JPH04330876A - Smear suppression type solid-state image pickup device - Google Patents

Abstract

PURPOSE:To artificially widen the dynamic range of a vertical transfer register in a smear suppression type solid-state image pick-up device to blank-transfer a smear component, output a smear component to the horizontal transfer register for exclusively using the smear charge transfer and subtract the smear component which is the output of a horizontal transfer register for transferring the above-mentioned smear charge from the signal component including the smear component which is the output of the inherent horizontal transfer register for transferring the signal charge. CONSTITUTION:When a signal component including a smear component becomes a high luminance which exceeds the maximum handling charge quantity of a vertical transfer register and overflows, a signal outputted from a horizontal transfer register 6 for transferring a smear charge is added to a signal outputted from a horizontal transfer register 5 for transferring a signal charge. Since an overflowing component overflown and transferred by the horizontal transfer register 6 for transferring the smear charge is added to the signal component, the dynamic range is artificially widened.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a smear suppression type solid-state imaging device, in particular, a vertical transfer register in which a signal component including a smear component and a smear component are separated and vertically transferred, and a horizontal transfer register is used to transfer signal charges. In addition to the horizontal transfer register for signal charge transfer to be horizontally transferred, there is a horizontal transfer register for smear charge transfer, and the horizontal transfer for smear charge transfer is performed from the signal component including the smear component output from the horizontal transfer register for signal charge transfer. The present invention relates to a smear suppressing solid-state imaging device that obtains a signal component by subtracting a smear component output from a register.

0002

2. Description of the Related Art One of the performance requirements for solid-state imaging devices is low smear. and,
In order to reduce smear, there is a smear suppression type fixed image sensor that transfers only the smear component, extracts it separately from the signal, and subtracts the smear component from the signal component that includes the smear component. Such a smear suppression type solid-state imaging device uses a vertical transfer register that divides each bit into two in the transfer direction, so that one side receives the signal component and the smear component, that is, a signal containing the smear component, and the other side receives the smear component. The vertical transfer register separates the signal component including the smear component from the smear component and transfers it vertically, and furthermore, the horizontal transfer register for signal charge transfer horizontally transfers the signal charge. In addition, a horizontal transfer register for smear charge transfer is provided, and a signal is obtained by subtracting the smear component output from the horizontal transfer register for smear charge transfer from the signal component including the smear component output from the horizontal transfer register for signal charge transfer. There is a solid-state imaging device that obtains the components (Japanese Unexamined Patent Application Publication No. 117577/1983, Japanese Patent Application No. 163758/1999).

According to such a smear suppression type solid-state imaging device, the smear component output from the horizontal transfer register for smear charge transfer is subtracted from the signal component including the smear component output from the horizontal transfer register for signal charge transfer. So,
A signal with no smear component or with very little smear component can be obtained. It can be said that it is excellent in that respect.

0004

However, such conventional smear suppression type solid-state imaging devices have a problem in that the amount of subtraction of smear components in areas of the subject that are too bright is excessive. This problem will be explained in detail as follows. The above-mentioned solid-state imaging device that suppresses smear components for overflow components divides each bit of the vertical transfer register into two parts in the transfer direction, and the signal component containing the smear component goes into one part, and the smear component goes into the other part, so that they are mutually separated. Since the transfer is performed while being separated, the charge storage area of each portion into which charges are input is halved by division. Therefore, the maximum amount of signal charges that can be handled by the vertical transfer register, that is, the dynamic range, is halved.

[0005] As a result, when the brightness of the subject becomes high, saturation tends to occur. When it is saturated, excess charge overflows from the part of the vertical transfer register where the signal component including the smear component has entered before and after it, especially to the subsequent part (the part where the smear component has entered) and mixes with the smear component. Then, the charge containing the smear component and the smear suppression is treated as a smear component, and this is subtracted from the signal component including the smear component. Since the amount to be subtracted includes the excess charge, the result of the subtraction is naturally a smaller value than the true signal component. A phenomenon occurs in which the higher the brightness, the lower the signal level.

