JP2002009620A - Video camera system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a video camera system that reduces power consumption and suppresses quantization noise, when a high gain is required. SOLUTION: An AGC circuit 3 amplifies an analog signal from a sensor 2, an analog/digital converter 4 converts the signal into a digital signal, which is amplified by an AGC circuit 5 and processed by a signal processing circuit 6. A level detection circuit 9 detects the level of an output luminance signal Y of the signal-processing circuit 6, a microcomputer 7 compares the detected value with a reference value and generates an aperture control signal of an iris 1, a gain control signal 73 of the AGC circuit 3, and a gain control signal 75 of the AGC circuit 5, depending on the comparison result. The microcomputer 7 minimizes the gain of the AGC circuits 3, 5, to make the detected value match with the detected value under the control of the aperture of the iris 1 at low illuminance, the microcomputer 7 fully opens the iris, minimizes the gain of the AGC circuit 5 and makes the detected value match with the reference value under the gain control of the AGC circuit 3 at medium illuminance, and the microcomputer 7 fully opens the iris 1, maximizes the gain of the AGC circuit 3 and makes the detected value match wit the reference value under the gain control of the AGC circuit 5 at high illuminance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control device suitable for use in a video camera device or the like.

[0002]

2. Description of the Related Art Generally, in a video camera device,
For example, the technical report of the Institute of Television Engineers of Japan Vol. 15, No. 7
(Jan, 1991) As described in pp. 37-42, digitization of signal processing has been promoted for the purpose of miniaturization and weight reduction, high functionality, low power consumption, and the like. As with the video camera device that performs analog processing, an automatic gain control circuit is provided to keep the camera output signal level constant irrespective of the output level of a sensor that converts light information from a subject into an analog electric signal.

[0003]

However, in the above-mentioned conventional video camera device, the automatic gain control circuit is provided between the sensor and the analog-digital converter, and the automatic gain control is performed by analog processing. For this reason, for example, in the case of shooting at low illuminance, the gain of the automatic gain control circuit must be sufficiently increased to obtain a constant output signal, and in order to obtain a high gain,
The scale of the automatic gain control circuit increases, and the power consumption increases in proportion to the circuit scale. This is a major problem for a video camera device aiming at low power consumption as one purpose.

[0004] At present, the reduction in power consumption of devices is approaching its limit in analog devices, while digital devices are making further progress. Therefore, in consideration of the above problems and technical trends, it is conceivable to digitize the automatic gain control circuit in order to reduce the power consumption of the video camera device. However, when all the automatic gain control circuits are digitized, there is a problem that quantization noise increases at a high gain, and the S / N of the camera output signal deteriorates.

An object of the present invention is to solve such a problem,
An object of the present invention is to provide an automatic gain control device having a good / N ratio, a small circuit scale, and low power consumption.

[0006]

In order to achieve the above object, the present invention provides a first variable gain amplifier for converting an input signal into an analog signal and amplifying the input signal with a gain according to a first control signal. Circuit, an analog-to-digital converter for converting an output signal of the first variable gain amplifier circuit into a digital signal, and the digital signal output from the analog-to-digital converter with a gain corresponding to a second control signal A second variable gain amplifying circuit, a signal processing circuit for processing an output digital signal of the second variable gain amplifying circuit, a level detection circuit for detecting a level of an output signal of the signal processing circuit, A control circuit for generating the first and second control signals for setting the gains of the first and second variable gain amplifying circuits so that the value detected by the level detection circuit becomes equal to a preset reference value. A configuration with a.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an automatic gain control device according to the present invention used in a video camera device, wherein 1 is an iris, 2 is a sensor, and 3 is a variable gain amplifier circuit (hereinafter, analog AGC) for analog processing. 4 is an A / D (analog-digital) converter, 5 is a variable gain amplifying circuit (hereinafter, referred to as a digital amplifier) for digital processing.
6 is a signal processing circuit, and 7 is a digital AGC circuit.
Is a microcomputer (hereinafter referred to as a microcomputer), 8
Is a drive circuit, and 9 is a level detection circuit.

In FIG. 1, light from a subject (not shown) is incident on a sensor 2 through an iris 1. Sensor 2
Scans a subject image generated on the light receiving surface by a control signal supplied from the drive circuit 8, generates an analog electric signal having the subject image as information content, and supplies the analog electric signal to the analog AGC circuit 3. The electric signal is amplified by the analog AGC circuit 3 with a gain according to the digital control signal 73 supplied from the microcomputer 7, and the A / D converter 4 converts the digital signal of the quantization bit number m (m is a positive integer) (Hereinafter referred to as an m-bit digital signal) 501 and supplied to the digital AGC circuit 5.

Here, a specific example of the digital AGC circuit 5 will be described with reference to FIG. Here, 51 is a gain control unit,
511 is a latch circuit, 512 is a serial-parallel converter (hereinafter, referred to as S / P converter), 513 is a latch circuit, 514 is a multiplier, 515 is a latch circuit, and 52 is a limiter.

