JPH03258118A - Gain control circuit - Google Patents

Abstract

PURPOSE:To stably and surely correct the vibratory fluctuation of an input signal by reducing a feedback gain in response to a noisy state. CONSTITUTION:When the S/N of a video signal SV is deteriorated, even when the result of comparison of a comparator circuit 12 changes from '0' level in a small range, the signal level of a control signal SCONT fed back to a variable gain amplifier circuit 3 is kept to '0' level, the result of comparison of the circuit 12 rises largely, then the signal level of the signal SCONT rises. Thus, even when an erroneous result is obtained by a reference level detection circuit 10 due to noise, the gain of the circuit 3 is controlled with less feedback quantity by the noise and the amplitude change in a digital video signal DV due to the noise is effectively evaded by a noise detection circuit 22 and an amplifier circuit 24, then the vibratory fluctuation of the input signal is corrected stably and surely.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Overview of the invention C. Conventional technology (Figs. 12 to 14) D. Issue B to be solved by the invention (Fig. 12 to 14) 8. Figure 1) 1 action (Figure 1) G embodiment (Figures 1 to 11) (G1> First embodiment (Figures 1 and 2) (G2) Second embodiment (Figure 1) 3 to 5) (G3) Third embodiment (
Figures 6 to 8) (G4) Other embodiments (Figures 9 to 11)
Figure) H Effect of the Invention A Field of Industrial Application The present invention relates to a gain control circuit, and can be applied to, for example, video equipment that converts a video signal into a digital signal and processes it.

B. Summary of the Invention The present invention enables stable and reliable gain control by reducing feedback gain in a gain control circuit according to noise conditions.

C. Prior Art Conventionally, in video equipment that converts video signals into digital signals and processes them, fluctuations in the signal level of the video signals are corrected, for example, by gamma correction and non-linear emphasis processing. .

That is, as shown in FIGS. 12 and 13, in the signal processing circuit 2, the human signal is subjected to non-linear emphasis processing, which is non-linear processing, and the white level of the input signal is set to 255/255.
256, human power level 0/256 to 127/25
6 range is gain 2, input level 128/256~25
The range of 5/256 is amplified with a gain of 1/2.

In such nonlinear processing, the amplitude of the input signal is
/4, and the white level of the input signal changes to 374.
If the signal level changes to , it becomes impossible to process the human signal with the correct characteristics.

For this reason, the gain control circuit 1 is used to correct signal level fluctuations of the video signal and maintain the digital video signal Dv at a predetermined signal level.

That is, in the gain control circuit 1, the video signal Sv is amplified by the variable gain amplifier circuit 3 and then output to the clamp circuit 4.

The clamp circuit 4 clamps the black level of the video signal Sv to a predetermined signal level based on a predetermined clamp pulse, thereby correcting DC level fluctuations of the video signal Sv, and outputs the corrected signal to the analog-to-digital conversion circuit 6. .

Thereby, the video signal Sv is converted into a digital signal via the analog-to-digital conversion circuit 6, and the digital video signal Dv is output to the signal processing circuit 2.

At this time, the reference level detection circuit 10 detects the signal level of the digital video signal Dv using a predetermined reference pulse P1 as a reference, thereby detecting the signal level of the reference signal inserted in the vertical blanking period of the digital video signal Dv. The level is detected and the detection result is output to the comparison circuit 12.

As a result, a predetermined comparison reference value D is determined via the comparison circuit 12.
A comparison result with 0F is obtained, and the comparison result is output to the amplifier circuit 14.

As shown in FIG. 14, the amplifier circuit 14 is composed of an inverting amplifier circuit that outputs an output signal at a signal level proportional to the signal level of the human input signal, and converts the output signal of the amplifier circuit 14 into a digital-to-analog conversion circuit (D /A) 16 and is output to the variable gain amplifier circuit 3 via a low-pass filter circuit (LPF) 18.

Thereby, in the variable gain amplifier circuit 3, feedback control is performed so that the comparison reference value DoF and the signal level of the reference signal match, and amplitude fluctuations of the video signal Sv can be corrected.

As a result, even if the DC level and amplitude fluctuate, the fluctuations can be corrected via the gain control circuit 1.

Problem II to be solved by the invention D By the way, in this type of video equipment, a video signal Sv with a poor SN ratio may be input.

In this case, the reference level detection circuit 10 may detect a fair signal level with noise mixed in the video signal Sv, and the gain control circuit 1 will accordingly correct the amplitude incorrectly.

That is, in the conventional gain control circuit 1, when the video signal 5vO3N ratio deteriorates, there is a problem that the feedback gain cannot be controlled stably and reliably, and the amplitude of the digital video signal Dv changes accordingly due to noise. .

The present invention has been made in consideration of the above points, and aims to propose a gain control circuit that can stably and reliably control the gain even with an input signal having a poor S/N ratio.

8 Means for Solving the Problems In order to solve the problems, the present invention includes an amplifier circuit 3 that amplifies the input signal Sv, an analog-digital conversion circuit 6 that converts the output signal of the amplifier circuit 3 into a digital signal Dv, The gain of the amplifier circuit 3 is determined based on the detection results of the signal level detection circuit IO that detects the signal level of the digital signal Dv, the noise state detection circuit 22 that detects the noise state of the input signal Sv, and the signal level detection circuit 10. In addition to feedback control, based on the detection result of the noise state detection circuit 22,
Accordingly, feedback control circuits 12, 16, 18, and 24 are provided to reduce the gain of feedback control according to the noise state.

By reducing the gain of the feedback control according to the noise state, it is possible to stably and reliably correct signal level fluctuations of the input signal Sv and perform gain control even if the SN ratio deteriorates.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

(Gl) First Embodiment In FIG. 1, in which parts corresponding to those in FIG. Detect amount.

That is, the noise detection circuit 22 detects the noise state of the video signal Sv by extracting from the digital video signal Dv a signal component in a frequency band sufficiently lower than the horizontal scanning frequency of the digital video signal Dv and detecting the signal level. do.

The amplifier circuit 24 switches the table based on the detection result of the noise detection circuit 22, thereby switching the input/output characteristics according to the noise state.

In other words, as shown in FIG. 2, when the S/N ratio of the video signal Sv is good, the amplifier circuit 24 outputs an output signal at a signal level proportional to the signal level of the input signal. The output signal of the comparison circuit 12 is fed back to the variable gain amplifier circuit 3 with the same feedback gain as the conventional gain control circuit 1.

On the other hand, when the video signal 5vO3N ratio is poor, the amplifier circuit 24 continuously switches the characteristics as shown by arrow a as the SN ratio deteriorates.

In this case, when the input/output characteristics have changed the most, the comparator circuit 1
In the range where the output signal level of 2 is small, the gain is O,
When the output signal level increases, the output signal of the comparator circuit 12 is fed back to the variable gain amplifier circuit 3 at a gain of -1/2 and a gain of -1.

As a result, when the S/N ratio of the video signal Sv is poor, the control signal S is fed back to the variable gain amplifier circuit 3 even if the comparison result of the comparator circuit 12 varies within a minute range from the O level. H
When the signal level of T is held at O level and the comparison result of the comparator circuit 12 rises significantly, the control signal S
,. , 47 signal level.

Therefore, even if the reference level detection circuit 10 obtains an incorrect detection result due to noise when the video signal 5VO3N ratio is poor, the gain of the variable gain amplifier circuit 3 can be controlled with a feedback amount that is smaller by the amount of noise. With a simple configuration that only includes the noise detection circuit 22 and the amplifier circuit 24, changes in the amplitude of the digital video signal Dv due to noise can be effectively avoided.

Therefore, the gain can be controlled stably and reliably even in the video signal Sv outputted from a video tape recorder or video disk player, which has a poor S/N ratio compared to, for example, television broadcasting. , the video signal Sv can be processed with the correct characteristics.

Furthermore, by continuously switching the table of the amplifier circuit 24 according to the noise state, it is possible to effectively prevent the generation of noise accompanying the switching operation.

In the tank bottom described above, the detection result of the reference level detection circuit 10 is compared with a comparison reference value in the comparison circuit 12, and the comparison result is fed back to the variable gain amplifier circuit 3 via the amplifier circuit 24.

At this time, the noise detection circuit 22 detects the signal level of the noise, thereby detecting the noise state of the video signal Sv, and the feedback gain of the amplifier circuit 24 is controlled based on the detection result.

That is, when the SN ratio of the video signal Sv is good, the gain of the variable gain amplifier circuit 3 is controlled at a signal level proportional to the output signal level of the comparison circuit 12, and the amplitude change of the video signal Sv is corrected as in the conventional case.