FIG. 3 is an input/output characteristic diagram showing the relationship between the amount of light and the output signal to explain this phenomenon, and the solid line a shows the relationship between the amount of light and the output signal of the horizontal transfer register for signal charge transfer. , and the solid line b shows the relationship between the light amount and the output for the horizontal transfer register for smear charge transfer. Then, the magnitude of the difference between solid line a and solid line b is output as a signal component, but the reason why the output signal component can be said to be a true signal component is that the signal component including the smear component saturates the vertical transfer register. If the overflow component is exceeded, the overflow component is subtracted from the signal component including the smear component, so the higher the brightness, the lower the level of the output signal component. It turns out that. This is a phenomenon that occurs in black and white images where the brightest area becomes darker than the darker areas. Further, in the case of a color solid-state imaging device, color shift occurs.

[0007] The present invention has been made to solve these problems, and it is intended to apparently widen the dynamic range of a smear-suppressing solid-state imaging device, and to
The purpose is to prevent excessive suppression of smears.

[0008]

[Means for Solving the Problems] The smear suppressing type solid-state imaging device according to claim 1 is characterized in that when the output signal of the horizontal transfer register for signal charge transfer exceeds a predetermined reference value, the output signal of the horizontal transfer register for signal charge transfer is transferred to the horizontal transfer register for signal charge transfer. The present invention is characterized in that a signal obtained by adding the output signals of is output. A smear suppression type solid-state imaging device according to a second aspect of the present invention is the smear suppression type solid-state imaging device according to the first aspect, when the output signal of the horizontal transfer register for signal charge transfer exceeds a predetermined reference value, the signal is used for smear charge transfer. The present invention is characterized in that a signal obtained by subtracting a smear component from a signal obtained by adding the output signals of the horizontal transfer register is output.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The smear suppressing solid-state imaging device of the present invention will be explained in detail below according to the illustrated embodiments. FIG. 1 is a circuit block diagram showing one embodiment of the smear suppression type solid-state imaging device of the present invention. In the drawing, 1 is a vertical transfer register, each bit of which is a signal charge Qsi generated in the light receiving element 2.
The part 3 that receives the signal from g and the smear component Qsme
It is divided in the transfer direction into a portion 4 that secures the data. Therefore, the vertical transfer register 1 receives a signal component Qss (Qss=Qsig +Qsme
) and the smear component Qsm are separated and transferred vertically to the horizontal transfer register.

Reference numeral 5 denotes a horizontal transfer register for signal charge transfer, which is present in all ordinary solid-state imaging devices that do not suppress smear, and transfers a signal component Qss including a smear component. 6 is a horizontal transfer register for smear charge transfer, which transfers only the smear component Qsme, and is provided to suppress the smear component, and is not provided in ordinary solid-state imaging devices. be. 7 is a CDS that receives the output signal of the horizontal transfer register 5 for signal charge transfer;
(correlated double sampling circuit), 8 is a CDS that receives the output circuit of the horizontal transfer register 6 for smear charge transfer. 9 receives the signal output from the CDS 7 at the non-inverting input terminal, receives the signal output from the CDS 8 via the analog switch 10 at the inverting input terminal, and subtracts the smear component from the signal component containing the smear component. This is a differential amplifier that outputs a signal component of .

The analog switch 10 receives the output signal of the CDS8 at one input terminal, and receives the output signal of the CDS8 at the other input terminal.
The inverting amplifier circuit 11 receives a signal obtained by inverting and amplifying the output signal of the differential amplifier 9, and sends the signal specified by the switching control signal to the inverting input terminal of the differential amplifier 9.

Reference numeral 12 denotes a comparison circuit consisting of a differential amplifier, which receives the output signal of the CDS 7 at its non-inverting input terminal and receives the reference voltage Vref at its inverting input terminal. The reference voltage Vr
ef is set to a voltage substantially equal to the output voltage of the CDS 7 when the maximum amount of charge handled by the vertical transfer register 1 is transferred. Then, the comparison circuit 12
When the output signal of S7, that is, the signal component including the smear component, is lower than the reference voltage Vref, the analog switch 1
0 is controlled to select the signal from the CDS 8 and send it to the inverting input terminal of the differential amplifier 9, and when the signal component including the smear component is higher than the reference voltage Vref, the analog switch 10 is controlled to invert the CDS 8. The output signal of the inverting amplifier 11 to be amplified is controlled to a switching state in which it is sent to the inverting input terminal of the differential amplifier 9.

A 1H line memory 13 stores the smear component output from the CDS 8 for 1H (horizontal period). Specifically, the output signal of CDS7 is the reference voltage Vref
When it is lower than the reference voltage Vref, the output signal of the CDS8 is recorded, that is, the smear component is recorded, and when the output signal of the CDS7 is higher than the reference voltage Vref, the recorded signal, more specifically, the last one in the column corresponding to that bit is recorded. CD when the output signal of CDS7 was lower than the reference voltage Vref
The operation is to output the output signal of S8. 14 is an analog switch, which receives the smear component outputted from the 1H line memory 13 at one input terminal, and receives a 0V signal at the other input terminal. The analog switch 14 is controlled by the output signal of the comparison circuit 12, and the signal component including the smear component is the reference voltage Vr.
When the voltage is lower than the reference voltage Vref, a 0V signal is output, and when the signal component including the smear component is higher than the reference voltage Vref, the smear component from the 1H line memory 13 is output.

A differential amplifier 15 receives the output signal of the differential amplifier 9 at its non-inverting input terminal, receives the signal from the analog switch 14 at its inverting input terminal, and sends its output to the signal processing circuit 16.

Next, the operation will be explained. First, the CD
When the signal output from S7, that is, the signal component including a smear component, is lower than the reference voltage Vref, the smear component from CDS8 is input to the inverting input terminal of differential amplifier 9 via analog switch 10, and this It is subtracted from the signal component including the smear component output from the CDS 7. That is, smear components are removed. Then, the signal component from which the smear component has been removed is input from the differential amplifier 9 to the signal processing circuit 16 via the differential amplifier 15. At this time, since a 0V signal is output from the analog switch 14, the differential amplifier 15 outputs the signal output from the differential amplifier 9, which is received at its non-inverting input terminal, as it is without subtracting it.

Next, when the signal output from the CDS 7, ie, the signal component including the smear component, is higher than the reference voltage Vref, the analog switch 9 is switched to select the output of the inverting amplifier circuit 11. Therefore, the inverted amplified signal of the smear component is input to the inverting input terminal of the differential amplifier 9, and as a result, the differential amplifier 9 outputs the CDS7 and CDS7.
A signal obtained by adding the output signals of S8 will be output.

Therefore, the overflow component that overflows from the signal charge storage section of the vertical transfer register 1 to the smear component storage section when the brightness becomes high is not subtracted from the signal component including the smear component, but is added to the signal component, and the addition The signal obtained can be used as a signal charge, and the overflow component can be incorporated into the signal component and output without ignoring it. Therefore, the relationship between the light intensity of the smear suppression type solid-state imaging device of FIG. 1 and the output signal of the smear suppression circuit is approximately as shown by the solid line in FIG. That is, even if the maximum handling charge amount is the same, the dynamic range is expanded by the action of the smear suppression circuit, and it is possible to prevent image quality from deteriorating due to excessive smear suppression.

Incidentally, when the signal component including the smear component is higher than the reference voltage Vref as described above, the analog switch 14 receives the output signal from the 1H line memory 13 and inputs it to the inverting input terminal of the differential amplifier 15. It will be in the switching state. Then, the smear component output from this 1H line memory 13 is subtracted from the output signal of the amplifier 9. This is done because the output signal of CDS8, which is added to the signal component including the smear component that is the output signal of CDS7, includes not only the overflow component but also the smear component. This is in order to further improve the output characteristics of the amount of light by removing this, so to speak, to reduce signal errors.

Note that the 1H line memory 8 becomes inaccurate if it transfers a smear component that includes an overflow component, so it operates as follows to avoid transferring a smear component that includes an overflow component. There is. That is, when the output signal of the CDS 7 is lower than the reference voltage Vref, the output signal of the CDS 8, that is, the smear component is recorded. Then, the output signal of CDS7 is the reference voltage Vre.
When it is higher than the reference voltage Vref, the recorded signal, more specifically, the output signal of the CDS 8 when the last output signal of the CDS 7 was lower than the reference voltage Vref in the column corresponding to that bit is output.

According to such a smear suppressing type solid-state imaging device, when the signal charge, more precisely, the signal component including the smear component, is larger than the maximum charge amount handled by the vertical transfer register and therefore overflows, the signal charge is overflowed and the smear is generated. Since the signal captured in the component is added to the signal component including the smear component, the overflow component can be substantially captured as a part of the signal component, and the dynamic range can be widened. In addition, it is possible to prevent excessive smear suppression, and furthermore, it is possible to prevent the image quality from deteriorating due to the excessive smear suppression.

After adding the overflow component including the smear component to the signal component including the smear component, 1H
Since the smear component is subtracted by the functions of the line memory 13 and the differential amplifier 15, it is possible to prevent the smear component in addition to the overflow component from being added to the signal component including the smear component, and this prevents the smear component from being added to the signal component including the smear component. Errors can be reduced.

Note that it is not essential to provide the 1H line memory 13, analog switch 14, and differential amplifier 15 to eliminate errors due to smear components during high brightness. Furthermore, it goes without saying that the smear suppression circuit may be provided outside or inside the solid-state image sensor. As described above, the present invention can be implemented in various ways.

[0023]

In the smear suppression type solid-state imaging device according to claim 1, the vertical transfer register separates the signal component including the smear component from the smear component for vertical transfer, and the horizontal transfer register transfers the signal charge horizontally. In addition to the horizontal transfer register for signal charge transfer, a horizontal transfer register for smear charge transfer is provided, and the signal component including the smear component output from the horizontal transfer register for signal charge transfer is output from the horizontal transfer register for transfer of smear charge. In a smear suppressing solid-state imaging device that obtains a signal component by subtracting the smear component, it is determined whether the signal component including the smear component output from the horizontal transfer register for signal charge transfer exceeds a predetermined reference value. and outputs the signal component obtained by the subtraction only when the signal component including the smear component does not exceed the reference value according to the determination result of the determination means, and the signal component including the smear component does not exceed the reference value. When the value is exceeded, the signal output from the horizontal transfer register for signal charge transfer is added to the signal output from the horizontal transfer register for signal charge transfer, and the result is output. . Therefore, according to the smear suppression type solid-state imaging device of claim 1, when the signal component including the smear component exceeds the maximum handling charge amount of the vertical transfer register and the overflow component is incorporated into the smear component, the signal component includes the smear component. Since the overflow component is added to the signal component along with the smear component, the value incorporating the overflow component can be used as the signal component, making it possible to substantially widen the dynamic range and preventing excessive smear suppression at high brightness. In addition, it is possible to prevent image quality from deteriorating due to excessive smear suppression. A smear suppressing type solid-state imaging device according to a second aspect of the present invention is a smear suppressing type solid-state imaging device according to a first aspect, in which when a signal component including a smear component exceeds the reference value, the signal charge is output from the horizontal transfer register for signal charge transfer. The present invention is characterized in that the smear component is subtracted from the signal obtained by adding the signal output from the horizontal transfer register for smear charge transfer to the signal output from the horizontal transfer register for smear charge transfer. Therefore, according to the smear suppression type solid-state imaging device of claim 2, since the smear component is subtracted from the signal obtained by adding the overflow component including the smear component to the signal component including the smear component at high brightness, the overflow component is the smear component. This prevents the smear component from being added to the signal component containing the smear component, thereby further reducing errors during high brightness.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing one embodiment of the smear suppression type solid-state imaging device of the present invention.

FIG. 2 is an input/output characteristic diagram of the embodiment shown in FIG. 1;

FIG. 3 is an input/output characteristic diagram of a conventional smear suppression type solid-state imaging device for explaining the problem to be solved by the invention.

[Explanation of symbols]

1 Vertical transfer register 5 Horizontal transfer register for signal charge transfer 6 Horizontal transfer register for smear charge transfer 9 Differential amplifier 12 Judgment means

Claims (1)

[Claims] 1. A vertical transfer register separates a signal component including a smear component from a smear component for vertical transfer, and the horizontal transfer register serves as a horizontal transfer register for signal charge transfer that horizontally transfers signal charges. A horizontal transfer register for charge transfer is provided, and a signal component is obtained by subtracting a smear component output from the horizontal transfer register for smear charge transfer from a signal component including a smear component output from the horizontal transfer register for signal charge transfer. The smear suppression type solid-state imaging device includes a determination means for determining whether a signal component including a smear component output from the horizontal transfer register for signal charge transfer exceeds a predetermined reference value, and a determination result of the determination means is provided. According to A smear-suppressing solid-state imaging device, characterized in that the signal output from the horizontal transfer register for smear charge transfer is added to the signal output from the transfer register and output.Claim 2: Contains a smear component. When the signal component exceeds the above reference value, the smear component is subtracted from the signal obtained by adding the signal output from the horizontal transfer register for signal charge transfer to the signal output from the horizontal transfer register for smear charge transfer. Claim 1 characterized in that the output is performed by
Smear suppression type solid-state imaging device described