In FIG. 1, a digital AGC circuit 5 comprises a gain control section 51 and a limiter 52.
The gain control unit 51 includes a multiplier 514, an S / P converter 512
And latches 511, 513, and 515.

M output from A / D converter 4 (FIG. 1)
The bit digital signal 501 is latched by the latch circuit 511 for each latch pulse 75b of the control signal 75 supplied from the microcomputer 7 (FIG. 1), and the latch output is supplied to the multiplier 514. Gain control signal 75a of control signal 75 supplied from microcomputer 7 (FIG. 1)
Is converted into a p (p is a positive integer) bit gain control signal by the S / P converter 512 and is latched by the latch circuit 513 for each latch pulse 75b. This latch circuit 5
The gain control signal output from 13 is multiplied by a digital signal output from latch circuit 511 by multiplier 514. The multiplier 514 outputs the higher q bits of these multiplied values, and the latch circuit 515
Is latched every latch pulse 75b. The output signal of the latch circuit 515 is supplied to the limiter 52.

The limiter 52 changes the level of the output signal of the latch circuit 515 to n according to a predetermined input / output characteristic.
(N is a positive integer less than or equal to q) bits, and the limited n-bit output signal 502 is converted to the signal processing circuit 6 of FIG.
To supply.

FIG. 3 shows an example of the input / output characteristics of the limiter 52. The level of the output signal is limited to (2 ⁿ -1) above the level of (2 ⁿ -1 -x). are doing. Here, x is an arbitrary integer.

Returning to FIG. 1, in the signal processing circuit 6, the above-mentioned technical report of the Institute of Television Engineers of Japan, Vol. 15, No. 7 (Ja
n, 1991) Similarly to the signal processing circuits described in pp. 37 to 42, an n-bit output digital signal 502 of the digital AGC circuit 5 is supplied, and 2 or 3
A luminance signal Y and a chrominance signal C are generated using digital signals 502 for one line (where one line is one horizontal scanning period). The luminance signal Y and the color signal C are supplied to a next-stage processing circuit (not shown) to generate a color video signal.
The luminance signal Y is also supplied to the level detection circuit 9, which detects the level of the luminance signal Y in a predetermined area in the image display screen, and supplies the obtained detection value to the microcomputer 7.

The microcomputer 7 compares the detection value from the level detection circuit 9 with a reference value set in the microcomputer 7 in advance to determine the illuminance of the subject, and an aperture control signal 71 corresponding to the illuminance. And the gain control signals 73 and 75, respectively, so that the iris 1 and the analog A
It is supplied to the GC circuits 3 and 5. The control operation of the microcomputer 7 will be described more specifically with reference to FIGS.

As shown in FIG. 4, the microcomputer 7 divides the illuminance of the object into areas 1, 2, 3 and a reference value indicating a boundary of each area and a detection value of the level detection circuit 9 (FIG. 1). To determine which of the regions 1, 2, and 3 the subject illuminance falls in, and according to the determination result, the iris 1 and the analog A are adjusted so that the reference value and the detected value match.
It controls the GC circuit 3 and the digital AGC 5.

When the illuminance is within the range 1, the respective control signals 7 are controlled so that the gains of the AGC circuits 3 and 5 become minimum.
After setting 3,75, an aperture control signal 71 for adjusting the incident light amount of the sensor 2 by the aperture amount of the iris 1 is generated so that the output signal of the camera becomes constant. Thereby, the light amount of the incident light of the sensor 2 is adjusted so that the above-mentioned detection value matches the above-mentioned reference value. When the illuminance is within the area 2, the microcomputer 7 sends the aperture control signal 71 so that the iris 1 is fully opened and the digital AGC circuit 5
After the gain control signal 75 is set so as to minimize the gain, the gain control signal 73 is generated so that the signal level is adjusted by the analog AGC circuit 3. That is,
The gain of the analog AGC circuit 3 is controlled by the gain control signal 73 so that the detected value matches the reference value. Further, when the illuminance is within the area 3,
The aperture control signal 71 is set so that the iris 1 is fully opened, and the gain control signal 73 is set so that the gain of the analog AGC circuit 3 is maximized.
The gain control signal 75 is generated so that the signal level is adjusted by the circuit 5. That is, the gain of the digital AGC circuit 5 is controlled by the gain control signal 75 so that the detected value matches the reference value.

The above series of operations constitute a feedback loop, whereby the output signal of the camera is always kept constant.

The operation of the microcomputer 7 will be described in more detail with reference to FIG. 5. First, the gains of the analog AGC circuit 3 and the digital AGC circuit 5 shown in FIG. (Step S2), it is determined whether or not the level of the luminance signal Y matches the reference value. This determination is made in steps S3 and S10. If they match, the aperture of the iris 1, the analog AGC circuit 3 and the digital AGC circuit 5
Are maintained as they are, and the gains of steps S3 and S1 are maintained.
The operation of the loop of 0, S2 is repeated. Analog AG
The initial setting values of the gains of the C circuit 3 and the digital AGC circuit 5 are the minimum values of the above-mentioned gains.

