a digital carrier color signal, a burst amplitude detection circuit for detecting a burst amplitude extracted from the saturation control amplifier, and a burst detected by the burst amplitude detection circuit. A comparator that compares the amplitude with a reference value and generates a difference signal, and the difference signal generated by the comparator is low-pass filtered and fed back to the saturation control amplifier as an amplification degree control signal to control the burst amplitude to a constant value. In the ACC circuit including a low pass filter, the low pass filter has an amplitude ratio of an amplifier control signal output with respect to the differential signal input, a stable region where the absolute value of the differential signal is zero, and the differential signal. At least two or more unstable regions whose absolute values are divided outside the stable region are made different from each other with a step-like step, and the amplitude ratio is increased toward the outer region. ACC circuit, comprising the non-linear low-pass digital filter. 2. The non-linear low-pass digital filter is composed of a recursive filter including a delay element in a feedback loop,
The number of bits of the cyclic filter is larger than the number of bits of the input signal, and a specific upper bit signal of the input signal is a common input bit signal of 1 bit of the cyclic filter and the next higher bit. The ACC circuit according to claim 1, wherein: