JP3072043B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device such as a video camera.

[0002]

2. Description of the Related Art Generally, a CCD (charge c.
Automatic gain control circuit that controls the gain of an amplifier that amplifies the electric signal output from the CCD so that the level of the output signal of the imaging device does not change even if the amount of light incident on the solid-state imaging device changes. (Hereinafter referred to as “AGC circuit”) (for example, see Japanese Patent Application Laid-Open No. 63-3067).
No. 75, the output signal is automatically amplified to a certain level even when the illuminance is lowered. This is referred to as a first conventional example.

On the other hand, conventionally, as a method of increasing the sensitivity at low illuminance, there is a method of delaying a video signal in a memory and performing cumulative addition (Japanese Patent Laid-Open No. 5-103266). An imaging apparatus using this method is referred to as a second conventional example. Hereinafter, first and second conventional examples will be described with reference to the drawings. FIG. 12 is a block diagram showing a basic configuration of the imaging device of the first conventional example.

In the imaging apparatus shown in FIG. 12 , an electric signal from a solid-state imaging device 101 is input to a variable gain amplifier 102, amplified by the variable gain amplifier 102, and output as an output signal S4.
And sent to the level detection circuit 103. The level detection circuit 103 includes a variable gain amplifier 102
The level of the output signal S4 is detected. The gain control circuit 104 compares the level signal from the level detection circuit 103 with a target value, and controls the gain of the variable gain amplifier 102 so that the level signal and the target value become equal. As a result, even if the illuminance decreases, the gain control circuit 104 increases the gain of the variable gain amplifier 102, thereby keeping the level of the output signal S4 constant.

FIG. 13 is a block diagram showing a basic configuration of a second conventional imaging apparatus. In the imaging apparatus of FIG. 13 , an analog video signal from an imaging unit 111 having a solid-state imaging device such as a CCD is converted into a digital video signal S5 by an analog / digital converter (hereinafter, referred to as an “A / D converter”) 112. Is converted to Memory unit 11
5 stores the output video signal S6. The multiplier 113
A constant 1-A (A is 0 <A <1) set by the constant setting circuit 117 in the output signal S5 from the AD converter 112.
To normalize the signal level. The multiplier 11
Numeral 6 normalizes the signal level by multiplying the output signal from the memory unit 115 by a constant A set by the constant setting circuit 117. Then, the adder 114 adds the output signals from the multipliers 113 and 116 and outputs the result as an output video signal S6. By repeating the addition in the adder 114, for example, the signal level of the output video signal S6 is changed to S _i ,
Assuming that the noise level is N _i , the signal level S _o of the output video signal S 6 is the sum of the amplitudes.

[0006]

(Equation 1)

[0007], and the noise level N _o is the power sum,

[0008]

(Equation 2)

Therefore, at the average amplitude,

[0010]

(Equation 3)

Therefore, the signal-to-noise ratio (hereinafter “S / N”)
Ratio))

[0012]

(Equation 4)

As a result, the S / N ratio is improved, so that the sensitivity substantially increases even at low illuminance.

[0014]

However, in the configuration of the first conventional example, when the illuminance decreases, the gain of the variable gain amplifier 102 simply increases, so that the S / N ratio is reduced. Will deteriorate. Therefore, in general, the maximum value of the gain of the variable gain amplifier 102 is determined in consideration of the deterioration of the S / N ratio so that the gain of the variable gain amplifier 102 does not exceed the maximum value even when the illuminance decreases. ing. In this case, the gain does not increase even if the illuminance falls below the maximum value of the gain, so that the output signal level cannot be kept constant.

Further, in the configuration of the second conventional example, the S / N ratio is improved as described above, so that the sensitivity is substantially increased even at low illuminance, but the actual output signal level is reduced by the input signal level. In addition to the level, the signal does not increase and the past signal delayed by the memory unit 115 is multiplied by a constant A (0 <A <1).
Since the signal is added to the current signal (1-A times the actual signal), if there is a motion in the video signal, the influence of the past video signal remains, that is, an afterimage occurs.