When the level of the luminance signal is smaller than the reference value (step S3), it is determined whether or not the iris 1 is fully opened (step S4). Until the iris 1 is fully opened, steps S7, S16, S17, S2, S3, and S3 are performed. A series of operations in S4 is repeated. Of course, if the level of the luminance signal coincides with the reference value during this time, the operation is stopped, and the process proceeds to the series of operations in steps S2, S3, and S10 described above. That is, in this operation, it is determined whether or not the illuminance of the subject is in the area 1 in FIG. 4. If the illuminance is in this area 1, the level of the luminance signal is determined based on the aperture of the iris 1. Try to match the value.

When the luminance signal level does not match the reference value even when the iris 1 is fully opened (steps S3 and S3).
4) It is determined whether or not the gain of the analog AGC circuit 3 is the maximum (step S5).
A control signal 73 for increasing the gain of the C circuit 3 is generated (step S8), and sent to the analog AGC circuit 3 during the blanking period to increase the gain (step S16,
17). This operation is performed in steps S8, S16, S
A series of operations of 17, S2, S3, S4, and S5 is repeated until the level of the luminance signal matches the reference value or the gain of the analog AGC circuit 3 becomes maximum. If the level of the luminance signal coincides with the reference value during this time, the operation is stopped, and the process proceeds to the series of operations in steps S2, S3, and S10 described above. That is, in this operation, the illuminance of the subject is
It is determined whether or not it is in the area 2 in
If it is in this area 2, the level of the luminance signal is made to match the reference value by the gain control of the analog AGC circuit 3.

If the level of the luminance signal does not match the reference value even if the gain of the analog AGC circuit 3 is maximized (step S5), then steps S6, S9 and S1 are performed.
The control signal 75 is sent to the digital AGC circuit 5 during the blanking period so that the series of operations of S6, S17, S2 to S5 is repeated, and the gain of the digital AGC circuit 5 is maximized. Of course, if the level of the luminance signal coincides with the reference value during this time, the operation is stopped and the above steps S2 and S2 are performed.
Move to a series of operations in S3 and S10. That is, the operation is
It is determined whether or not the subject illuminance is in the area 3 in FIG.
By controlling the gain of the GC circuit 5, the level of the luminance signal is made to coincide with the reference value.

The above is the operation at the start of the operation such as after the power is turned on. However, when the level of the luminance signal becomes lower than the reference value due to a change in the subject or a change in the image pickup scene during the operation. This is determined in steps S3 and S4, and as a result of this determination, the microcomputer 7 performs the following control operation.

(1) When the illuminance of the subject changes from region 1 to region 3 in FIG. 4; as described above, in region 1, the gains of analog AGC circuit 3 and digital AGC circuit 5 are the minimum values, and iris 1 Is between a fully open state and a minimum open state. In this case, it is the same as the case where the illuminance of the subject is in the area 3. First, when it is determined that the level of the luminance signal is smaller than the reference value (step S <b> 3), the iris 1 is not fully opened. Therefore (step S4), as described above, the operation of the loop including step S7 is performed, the aperture control signal 71 is generated, the iris 1 is fully opened, and thereafter, the operation of the loop including step S8 is performed, and the gain control is performed. The signal 73 is generated to set the gain of the analog AGC circuit 3 to the maximum value. When the gain of the analog AGC circuit 3 reaches the maximum value, the operation of the loop including step S9 is performed to generate the gain control signal 75 to control the gain of the digital AGC circuit 5, thereby obtaining the level of the luminance signal. Becomes equal to the reference value.

(2) When the illuminance of the subject changes from region 1 to region 2 in FIG. 4; first, when it is determined that the level of the luminance signal is smaller than the reference value (step S3), the above (1)
As in the case of the above, the operation of the loop including step S7 is performed, the iris 1 is fully opened by generating the aperture control signal 71, and then the operation of the loop including step S8 is performed.
A gain control signal 73 is generated to control the gain of the analog AGC circuit 3. Thereby, the level of the luminance signal becomes equal to the reference value.

(3) When the illuminance of the subject changes from the area 2 in FIG. 4 to the area 3; as described above, in this area 2, the gain of the digital AGC circuit 5 is the minimum value, and the iris 1 is fully open. The gain of the analog AGC circuit 3 is between the maximum value and the minimum value. Therefore, first, when it is determined that the level of the luminance signal is smaller than the reference value (step S
3), the iris 1 is held in the fully open state (step S4), and the loop including step S8 is operated as described above to generate the gain control signal 73 to generate the analog AG signal.
The gain of the C circuit 3 is set to the maximum value. Analog AGC circuit 3
When the gain becomes the maximum value, the operation of the loop including step S9 is next performed to generate the gain control signal 75 to control the gain of the digital AGC circuit 5, whereby the level of the luminance signal becomes the reference value. Will be consistent.

The above is the case where the level of the luminance signal becomes lower than the reference value due to the change of the subject or the change of the imaging scene. If the level of the luminance signal becomes higher than the reference value, this is the case at step S3. , S10. As a result of this determination, the microcomputer 7 performs the following control operation.