On the other hand, if the video signal 5vO3N ratio is poor, the SN
As the ratio deteriorates, the characteristics of the amplifier circuit 24 are continuously switched, and the variable gain amplifier circuit 3 has a feedback gain that is reduced by the amount of noise.
gain is controlled.

As a result, with a simple configuration that only includes the noise detection circuit 22 and the amplifier circuit 24, it is possible to effectively avoid changes in the amplitude of the digital video signal Dv due to noise.

According to the above configuration, by switching the characteristics of the amplifier circuit 24 according to the noise condition and controlling the gain of the variable gain amplifier circuit 3 with the feedback gain according to the noise condition, the video signal due to noise can be reduced with a simple configuration. Changes in the amplitude of Sv can be effectively avoided, and gain control can be performed more stably and reliably.

(G2) Second Embodiment In FIG. 3, in which parts corresponding to those in FIG.
is output to the analog-to-digital conversion circuit 31.

As a result, the analog-to-digital conversion circuit 31 converts the control signal S, into the corresponding control signal S,. The video signal Sv is converted into a digital video signal Dv based on the signal level of the NT, and the control signal S
,. 9. The amplitude fluctuation of the video signal Sv is corrected according to the signal level of the video signal Sv.

Accordingly, as shown in FIGS. 4 and 5, the amplifier circuit 32 continuously switches its characteristics as indicated by the arrow a according to the noise state, and outputs the control signal s coNt with positive feedback characteristics.

Furthermore, in accordance with this, an amplifier circuit 33 is provided in place of the variable gain amplifier circuit 3, and the video signal Sv is amplified with a constant gain.

According to the configuration shown in FIG. 3, the analog-to-digital conversion circuit 3
1 is a control signal S. Output N7 and @control signal S at t1
(By converting the video signal Sv into a digital video signal Dv based on ON? and switching the feedback gain of the amplifier circuit 32 according to the noise condition, the same effect as the configuration shown in FIG. 1 can be obtained. .

Furthermore, at this time, by feeding back the control signal s coNt to the analog-to-digital conversion circuit 31 and correcting the amplitude fluctuation of the video signal Sv, an amplifier circuit 33 that amplifies the video signal Sv with a constant gain instead of the variable gain amplifier circuit 3 is installed. can be used, and the feedback gain can be controlled stably and reliably with a simpler configuration than the configuration shown in Part 1 of FIG.

(G3) Third Embodiment In FIG. 6, 40 indicates a gain 117111 circuit as a whole, which corrects the signal level of a video signal SVI having a control code of a predetermined format instead of the video signal Sv.

That is, as shown in FIG. 7, in the video signal SvI, the type of signal source can be identified using a predetermined control code.

In the control code, the 13th and 100th control bits are used to identify whether the signal source is satellite broadcasting (represented by the symbol BS), and the 14th control bit is used to identify whether the signal source is a video disc player. (represented by the symbol DISK) or a video tape recorder (represented by the symbol V
(represented by TR) can be identified.

Furthermore, the 15th control bit can be used to identify whether the SN ratio of the video signal Svl is good or bad.

As a result, as shown in FIG. 8, the video signal S□O3N ratio can be determined using the 13th to 15th control bits of the control code.

In other words, in satellite broadcasting, video disc players, and video tape recorders, satellite broadcasting is generally the signal source with the best signal to noise ratio, followed by video disc players and video tape recorders, in which order the signal to noise ratio deteriorates.

Therefore, in this embodiment, by controlling the feedback gain based on the control code, the video signal S□
The feedback gain is controlled according to the noise condition of the video signal S□
to compensate for signal level fluctuations.

That is, the control code discrimination circuit 42 takes in the digital video signal D Vl at a predetermined timing,
Thereby, the signal level of the video signal Sv+ is detected at a predetermined timing, and the control code CD is detected.

Furthermore, the control code discrimination circuit 42 outputs a control signal to the variable gain amplifier circuit 44, and switches the feedback gain of the variable gain amplifier circuit 44 according to the 13th to 15th control bits.

In other words, a video signal S with a good signal-to-noise ratio is obtained by receiving satellite broadcasting.
When v+ is input, the output signal of the comparator circuit 12 is amplified and fed back to the variable gain amplifier circuit 3 similarly to the conventional gain control circuit.