The present invention solves the above-mentioned conventional problems, and provides an imaging apparatus capable of keeping the output signal level constant while minimizing the deterioration of the S / N ratio and the afterimage even at low illuminance. The purpose is to:

[0017]

According to a first aspect of the present invention, there is provided an image pickup apparatus comprising: a solid-state image pickup device for converting incident light into an electric signal; an amplifying means for amplifying an electric signal; and a delay for delaying an input signal for a predetermined period. Means, multiplication means for multiplying the output signal from the delay means by a set value, and an adder for adding the output signal from the multiplication means and the output signal from the amplification means and outputting to the delay means. A level detecting means for detecting a level of an output signal from the amplifying means, and a gain of the amplifying means being controlled so that the level signal from the level detecting means becomes equal to its target value, and the gain is increased to a predetermined value. Control means for reducing the target value when reaching the value and increasing the value to be multiplied by the multiplication means, the output of the adder or the delay means.
Maintaining the signal level substantially constant, so that the output signal of the output signal to the outside.

According to this configuration, when the gain increases and reaches a predetermined value, the target value of the level signal is reduced and the value multiplied by the multiplication means is increased, thereby suppressing the after-image phenomenon of the output signal. It is possible to suppress the deterioration of the S / N ratio due to the signal amplification of the amplifying means at the time of low illuminance, and to keep the output signal level constant. An imaging device according to claim 2, wherein the solid-state imaging device converts incident light into an electric signal,
Amplifying means for amplifying an electric signal; delay means for delaying an input signal for a predetermined period; multiplying means for multiplying an output signal from the delay means by a set value; and an output signal from the multiplying means. An adder for adding the output signal from the amplifying means and outputting the result to the delay means; a level detecting means for detecting a level of the output signal from the amplifying means; and a level signal from the level detecting means being equal to its target value. controlling the gain of the amplifying means so that, reduce the target value with a decrease in the illuminance of the incident light, and a control means for increasing the value to be multiplied with the multiplication means, the output signal of the adder or the delay means
Maintaining the level substantially constant, so that the output signal of the output signal to the outside.

According to this configuration, by reducing the target value of the level signal and increasing the value to be multiplied by the multiplication means in accordance with the decrease in the illuminance of the incident light, the S / A by the signal amplification of the amplification means at low illuminance is obtained. It is possible to suppress the deterioration of the N ratio and to keep the output signal level constant. Also,
As the illuminance decreases, the gain of the amplifying means and the value multiplied by the multiplying means gradually increase, and the afterimage phenomenon of the output signal can be suppressed.

According to a third aspect of the present invention, in the imaging apparatus of the second aspect, the control means detects the level when the gain of the amplifying means or the illuminance of incident light is within a predetermined range.
A target value of the level signal from the means and a value to be multiplied by the multiplying means are fixed. According to this configuration, the gain of the amplifying means or the illuminance of the incident light falls within a predetermined range according to the level of the S / N ratio and the degree of afterimage.
By fixing the target value of the signal and the value to be multiplied by the multiplying means, the afterimage phenomenon can be further suppressed.

According to a fourth aspect of the present invention, in the imaging apparatus of the second aspect, the control means fixes the gain at a predetermined gain value when the gain of the amplification means reaches a predetermined gain value, When the value to be multiplied by the multiplying means reaches a predetermined value, the value to be multiplied is fixed at a predetermined value, and the fixed gain and the fixed multiplied value are performed in different ranges of the illuminance of incident light. And

According to this configuration, by fixing the gain of the amplifying means and fixing the value to be multiplied by the multiplying means in accordance with the deterioration of the S / N ratio and the degree of the afterimage, the deterioration of the S / N ratio is reduced. The afterimage phenomenon can be further suppressed.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of the imaging apparatus according to the first embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a solid-state imaging device such as a CCD, 12 denotes a variable gain amplifier as amplifying means for amplifying an analog electric signal S1 from the solid-state imaging device 11, 1
Reference numeral 3 denotes an A / D converter for converting an analog signal from the variable gain amplifier 12 into a digital signal, and reference numeral 14 denotes an A / D converter 13
Adder for adding the output signal S2 from the adder to the signal from the multiplier 16, 15 is a field memory as delay means for delaying the output signal from the adder 14 by one field, and 16 is an output from the field memory 15 A multiplier as a multiplying means for multiplying the signal S3 by a multiplier k (0 <k <1), 17 is a level detecting means for detecting the signal level of the signal S2, and 18 is a level signal S _av from the level detecting means 17.
The gain G of the variable gain amplifier 12 and the multiplier 1
This is system control means for controlling the value k to be multiplied by 6. As the system control means 18, for example, a microcomputer can be used.

The analog video signal S1 from the solid-state imaging device 11 is amplified by the variable gain amplifier 12 with a gain G, and further converted by the A / D converter 12 into a digital video signal S2. The signal S2 and the output from the multiplier 16 are added by the adder 14 and input to the field memory 15. The multiplier 16 includes the field memory 1
5 is multiplied by k and output to the adder 14. On the other hand, the level detecting means 17 obtains an average value of a predetermined period of the signal S2, for example, one field period,
The level of the signal S2 is detected and output as a level signal _Sav . The system control means 18 determines the gain G of the variable gain amplifier 12 and the multiplier 1 based on the level signal _Sav.
The control of the multiplier k of 6 is performed. First, it will be described that the level and the S / N ratio of the output signal S3 change by this control.

[0025] For example, the level of the analog signal S1 is set to a constant value S _a, level S _x of the signal S2, and the level of the output signal S3 When S _y,

[0026]

(Equation 5)

[0027]

(Equation 6)

The next level S _x of the signal S2, G times the level S _a of the analog signal S1 and the level S _y of the output signal S3, the first level S _x of the signal S2 with time
/ (1-k) times. Similarly, the noise level of the signal S2 N _x, the noise level of the output signal S3 and N _y,

[0029]

(Equation 7)

The next, the noise level N _y enough over time and the output signal S3 is compared with the noise level N _x of the signal S2, 1 / (1-k 2) times the power level, the average amplitude 1 / (1-k ²⁾ becomes ^1/2 times. Therefore, the S / N ratio of the output signal S3 is

[0031]

(Equation 8)

The signal S2 has an S / N ratio of 信号 (1+
k) / (1−k)｝ is improved by a factor of ^1/2 . However, since the cumulative sum of the past signal S2 multiplied by k is added to the signal S2 of the current field, if the signal S2 has motion as a video, an afterimage occurs in the output signal S3. Amplification gain on the level S _x level S _y of the signal S2 output signal S3 when the multiplier k is changed

[0033]

(Equation 9)

This is shown in FIG. 2A. Similarly, S / of output signal S3 when multiplier k changes.
The degree of improvement of the S / N ratio of the N ratio signal S2 is

[0035]

(Equation 10)

This is shown in FIG. 2B. For example, when k = 1/2

[0037]

[Equation 11]

[0038]

(Equation 12)

And when k = 3/4,

[0040]

(Equation 13)

[0041]

[Equation 14]

Is as follows. Next, the operation of the system control means 18 will be described with reference to FIG. FIG. 3 is a flowchart showing the operation of the system control means 18. At the start of operation, the gain G is set to 1 and the multiplier k is set to 0 (see FIG. 3).
(1)). Furthermore, S _tg which is a target value of the level signal S _av from the level detecting means 17 is set to the value S _kp to output signal S3 is maintained (Fig. 3 (2)). The system control means 18 first obtains the level signal _Sav from the level detection means 17 (FIG. 3- (3)). And comparing the level signal S _av and the target value S _tg, resulting from the system control unit 18 is changed to the value calculated gain G such that S _av = S _tg (Fig 3 (4)) . Thereby, the level _{Sx of the} signal S2 is kept near _Stg , that is, _Skp . Multiplier k of the multiplier 16 is the first 0, since the signal S2 is directly the output signal S3, the level S _y of course the output signal S3 is also kept near the S _kp. If only the operation up to this point, the conventional A
It is similar to the operation of the GC circuit and is well known,
Detailed description of the operation is omitted.

The operation from here will be described with reference to FIG.
FIG. 4 is a characteristic curve diagram showing the control of various variables with respect to the decrease in illuminance by the system control means 18. As the illuminance decreases, the gain G increases steadily, thereby increasing the S / S of the signal S2.
The N ratio deteriorates. Therefore, first, the maximum gain _{Gmax at} which the deterioration of the S / N ratio falls within the allowable range is set in advance. When the illuminance is reached gradually decreases in going from point A to point B in FIG. 4 (a), the level signal S _av by level detecting means 17, the system control unit 18 is the gain G reaches a G _max to be set (Fig. 3- (5)). Then, the system control means 18 first sets the target value _Stg to _Skp / 2 as shown in FIG.
(FIG. 3- (6)), and at the same time, increase the multiplier k of the multiplier 16 from 0 to １ ／ as shown in FIG. 4 (d) (FIG. 3- (7)). Thereafter, the AGC operation is continued.

With the above control, the level S _{x of the} signal S2 is obtained.
_Drops to near the target value _Stg, ie, _Skp / 2. on the other hand,
2 × As multiplier k is level S _y of the output signal S3 because it increased to 1/2, stand time as shown in equation (11)
It approaches _Sx . Therefore, even if the illuminance further decreases, S _x is kept near S _kp / 2, so that S _y is 2
It can be seen that × S _x = S _kp is maintained. Also, the S / N ratio deterioration due to the decrease in illuminance and the increase in the gain G is improved by about 4.8 [dB] as shown in (Equation 12) by increasing the multiplier k of the multiplier 16 to １ ／. You.

Further, AGC is performed with the target value _Stg = _Skp / 2.
It continues to operate, when the illuminance reaches the point C of FIG. 4 (a), again the gain G becomes G _max is FIG 4 (c), (d)
Then, the target value _Stg is decreased to _Skp / 4, and the multiplier k is increased to 3/4, and then the AGC operation is performed.
Whereby as the level S _y of the output signal S3 shown in equation (13), 4 × S _x, i.e. maintained at 4 × S _tg = S _kp, whereas, deterioration of S / N ratio, (Equation 14) Approximately 8.5 dB is improved as shown in FIG.

When the illuminance further decreases, the target value _Stg is set to _Stg = _Skp / ²ⁿ , and the multiplier k of the multiplier 16 k = 1- (1 /
2) ^{n (n:} G is by performing the same control as the number of times) that reaches the G _max, while suppressing the S / N ratio degradation due to illumination intensity and variable gain amplifier 12, the level S of the output signal S3
_y can be kept at a constant value S _kp . The multiplier 16
Is multiplied stepwise as the illuminance decreases, so that the afterimage of the output video signal S3 when the video signal S2 moves can be minimized.

When the illuminance rises at least once after the illuminance has fallen and the gain G has reached _Gmax , the control reverse to the above control is performed. For example, _Stg =
If the illuminance is increased when the _{S kp / 2, k = 1} /2, the gain G is decreased, returning to _{S tg = S kp, k =} 0 at the time the G drops to G _{ma x} / 2, Then, the AGC operation may be continued.

In this embodiment, the gain G is G
The target value _Stg when it _reaches the _maximum is _Stg = _Skp / 2
^n: While set at (n G is the number of times reaches the G _max), it is not always necessary to do so, short S _tg = S _kp / b
^{When n} is set, 1 <b and k = 1− (1 / b) ⁿ may be used.

[0049]

[0050]

Further, in this embodiment, the multiplier 16 is used as the multiplying means, but the multiplier k = 1− (1/2) ⁿ
And the maximum value of n is determined, FIG.
A circuit having such a configuration can be used as multiplication means. In that case, a reduction in circuit scale can be expected as compared with the above embodiment. In FIG. 11 , 41-1 to 41-n
Is a bit shift means, 42 is a selector, and 43 is a subtractor.

[0052]

Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is the same as the configuration of the first embodiment shown in FIG. 1, and the description of FIG. 1 is omitted. The second embodiment differs from the first embodiment in the control method of the system control unit 18. Hereinafter, a control method of the system control unit 18 according to the second embodiment will be described with reference to FIGS. FIG. 5 is a flowchart showing the operation of the system control means 18 according to the second embodiment. FIG. 6 is a characteristic curve diagram showing the control of various variables with respect to the decrease in illuminance of the system control means 18 according to the second embodiment.

The system control means 18 first detects the level
Level signal S from the means 17_avAnd the target value S_tgCompare with
However, the target value S_tgThe output signal S3 should be kept
Value S _kpFor S_tg= A × S_kp(0 <a ≦ 1)
At the start of operation, a = 1, that is, S_tg= S_kpSet aside
Good. The value k to be multiplied by the multiplier 16 is given by k = 1−a.
When the operation starts, k = 0 (FIG. 5- (1)). Soshi
The coefficient a used here is changed according to the decrease in illuminance.
(D). However, here is the current illuminance
, But here the level signal S_avThe level
After being obtained from the detecting means 17 (FIG. 5- (2)), the gain is increased.
S divided by the gain G of the width unit 12_av/ G (Fig. 5-
(3)), used as illuminance. The gain at the start of operation
The gain G of the variable amplifier 12 is 1.

When the illuminance, that is, S _av / G, gradually decreases from the point A in FIG. 6A, the coefficient a is gradually reduced accordingly as shown in FIG. −
(4)). The target value _Stg is _Stg = a x _Skp , and the multiplier k is k =
Because they set to 1-a (Fig. 5 (5)), and gradually decreases the value of the multiplier k reversed from S _kp as shown in FIG. 6 is a target value S _tg (c) by reduction of the coefficient a As shown in FIG.
And gradually increase.

The system control means 18 then determines S _av and S
comparing the _tg, since the conventional AGC operation of changing its value seeking gain G such that S _av = S _tg (Fig 5 (6)), the level S _x of the signal S2 target The value is kept near the value _Stg , that is, a * _Skp . Output signal S3
The level S _{y of} is given by (Equation 9)

[0057]

(Equation 16)

Where 1−k = a,

[0059]

[Equation 17]

Is as follows. In other words, S _y is kept in the vicinity of S _kp. On the other hand, the deterioration of the S / N ratio due to the decrease in the illuminance and the signal amplification of the variable gain amplifier 12 is also improved as in the first embodiment (Equation 10) by the increase of the multiplier k with the decrease of the coefficient a. You. Further, both gain G and multiplier k gradually increase due to the above control, so that S / N
The deterioration of the ratio and the afterimage generated in the output signal S3 when there is a motion in the video can be suppressed as much as possible.

[0061]

Next, a third embodiment of the present invention will be described. The configuration of the third embodiment is the same as the configurations of the first and second embodiments shown in FIG. 1, and the description of FIG. 1 is omitted. The third embodiment differs from the first and second embodiments in the control method of the system control unit 18. Hereinafter, a control method of the system control unit 18 according to the third embodiment will be described with reference to FIG. FIG. 7 is a characteristic curve diagram showing the control of various variables with respect to the decrease in illuminance of the system control means 18 in the third embodiment.

[0063] The system control unit 18, like the second _{embodiment, S tg = a × S kp} (0 for values S _kp should the target value S _tg output signal S3 is maintained <a ≦ 1 ), The value k to be multiplied by the multiplier 16 is set to k = 1−a, and at the start of operation, a = 1, that is, _Stg = _Skp , k = 0. The fixed target value S _tg to S _kp, a, k remains the 1,0 respectively fixed, only the control of the gain G by the first conventional AGC operation. Then, the illuminance gradually decreases from the point A in FIG. 7A, and when the illuminance reaches the point B where the gain G of the variable gain amplifier 12 becomes G = _GL by the AGC operation, the fixed a = 1 is released. 5 (2) to (6) described in the second embodiment. By this control, the coefficient a and the target value _Stg decrease and the multiplier k increases as shown in FIGS. 7C and 7D according to the decrease in the illuminance. Then, as described in the second embodiment, the level S _y of the output signal S3 is maintained at around S _kp, S / N ratio of the output signal is improved. However, the value of the gain _GL at which the coefficient a starts decreasing, that is, the increase of the multiplier k, is determined according to the degree of deterioration of the S / N ratio of the output signal S3 due to the decrease in illuminance and the signal amplification of the variable gain amplifier 12. (For example, the value of the gain G when the S / N ratio falls by 6 dB).

With the above control, the multiplier k of the multiplier 16
Can be set to 0 until the S / N ratio of the output signal S3 is degraded to some extent. Therefore, when the illuminance is such that the degradation of the S / N ratio is not so problematic, the afterimage can be eliminated, which is effective. In this embodiment, the gain G of the variable gain amplifier 12 is
Starts decreasing the coefficient a when G reaches G _L , that is, increases the multiplier k. When the illuminance S _av / G reaches L as shown in FIG. You may.

FIG. 7D shows a change in the coefficient a with respect to the decrease in the illuminance. In this figure, the coefficient a monotonously decreases when the illuminance decreases below the point B. The present invention is not particularly limited to this, and may be kept constant during a certain period T as shown in FIG. 8C according to the deterioration of the S / N ratio of the output signal S3 and the degree of afterimage. In this case, an afterimage generated in the output signal S3 can be suppressed as compared with the second embodiment. Note that the period T is _{equal to the} gain G or the illuminance S _av /
What is necessary is just to set by the value of G.

[0066] Next, a fourth embodiment of the present invention will be described.
Will be explained. The configuration of the fourth embodiment is similar to the configuration shown in FIG.
The configuration is the same as that of the first, second and third embodiments.
Is omitted. The fourth embodiment is the first, second, and second
The difference from the third embodiment is that the system control means 18
It is a control method.

A system according to the fourth embodiment will be described below.
The control method of the control means 18 will be further described with reference to FIG.
I will explain it. FIG. 9 shows a system according to the fourth embodiment.
The control of various variables with respect to the illuminance reduction of the system control means 18 is shown.
FIG. The system control means 18 includes:
As in the third embodiment, the target value S_tgOutput signal S3
S that should be kept_kpFor S_tg= A × S_kp(0 <a
≦ 1), the value k to be multiplied by the multiplier 16 is set to k = 1−a
When the operation starts, the coefficient a = 1, that is, S _tg= S_kp, K =
Set to 0. And the target value S_tgS_kpAnd a and k are
First, the conventional AGC operation
Only the gain G is controlled.

Then, the illuminance gradually decreases from point A in FIG. 9A, and the variable gain amplifier 1
When the gain G of 2 reaches the point B at which the gain becomes G ₁ , a is set to a = S _av / S _kp using the value of the level signal S _av of the level detecting means 17 from a = 1 fixed. On the other hand, the gain G is fixed with G _1, interrupts the AGC operation. When the illuminance decreases, the gain G is fixed, so that S _av decreases, that is, the coefficient a decreases.
The multiplier k is

[0069]

(Equation 18)

Therefore, it increases. Level S _y of the output signal S3 from the equation (16)

[0071]

[Equation 19]

Is obtained. S_avIs the level S of the signal S2_xOf 1
Since it represents the average during the field period, the output signal
Level S of S3_yIs S_kpKept near. Also, the multiplier k
The S / N ratio deterioration of the output signal S3 is also improved by the increase of
You. The illuminance further decreases and the coefficient a = a₁Reaches point C
Then, this time, a₁And the target value S_tgThe figure
A as in 9 (c)₁× S_kpAfter changing to the system
The AGC operation of the control means 18 is restarted. Thereby
Level S of signal S2 _xIs the target value S_tgIe, a₁× S
_kpIs kept close to the output signal S3._yIs

[0073]

(Equation 20)

And is kept near S _kp . Further lower the illuminance, when the gain G reaches G ₂ is, interrupts the AGC operation, to fix the gain G, to vary the coefficient a at a = S _av / S _kp. On the other hand, when the coefficient a reaches a ₂ , a is fixed, the target value is changed to _Stg = a ₂ × S _kp , and A
Restart the GC operation. Further, when the gain G reaches G ₃ are, the same control as when it reaches the G _2. That is, when the coefficient a is variable, that is, when the multiplier k of the multiplier 16 is variable, the AGC operation is interrupted and the gain G is fixed. Conversely, when the multiplier k is fixed, the AGC operation is performed to control the gain G to be changed.

With the above control, the values of the gain G and the coefficient a (G ₁ and a ₁ ) for changing the gain G and the coefficient a (multiplier k) from fixed to variable or from variable to fixed are output signal S
3 makes it possible to further suppress the deterioration of the S / N ratio of the output signal S3 and the afterimage as compared with the third embodiment by appropriately setting the S / N ratio deterioration and the degree of the afterimage. Become.

In this embodiment, one of the coefficient a (multiplier k) and the gain G is made variable and the other is fixed. However, as shown in FIG. It goes without saying that both may be changed after the predetermined period as described above.

In the first to fourth embodiments,
Although the output of the field memory 15 is extracted as an output video signal, the output of the adder 14 may be extracted as an output video signal. Further, the delay period of the field memory 15 is set to one field. However, the present invention is not limited to this, and n fields or n frames (n = 1, 2, 2) are used.
3,...).

[0078]

According to the first aspect of the present invention, the control means controls the gain of the amplifying means so that the level signal becomes equal to the target value, and the gain of the amplifying means increases to reach a predetermined value. Sometimes, by reducing the target value of the level signal and increasing the value to be multiplied by the multiplying means, the after-image phenomenon of the output signal is suppressed, and the deterioration of the S / N ratio due to the signal amplification of the amplifying means at low illuminance is suppressed. , The output signal level can be kept constant.

According to a second aspect of the present invention, in the imaging apparatus, the control means includes:
Level signal to control the gain of the amplifying means to be equal to the target value, the level signal in response to a decrease in the illuminance of the incident light
By reducing the target value and increasing the value to be multiplied by the multiplication means, it is possible to suppress the deterioration of the S / N ratio due to the signal amplification of the amplification means at low illuminance and to keep the output signal level constant. Further, as the illuminance decreases, the gain of the amplifying means and the value multiplied by the multiplying means gradually increase, and the afterimage phenomenon of the output signal can be suppressed.

According to a third aspect of the present invention, in the imaging apparatus of the second aspect, the control means detects the level when the gain of the amplifying means or the illuminance of incident light is within a predetermined range.
By which is adapted to secure the target value and the value to be multiplied with the multiplication means level signal from the means, it is possible to further suppress the residual image phenomenon.

According to a fourth aspect of the present invention, in the imaging apparatus of the second aspect, the control means fixes the gain at a predetermined gain value when the gain of the amplification means reaches a predetermined gain value, When the value to be multiplied by the multiplying means reaches a predetermined value, the value to be multiplied is fixed at a predetermined value, and the fixed gain and the fixed multiplied value are performed in different ranges of illuminance of incident light, By fixing the gain of the amplifying means and fixing the value to be multiplied by the multiplying means in accordance with the degree of S / N ratio deterioration and the degree of afterimage, deterioration of the S / N ratio and the afterimage phenomenon can be further suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an imaging device according to an embodiment of the present invention.

FIG. 2 is a characteristic curve showing the level ratio of output signals S3 and S2 and the degree of improvement of the S / N ratio when multiplier k of multiplier 16 changes in the embodiment of the present invention.

FIG. 3 is a flowchart illustrating an operation of a system control unit according to the first embodiment of the present invention.