(1) When the illuminance of the object changes from the area 3 in FIG. 4 to the area 1; as described above, in the area 3, the gain of the analog AGC circuit 3 is the maximum value, the iris 1 is in the fully open state, and the digital The gain of the AGC circuit 5 is between the maximum value and the minimum value. Therefore, first, when it is determined that the level of the luminance signal is higher than the reference value (step S10),
It is determined whether the gain of the digital AGC circuit 5 is a minimum value (step S11), and a gain control signal 75 for reducing the gain of the digital AGC circuit 5 is generated (step S1).
4) Send to the digital AGC circuit 5 during the blanking period. Such an operation, that is, steps S10, S11, S
A series of operations of S14, S16, S17, S2, and S3 is repeated until the gain of the digital AGC circuit 5 reaches a minimum value.

When this gain becomes the minimum value, it is next determined whether or not the gain of the analog AGC circuit 3 is the minimum value, and a gain control signal for reducing this gain is generated and supplied to the analog AGC circuit 3 during the blanking period. Send step S10, S1
The operation proceeds to repetition of a series of operations of 1, S12, S15, S16, S17, S2, and S3. When the gain becomes the minimum value, next, an aperture control signal 71 for reducing the iris 1 is generated and sent to the iris 1 during the blanking period (step S1).
0, S11, S12, S13, S16, S17, S2,
The process proceeds to repetition of a series of operations in S3. By such an operation, that is, by controlling the aperture amount of the iris 1, the level of the luminance signal becomes equal to the reference value.

(2) When the illuminance of the subject changes from region 3 to region 2 in FIG. 4; first, when it is determined that the level of the luminance signal is higher than the reference value (step S10), the gain of digital AGC circuit 5 Is determined to be a minimum value (step S11), a gain control signal 75 for reducing the gain of the digital AGC circuit 5 is generated (step S14), and sent to the digital AGC circuit 5 during a blanking period. Such operations are performed in steps S10, S11, S14, S1.
A series of operations of 6, S17, S2, and S3 are digital A
This operation is repeated until the gain of the GC circuit 5 reaches the minimum value.

When this gain becomes the minimum value, it is next determined whether or not the gain of the analog AGC circuit 3 is the minimum value, and a gain control signal 73 for reducing this gain is generated. S10, S to send to
The operation shifts to repeating a series of operations of 11, S12, S15, S16, S17, S2, and S3. During the repetition of this operation, the level of the luminance signal becomes equal to the reference value.

(3) When the illuminance of the subject changes from region 2 to region 1 in FIG. 4; as described above, in region 2, the gain of digital AGC circuit 5 is the minimum value, iris 1 is fully open, and analog The gain of the AGC circuit 3 is between the maximum value and the minimum value. Therefore, first, it is determined that the level of the luminance signal is larger than the reference value (step S10), and if the gain of the digital AGC circuit 5 is determined to be the minimum value (step S11), whether the gain of the analog AGC circuit 3 is the minimum value is determined. Is determined (step S12), and a gain control signal 73 for reducing the gain of the analog AGC circuit 3 is generated (step S15).
Send to This operation is performed in steps S10 and S1.
A series of operations of S1, S12, S15, S16, S17, S2, and S3 is repeated until the gain of the analog AGC circuit 3 reaches a minimum value. When this gain becomes the minimum value, next, an aperture control signal 71 for reducing the iris 1 is generated and sent to the iris 1 during the blanking period in steps S10 and S1.
The process proceeds to repetition of a series of operations of 1, S12, S13, S16, S17, S2, and S3. During the repetition of this operation, the level of the luminance signal becomes equal to the reference value.

In the control in the same region in FIG. 4, the loop operation including step S7 or S13 is repeated for the region 1 to control the aperture amount of the iris 1, and the region 2 is controlled in the step S7. S8 or S15
AGC circuit 3 by repeating the operation of the loop including
By controlling the gain of the digital AGC circuit 5 in the area 3 by repeating the operation of the loop including step S9 or S14,
It is performed respectively.

Next, the effect of quantization noise in this embodiment will be described. Now, the signal gain of the analog AGC circuit 3 is p, the signal gain of the digital AGC circuit 5 is q, and the sum of the signal gains of these AGC circuits 3 and 5 is k.
The noise generated by the sensor 2 is N _s , the quantization noise generated by the A / D converter 4 is N _q , the noise N _s and the quantization noise N
The ratio of _q to α is α, the noise in the automatic control device that includes only the analog AGC circuit 3 as the AGC circuit and amplifies the signal by k times is N _a , and the analog input signal is amplified by p times in the analog AGC circuit 3. , automatic control system of this embodiment to amplify the digital signal to q times a digital AGC circuit 5 (hereinafter, a hybrid of the automatic gain control device) when the noise at the N _d, the following equation (1) to (4) Is obtained. N _a ² = (k · N _s ) ² + Nq ² ····· (1) N _d ² = (k · N _s ) ² + (q · N _q ) ² ··· (2) N _s = α · N _q (3) k = p · q (4) The noise N _a, the ratio N of the size of N _d is expressed by the following equation (5). N = 10 · log (N _d ² / N _a ² ) [dB] (5) Further, from the expressions (1), (2) and (3), the following expression (1-
2) and the formula (2-2), the formulas (1-2) and (2-
The following equation (5-2) is obtained from 2) and (5). N _a ² = (k ² · α ² +1) N _q ² (1-2) N _d ² = (k ² · α ² + q ² ) N _q ² (2) -2) N = 10 · log {(k ² · α ² + q ² ) / (k ² · α ² +1)} (5-2).

Here, in the equation (5-2), in order to make the value of the ratio N close to 0, the value of k or α must be sufficiently larger than 1. In the formula (3), when a fixed value of noise N _s, in order to increase the value of α must reduce the value of the noise N _q. That is, it is necessary to sufficiently reduce the quantization noise N _q of the A / D converter 4 as compared to the noise N _s of sensors 2.

However, at present, some high-speed and low-power A / D converters suitable for use in video camera devices aiming at miniaturization, weight reduction and low power consumption include quantization noise. Nothing has the number of bits that can be made sufficiently small. Accordingly, since the value of α does not become sufficiently larger than 1, the influence of the signal amplification factor q of the digital AGC circuit 5 on N becomes large in the equation (5-2). That is, the influence of the quantization noise _Nq appears on the output image according to the signal amplification rate q of the digital AGC circuit 5.

However, if the signal amplification factor q of the digital AGC circuit 5 is suppressed to a certain extent, the deterioration of the output image can be kept within a visually acceptable range. Table 1 below assumes that the noise N _{s of the} sensor 2 and the quantization noise N _q of the A / D converter 4 are almost the same (α = 1), and furthermore, the threshold value, that is, the analog AGC circuit 3 Digital AGC when the maximum value of the signal amplification factor p is assumed to be 4.
A specific example showing a comparison result between noise when amplified by the circuit 5 alone and noise when amplified by the hybrid automatic gain control device is shown.

[0038]

[Table 1] As is apparent from Table 1, the digital AGC circuit 5
If the signal is amplified only by analog AGC
Since the noise when the signal is amplified only by the circuit 3 becomes almost twice as large, it is not suitable for practical use. However, noise when amplified by the hybrid automatic gain control device is amplified only by the analog AGC circuit 3 and not amplified by the digital AGC circuit 5 when the required amplification factor is equal to or less than the threshold value (k ≦ 4) (q
= 1), there is no effect of quantization noise due to amplification, and k
> 4, the digital AGC circuit 5 also amplifies (q>
1) Therefore, the influence of quantization noise due to amplification occurs. However, the analog AGC circuit 3 has a certain effect (4 times in Table 1).
Up to digital A
If the signal is amplified by the GC circuit 5, the digital AGC
The noise is greatly reduced as compared with the case where the signal is amplified only by the circuit 5, and the difference from the case where the signal is amplified only by the analog AGC circuit 3 is small. It can be said that it is within.

Further, the difference between N in the cases (i) and (ii) in Table 1 is only 0.05 dB, and the rate of deterioration due to quantization noise does not change so much even when the amplification factor k is increased. Therefore, above a certain threshold, digital AGC
It can be said that there is no problem even if the signal is amplified by the circuit 5.

As described above, in this embodiment, the conventional video camera apparatus is provided with the digital processing AGC circuit, and a part of the gain control operation conventionally performed in accordance with the analog processing AGC circuit is replaced with the analog processing. This is performed by an AGC circuit for digital processing that consumes less power, thereby reducing the power consumption of the video camera device.

FIG. 6 is a block diagram showing another embodiment of the automatic gain control circuit according to the present invention used in a video camera apparatus, wherein 5 'is a digital AGC circuit, 10 is a clamp circuit, and corresponds to FIG. The same reference numerals are given to the same parts, and the duplicate description will be omitted.

This embodiment differs from the embodiment shown in FIG. 1 in that, as shown in FIG. 6, in order to prevent the occurrence of underexposure during the automatic gain control processing, a certain offset indicating the black level is detected by a sensor. 2 in that a clamp circuit 10 is added to the output signal of No. 2 and the digital AGC circuit 5 'subtracts the black level due to this offset from the signal after the automatic gain control processing.

FIG. 7 is a block diagram showing a specific example of the digital AGC circuit 5 'in FIG. 6, wherein 516 is a subtractor, 517 is a latch circuit, and portions corresponding to those in FIG. ing.

In FIG. 7, the digital AGC circuit 5 'is different from the digital AGC circuit 5 shown in FIG.
And a latch circuit 517 for latching the output of the subtractor 516 with a latch pulse 75b.

Now, assuming that the value of the black level is k (k is an integer equal to or greater than 0), the subtractor 516 outputs the signal to the A / D converter 4 shown in FIG.
Subtracts the black level k from the m-bit digital signal 501 supplied from, and outputs an m′-bit (m ′ is a positive integer) -bit digital signal 504. This digital signal 5
04 is supplied to a multiplier 514 via a latch circuit 517, similarly to the digital AGC circuit 5 shown in FIG. 2. The digital signal 504 is a signal indicating the difference between the digital signal 501 and the black level k. Therefore, this is also the signal of the sign bit in the difference signal,
The control signal 503 is also supplied to the clamp circuit 10 as a control signal 503 indicating the result of comparing the level of the digital signal 501 with the black level k.

The microcomputer 7 also generates a control signal 710 indicating the timing at which the sensor 2 reads pixel data in the optical black section, and supplies the control signal 710 to the clamp circuit 10. The clamp circuit 10 receives the control signal 710 from the microcomputer 7.
, The level of the electric signal output from the sensor 2 is controlled according to the control signal 503 from the digital AGC circuit 5, and the digital signal 50 output from the subtractor 516 is controlled.
The level is 0 during the period of the control signal 710 every 4 horizontal cycles.
Adjust so that

Here, the reason why the subtractor 516 is provided before the multiplier 514 is that the reference level of the digital signal is set to 0 before the multiplier 514 amplifies the digital signal.
Otherwise, when the signal amplification rate changes, the black level fluctuates, and it becomes necessary to correct it. The actual setting of the black level is performed by setting the input / output characteristics of the limiter 52 to x = k in FIG. That is, the limiter 52 adds the amount k subtracted by the subtractor 516 to the input signal.

Other operations are the same as those of the digital AGC circuit 5 shown in FIG.

Therefore, in this embodiment, the same effect as that of the embodiment shown in FIG. 1 can be obtained, and the operation of the clamp circuit 10 and the digital AGC circuit 5 ′ causes the optical black section of the sensor 2 to be closed. When adjusting the black level during the period of the corresponding video signal, the digital A shown in FIG.
In the GC circuit 5 ', the reference level of the digital signal before the signal amplification by the multiplier 514 is set to 0, so that the black level fluctuation due to the signal amplification can be prevented.

FIG. 8 is a block diagram showing still another embodiment of the automatic gain control device, and portions corresponding to FIG. 1 are denoted by the same reference numerals.

This embodiment is not limited to the video camera device as in the above embodiment, but can be used for any device that keeps the output signal level of the signal processing circuit by digital processing constant. . The basic operation is the same as that of the embodiment shown in FIG.

That is, in this embodiment, since the gain control is performed by the two AGC circuits of the analog processing and the digital processing, it is possible to obtain a high gain with low power consumption as compared with the case where the gain control is performed only by the analog processing AGC circuit. Further, since the distribution of the gain of these AGC circuits is automatically controlled by the microcomputer, it is possible to obtain an output signal which is hardly affected by the quantization noise.

In each of the embodiments described above, A /
The quantization noise generated by the D converter 4 is digital AGC
In the case of low illuminance, the gain of the analog AGC circuit 3 is first increased in order to make the output image unnoticeable by the amplification by the circuit 5. A control method has been adopted in which the shortage is compensated for by the gain of the digital AGC circuit 5.
If the quantization noise is sufficiently smaller than the sensor noise generated from the sensor 2, the deterioration of the output image due to the amplification of the quantization noise by the digital AGC circuit 5 becomes inconspicuous. In low light, digital A
If the gain of the GC circuit 5 is increased and the required gain is equal to or larger than the threshold value, a control method may be adopted in which the shortage is compensated for by the gain of the analog AGC circuit 3.

[0054]

As described above, according to the present invention,
Since the maximum gain of the first variable gain amplifying circuit for amplifying an analog signal can be reduced, the circuit scale of the first variable gain amplifying circuit can be reduced, so that the power consumption can be reduced. Since the maximum gain of the second variable gain amplifying circuit for amplifying a digital signal can be reduced, the quantization noise generated thereby can also be reduced. As a result, since the power consumption of the second variable gain amplifying circuit is low, the gain of the first and second variable gain amplifying circuits can be sufficiently increased even when a high gain is required as in low-illumination photographing. Even when it is necessary to increase the value, automatic gain control can be performed with low power consumption, and generated quantization noise is small.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic gain control device according to the present invention used in a video camera device.

FIG. 2 is a block diagram showing a specific example of a digital AGC circuit in FIG.

FIG. 3 is a diagram illustrating input / output characteristics of a limiter in the digital AGC circuit illustrated in FIG. 2;

FIG. 4 is a characteristic diagram showing illuminance / AGC gain characteristics in the embodiment shown in FIG.

FIG. 5 is a flowchart showing an operation of the embodiment shown in FIG. 1;

FIG. 6 is a block diagram showing another embodiment of the automatic gain control device according to the present invention used in a video camera device.

FIG. 7 is a block diagram showing a specific example of a digital AGC circuit in FIG. 6;

FIG. 8 is a block diagram showing still another embodiment of the automatic gain control device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 iris 2 sensor 3 analog AGC circuit 4 A / D converter 5 digital AGC circuit 6 signal processing circuit 7 microcomputer 8 drive circuit 9 level detection circuit 10 clamp circuit

[Procedure amendment]

[Submission date] May 8, 2001 (2001.5.8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of the Invention] Video camera device

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

The present invention relates to a video camera device.
In particular, a video camera using an automatic gain control device
Apparatus about the.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

An object of the present invention is to solve such a problem,
It is an object of the present invention to provide a video camera device using an automatic gain control device having a good / N ratio, a small circuit scale, and low power consumption.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006]

In order to achieve the above object, the present invention converts input light into an analog electric signal.
A sensor for outputting an analog variable gain amplifying circuit for amplifying an output signal of the sensor with a gain corresponding to the first control signal, analog-to-digital converter for converting an output signal of the analog variable gain amplifying circuit into a digital signal Vessel and the
The output digital signal of the analog-to-digital converter is
A digital variable gain amplifier circuit for amplifying a gain corresponding to the control signal, and a signal processing circuit for generating a video signal by processing the output digital signal of the digital variable gain amplifier circuit, the output video signal of the signal processing circuit And a level detection circuit for detecting the level of the analog signal so that a value detected by the level detection circuit becomes equal to a preset reference value.
The first control signal for adjusting the gain of the variable gain amplifier circuit.
Signal and the gain of the digital variable gain amplifier circuit.
A control circuit for generating the second control signal .
The analog before being converted by the analog-digital converter
An offset indicating the black level is added to the electrical signal of the power supply.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a video camera device according to the present invention .
1 is a block diagram showing a basic configuration of an iris;
2 is a sensor, 3 is a variable gain amplifier circuit for analog processing (hereinafter, analog AGC circuit), 4 is an A / D (analog-digital) converter, 5 is a variable gain amplifier circuit for digital processing (hereinafter, digital AGC circuit). , 6 is a signal processing circuit, 7 is a microcomputer (hereinafter, referred to as a microcomputer), 8 is a drive circuit, and 9 is a level detection circuit.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction contents]

Next, the influence of quantization noise in the video camera device shown in FIG. 1 will be described. Now, the signal gain of the analog AGC circuit 3 is p, the signal gain of the digital AGC circuit 5 is q, the sum of the signal gains of the AGC circuits 3 and 5 is k, the noise generated by the sensor 2 is N _s , A
The quantization noise generated by the / D converter 4 is N _q and the noise N _s
Where α is the ratio of the noise to the quantization noise N _q , the noise in the automatic control device that includes only the analog AGC circuit 3 as the AGC circuit and amplifies the signal by k times is N _a , and the analog input signal is Amplifies p times, digital AG
This video amplifies a digital signal q times with C circuit 5
Automatic control device of the camera device (hereinafter, a hybrid of the automatic gain control device) when the noise at the N _d, equation (1) to (4) below is obtained. N _a ² = (k · N _s ) ² + N _q ² ····· (1) N _d ² = (k · N _s ) ² + (q · N _q ) ² ··· (2) N _s = α · N _q (3) k = p · q (4) N _a, the ratio N of the size of N _d is expressed by the following equation (5). N = 10 · log (Nd ² / Na ² ) [dB] (5) Further, from the equations (1), (2) and (3), the following equation (1-
2) and the formula (2-2), the formulas (1-2) and (2-
The following equation (5-2) is obtained from 2) and (5). N _a ² = (k ² · α ² +1) N _q ² (1-2) N _d ² = (k ² · α ² + q ² ) N _q ² (2) -2) N = 10 · log {(k ² · α ² + q ² ) / (k ² · α ² +1)} (5-2).

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

As described above, the video camera shown in FIG.
The device is a digital video processing A
A GC circuit is provided, and a part of the gain control operation conventionally performed according to the AGC circuit of the analog processing is replaced with the AGC of the digital processing that consumes less power than the analog processing.
The power consumption of the video camera device can be reduced.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

FIG. 6 is a block diagram showing an embodiment of a video camera apparatus according to the present invention , wherein 5 'is a digital AGC circuit, 10 is a clamp circuit, and parts corresponding to FIG. The same reference numerals are given and duplicate explanations are omitted.

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction contents]

This embodiment is a video camera shown in FIG.
The difference from the device is that, as shown in FIG. 6, a clamp circuit 10 for adding a certain offset indicating the black level to the output signal of the sensor 2 is provided in order to prevent the occurrence of blackout during the automatic gain control processing. To remove the black level due to this offset from the signal after automatic gain control processing,
The difference is that the digital AGC circuit 5 'performs the subtraction.

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0049

[Correction method] Change

[Correction contents]

Therefore, in this embodiment, the configuration shown in FIG.
The same effect as that of the video camera device can be obtained, and when the black level of the video signal period corresponding to the optical black section of the sensor 2 is adjusted by the operation of the clamp circuit 10 and the digital AGC circuit 5 ′, In the digital AGC circuit 5 'shown in FIG. 7, the reference level of the digital signal before the signal amplification by the multiplier 514 is set to 0, so that the black level fluctuation due to the signal amplification can be prevented.