On the other hand, when satellite broadcasting is received and a video signal Sv+ with a poor SN ratio is input, or when a video signal S□ with a good SN ratio is input from a video disc player, when satellite broadcasting is received and the SN ratio is Video signal S Vl with good ratio
The control signal S Coal is fed back with a reduced feedback gain compared to the case where the control signal S Coal is input.

Furthermore, when a video signal SVI with a poor SN ratio is input from a video disc player, or when a video signal Svl with a good SN ratio is input from a video tape recorder, the feedback gain is further reduced; When a video signal SVI with a poor S/N ratio is input from the input signal SVI, the feedback gain is further reduced by -stage.

Thereby, the amplifier circuit 44 can reduce the feedback gain according to the noise state obtained via the control code, and can stably and reliably control the feedback gain.

According to the configuration of FIG. 6, even if the noise condition is detected based on the control code of the video signal Sv+ and the feedback gain is controlled according to the noise condition, the same effect as the configuration of FIG. 1 can be obtained. can be obtained, and amplitude fluctuations of the video signal S Vl can be corrected stably and reliably.

(G4) Other embodiments In the above-mentioned embodiments, FIGS. 2, 4 and 5
Although the case where the feedback gain is reduced with the characteristics shown in the figure has been described, the present invention is not limited to this, and the feedback gain may be reduced with the characteristics shown in FIGS. 9 to 11.

That is, in FIG. 9, the gain is reduced as a whole with respect to the output signal of the comparator circuit 12, and the 10th
In the figure, the feedback gain is reduced only when the output signal level of the comparison circuit 12 is small.

Further, in FIG. 11, a dead zone is provided around the 0 level, and the width of the dead zone is changed according to the noise condition to reduce the feedback gain.

Even in this case, the same effects as those of the above embodiment can be obtained.

Furthermore, in the above-described embodiment, the case where non-linear emphasis processing is performed in the signal processing circuit has been described, but the present invention is not limited to this, and the present invention is not limited to the case where non-linear processing such as gamma correction is performed, and furthermore, the present invention is not limited to non-linear processing. It can be widely applied when performing various signal processing.

Further, in the above-described embodiment, a case has been described in which the noise detection circuit 22 or the control code discrimination circuit 42 detects a noise state, but the present invention is not limited to this. For example, the signal level of noise is detected directly from the video signal Sv. Various detection methods can be widely applied.

Further, in the above-described embodiment, a case has been described in which the DC level and amplitude fluctuations of a video signal are corrected. First, it can be widely applied to correcting amplitude fluctuations of various human input signals.

Effects of the Invention As described above, according to the present invention, by reducing the feedback gain according to the noise condition, the feedback gain can be controlled stably and reliably with a simple configuration, thereby reducing the amplitude fluctuation of the input signal. It is possible to obtain a gain control circuit that can stably and reliably correct.

...Signal processing circuit, 3...Variable gain amplifier circuit, 6.31...Analog-digital conversion circuit,
14.24.32.44...Amplification circuit, 22.
... Noise detection circuit, 42 ... Control code discrimination circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a gain control circuit according to an embodiment of the present invention, FIG. 2 is a characteristic curve diagram showing input/output characteristics of the amplifier circuit, and FIG. 3 is a block diagram showing a second embodiment. Figures 4 and 5 are characteristic curve diagrams for explaining feedback gain switching, Figure 6 is a block diagram showing the third embodiment, and Figures 7 and 8 are route diagrams for explaining control codes. , FIGS. 9 to 11 are characteristic curve diagrams showing other embodiments, FIG. 12 is a characteristic curve diagram for explaining nonlinear processing, FIG. 13 is a block diagram showing a conventional gain control circuit, and FIG.
The figure is a characteristic curve diagram for explaining the feedback characteristic.

Claims (1)

[Claims] An amplifier circuit that amplifies an input signal; an analog-to-digital conversion circuit that converts the output signal of the amplifier circuit into a digital signal; a signal level detection circuit that detects the signal level of the digital signal; a noise state detection circuit that detects the noise state of the signal; and feedback control of the gain of the amplifier circuit based on the detection result of the signal level detection circuit; A gain control circuit comprising: a feedback control circuit that reduces the gain of the feedback control according to a state.