FIG. 4 is a characteristic curve diagram showing control of various variables with respect to reduction in illuminance of a system control unit according to the first embodiment of the present invention.

FIG. 5 is a flowchart illustrating an operation of a system control unit according to the second embodiment of the present invention.

FIG. 6 is a characteristic curve diagram showing control of various variables with respect to a decrease in illuminance by a system control unit according to the second embodiment of the present invention.

FIG. 7 is a characteristic curve diagram illustrating an example of control of various variables with respect to a decrease in illuminance by a system control unit according to a third embodiment of the present invention.

FIG. 8 is a characteristic curve diagram illustrating an example of control of various variables with respect to a decrease in illuminance of a system control unit according to a third embodiment of the present invention.

FIG. 9 is a characteristic curve diagram illustrating an example of control of various variables with respect to reduction in illuminance of a system control unit according to a fourth embodiment of the present invention.

FIG. 10 is a characteristic curve diagram illustrating an example of control of various variables with respect to a decrease in illuminance of a system control unit according to a fourth embodiment of the present invention.

FIG. 11 shows one example of a multiplication means in the embodiment of the present invention .
It is a figure showing an example.

FIG. 12 shows a basic configuration of a first conventional imaging apparatus.
FIG.

FIG. 13 shows a basic configuration of a second conventional imaging apparatus.
FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 11 solid-state imaging device 12 variable gain amplifier (amplifying means) 13 A / D converter 14 adder 15 field memory (delaying means) 16 multiplier (multiplying means) 17 level detecting means 18 system control means (control means) 41-1 ~ 41-n bit shift means 42 selector 43 subtractor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-290380 (JP, A) JP-A-4-156075 (JP, A) JP-A-1-318467 (JP, A) JP-A-1-290467 122273 (JP, A) Japanese Utility Model Application Hei 1-93878 (JP, U) Japanese Utility Model Application Hei 2-128472 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/30-5 / 335 H04N 5/14-5/217

Claims (4)

(57) [Claims] 1. A solid-state imaging device that converts incident light into an electric signal, an amplifying unit that amplifies the electric signal, a delay unit that delays an input signal for a predetermined period, and an output signal from the delay unit. Multiplying means for multiplying the output signal from the multiplying means and the output signal from the amplifying means and adding the output signal to the delay means; and the level of the output signal from the amplifying means. And a gain detecting means for controlling the gain of the amplifying means so that the level signal from the level detecting means becomes equal to the target value. When the gain increases and reaches a predetermined value, the target value is obtained. Smaller
And control means for increasing the value to be multiplied by the multiplying means, wherein the output signal level of the adder or the delay means is substantially equal to one.
Kept constant, an imaging apparatus adapted to an output signal of the output signal to the outside. 2. A solid-state imaging device for converting incident light into an electric signal, an amplifying means for amplifying the electric signal, a delay means for delaying an input signal for a predetermined period, and an output signal from the delay means. Multiplying means for multiplying the output signal from the multiplying means and the output signal from the amplifying means and adding the output signal to the delay means; and the level of the output signal from the amplifying means. A level detecting means for detecting the gain of the amplifying means so that the level signal from the level detecting means is equal to the target value, and reducing the target value in accordance with a decrease in the illuminance of the incident light ; And control means for increasing the value to be multiplied by the multiplying means, wherein the output signal level of the adder or the delay means is substantially equal to one.
Kept constant, an imaging apparatus adapted to an output signal of the output signal to the outside. 3. The control means, when the gain of the amplifying means or the illuminance of the incident light is within a predetermined range, the level detecting means.
3. The imaging apparatus according to claim 2, wherein a target value of the level signal and a value to be multiplied by the multiplying means are fixed. 4. The control means, when the gain of the amplification means reaches a predetermined gain value, fixes the gain at the predetermined gain value, and when the value multiplied by the multiplication means reaches a predetermined value. 3. The imaging apparatus according to claim 2, wherein the multiplication value is fixed at the predetermined value, and the fixing of the gain and the fixing of the multiplication value are performed in different ranges of illuminance of incident light.