[Procedure amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction contents]

FIG. 8 is a block diagram showing still another example of the automatic gain control device, and portions corresponding to FIG. 1 are denoted by the same reference numerals.

[Procedure amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0051

[Correction method] Change

[Correction contents]

This example is not limited to the video camera device as described above, but can be used for any device that keeps the output signal level of the signal processing circuit by digital processing constant. The basic operation is the same as that of the video camera device shown in FIG.

[Procedure amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction contents]

That is, in this example , since the gain control is performed by two AGC circuits for analog processing and digital processing, a higher gain can be obtained with lower power consumption than when gain control is performed only by the AGC circuit for analog processing. Further, since the distribution of the gain of these AGC circuits is automatically controlled by the microcomputer, it is possible to obtain an output signal which is hardly affected by the quantization noise.

[Procedure amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction contents]

In the automatic gain control device described above, it is conspicuous that the quantization noise generated in the A / D converter 4 is amplified by the digital AGC circuit 5 so that the output image is deteriorated. In order to eliminate the illuminance, the gain of the analog AGC circuit 3 is first increased in the case of low illuminance.
A control method has been adopted in which the gain is compensated by the gain of the circuit 5. However, if the quantization noise is sufficiently smaller than the sensor noise generated from the sensor 2, the quantization noise is amplified by the digital AGC circuit 5. The deterioration of the output image caused by the AGC circuit 3 becomes inconspicuous, so that the positions of the analog AGC circuit 3 and the digital AGC circuit 5 are reversed, and in low illuminance, the gain of the digital AGC circuit 5 is increased first, and the required gain is higher than the threshold value. In this case, a control method may be adopted in which the shortage is supplemented by the gain of the analog AGC circuit 3.

[Procedure amendment 16]

[Document name to be amended] Statement

[Correction target item name] 0054

[Correction method] Change

[Correction contents]

[0054]

As described above, according to the present invention,
Since the maximum gain of the analog variable gain amplifying circuit for amplifying the analog signal can be reduced, it is possible to reduce the circuit scale of the analog variable gain amplifying circuit, Therefore, to can be suppressed to be small power consumption, also the analog variable Profit
The output signal of the gain amplifier is converted by an analog-to-digital converter.
Since the maximum gain of the digital variable gain amplifying circuit for amplifying the digital signal obtained by the conversion can be reduced, the quantization noise generated thereby can be reduced.
As a result, since the power consumption of the digital variable gain amplifier circuit is low, automatic gain control can be performed with low power consumption even when high gain is required as in low-illumination shooting, and the generated quantization noise is reduced. Is also reduced. And the analog
-The analog signal before conversion by the digital converter is black.
Since the offset indicating the level is added,
It is possible to prevent blackout occurring during the above processing.

[Procedure amendment 17]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 shows a video according to the invention using an automatic gain control device .
FIG. 2 is a block diagram illustrating a basic configuration of the camera device .

FIG. 2 is a block diagram showing a specific example of a digital AGC circuit in FIG.

FIG. 3 is a diagram illustrating input / output characteristics of a limiter in the digital AGC circuit illustrated in FIG. 2;

[4] illumination / AGC of the automatic gain control apparatus definitive 1
FIG. 4 is a characteristic diagram illustrating gain characteristics.

5 is a flowchart illustrating the operation of the automatic gain control apparatus definitive in FIG.

FIG. 6 is a block diagram showing an embodiment of a video camera device according to the present invention .

FIG. 7 is a block diagram showing a specific example of a digital AGC circuit in FIG. 6;

FIG. 8 is a block diagram showing another example of the device using the automatic gain control device .

[Description of Signs] 1 Iris 2 Sensor 3 Analog AGC circuit 4 A / D converter 5 Digital AGC circuit 6 Signal processing circuit 7 Microcomputer 8 Drive circuit 9 Level detection circuit 10 Clamp circuit

Continuing from the front page (72) Inventor Hiroyasu Otsubo 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in the Visual Media Research Laboratory, Hitachi, Ltd. 5C021 PA12 PA17 PA66 PA67 RB01 XA13 XA41 5C022 AA11 AB06 AC56 AC69 5J022 AA01 BA02 BA06 BA08 CC02 CE08 CF01 CF02 CF10 CG01 5J100 JA01 KA05 LA07 LA09 LA11 LA13 QA01

Claims (1)

[Claims] A first variable gain amplifying circuit for amplifying the input signal with a gain according to a first control signal, and an output signal of the first variable gain amplifying circuit; An analog-to-digital converter for converting the digital signal output from the analog-to-digital converter with a gain according to a second control signal;
A variable gain amplifier circuit, a signal processing circuit for processing an output digital signal of the second variable gain amplifier circuit, a level detection circuit for detecting a level of an output signal of the signal processing circuit, and detection by the level detection circuit A control circuit for generating the first and second control signals for setting the gains of the first and second variable gain amplifier circuits so that the value becomes equal to a preset reference value. An automatic gain control device characterized by the above-mentioned.