JPH0332284A - Signal processing method for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To use a solid-state image pickup device to a place, where the quantity of incident light is small, by separately reading an output voltage, for which a dark time output is superimposed to a signal voltage, and the dark time output of an electric charge accumulating part and subtracting the latter from the former in the internal part of a microcomputer. CONSTITUTION:A first control gate 6 is provided to transfer a signal charge to electric charge accumulating parts 5a-5n and a second control gate 10 is provided to directly discharge the signal charge to electric charge exhaustion drain parts 9a-9n in each photosensitive picture element of a solid-state image pickup device 1. In the first signal reading, a voltage more than a threshold voltage is applied to the first control gate 6 and the gate 6 is set in a conductive state. Then, the signal voltage and dark time output are read. In the second signal reading, the voltage more than the threshold voltage is applied to the second control gate 10 and the gate 10 is set in the conductive state. Then, the dark time output voltages of the electric charge accumulating parts 5a-5n are read. Thus, an object with illuminance lower than the conventional illuminance can be picked up on the solid-state image pickup device 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is a system for all C devices using a solid-state imaging device, -1
For example, it relates to a signal processing method K for a solid-state imaging device of an automatic focusing device.

[Conventional technology]

Figure 5 is an example of a conventional solid-state camera autofocus device (outline of the device, signal processing unit, and operations department +11j Al1).
This is an explanatory diagram showing the dust sequence of
(2) is a signal processing unit that uses the output of the solid-state camera 1 (Rt1) as human power; (3) is an arithmetic processing unit that receives the 1b power of the signal processing unit (2) as input; ! Device (1)
is constructed as follows. (4a) to (4n) are a plurality of pixels arranged on a substrate that generate photocharges according to incident photoacid, and (5a) to (5n) are signals generated by pixels (4a) to (4n). A charge storage unit that stores charges; (6) a control gate that controls the signal charges of a plurality of pixels (4a) to (4n) to flow into the corresponding charge storage units (5a) to (5n); (7a) to (7n) are charge storage parts (5a)
a charge discharge drain section for discharging signal charges of ~(5n);
(8a) to (8n) are charge discharge drain parts (7a) to (7
n) a gate for discharging charges to control the inflow into ti;
ll is a transfer unit that transfers signal charges accumulated for a certain period in charge accumulation units (5a) to (5n), (1z is a charge accumulation unit (
Transfer gates that control the flow of signal charges 5a) to (5n) into the transfer section [111;
11) This is an output unit that converts the signal charge transferred from the output unit into a voltage signal. The signal processing section (2) has a solid-state camera mounting (1
) is input, (input is a clamp circuit that sets the DC voltage to a certain DC voltage when there is no signal of the output signal, (10 is a sample and hold circuit, (10 is an A/D conversion circuit, and (10 is an A/D conversion circuit. 3) takes the output of the signal processing unit (2) as input,
(One is the microcomputer part, (1 mark is the memory part. Figure 6 shows the Vl-
A cross-sectional view taken along the W line is shown below, and the operation will be described next.

Signal charges generated in the photosensitive pixels (4a) to (4n) are accumulated in charge storage sections (5a) to (5n) corresponding to each pixel.

A direct current voltage higher than the threshold voltage is applied to the control gate (6). Charge storage section (5a) to (5n) The charge storage section in which K is accumulated is determined by the accumulation time Tint in the timing chart shown in Fig. 7, the incident photoacid, and the dark current.When there is a large amount of incident photoacid, the accumulation time Tint is A monitoring means (not shown in FIG. 5) is used to adjust the accumulation time T so that the accumulation time T is short and when the amount of incident photoacid is small, the accumulation time T is lengthened to provide a wide dynamic range t% with respect to the incident photoacid.
Clean up int. Charge accumulation g(
The signal charge transfer section (5a) to (5n)
11) is completed, and in the period tli, each charge storage unit (
The transfer of the i-word electric music stored in 5a) to (5n) is started. The signal charge to be transferred is converted into a voltage signal by the output section (131) provided at the end of the transfer section tll), and the signal charge stored in each charge storage section (5a) to (5n) is sequentially transferred to the output section (131). Convert to signal voltage (hereinafter,
The 1b output voltage of the output section X13) is called the time-series output voltage)
. This time series output voltage is passed through a clamp circuit (14) and a sample hold circuit (151) in the signal processing section (2) to C1.
After passing through the so-called H] Seki 2@sample times + 13 (SDA), it is A/D converted and then sent to the microcomputer section (1) of the arithmetic processing section (3).
The data is input to the storage unit 1181 and stored in the VC-Jibo storage unit.

After repeating the above signal readout several times, the microcomputer unit (17) calculates the average value of the several readouts to obtain the nine-eye relative distribution of the photosensitive pixels (4a) to (4n).

[Problem to be Solved by the Invention 1 Figure 8 (at) shows a typical time-series signal voltage. When the amount of incident photoacid is small, +'+i Tint must be lengthened during accumulation, and as a result, the photoacid The signal voltage corresponding to the dark current has the same level of dark output as the signal voltage corresponding to the dark current. As shown in No. 81'Hbl, the dark output is
1.The light of the photosensitive pixel is 1 because the output trj is fluctuating.
+ It is no longer compatible with cloth. In addition, most of the dark output at this time is the dark output generated in the charge storage section.The conventional solid-state camera is not configured to compensate for the dark output with the signal processing method described in section 8. , When there is little incident photoacid, that is, when it is dark, the S/N ratio is poor when photographing the subject on a solid + @ acid device, so it is impossible to detect the exact light distribution of the subject. There was a problem prefecture.

This invention was made in order to eliminate the above-mentioned gap, and it is possible to change the S state north at the same time as before, and also to reduce the amount of incident photoacid to a place where there is less incident photoacid than before. The purpose of this invention is to improve a signal processing method for a body image pickup device that can use body image sensors.

[Means for solving problems]

Solid-state imaging I3 according to this invention! The signal processing section of the device includes a first control gate that transfers the signal charge to the charge storage section for each photosensitive pixel of the solid-state sensor, and a second gate that directly discharges the signal charge to the charge discharge drain section. 2 control gates are provided, and when reading the 1st and 4th A word, a voltage higher than the threshold voltage is applied to the 1st 1st and 1st raised gates to make them conductive, and the signal voltage and dark output continue. In the second signal readout, a voltage higher than the threshold voltage is applied to the second suppressing gate so that the output voltage during the dark period of the storage unit increases by 1.

[Effect]

In the signal processing of the solid-state imaging device according to the present invention, the output voltage obtained by adding the dark output to the signal voltage and the dark output of the charge storage section are read out separately, and the latter is subtracted from the former within the microcomputer. By doing so, a signal output with reduced dark time output is obtained.

[Example] One embodiment of the present invention-1 will be explained with reference to the drawings. In FIG. 1, (9a) to (9n) are photosensitive pixels (4a)
~ [4n) a second charge discharging drain section provided next to the
Oω is a second control gate that restricts the inflow of signal charges generated in the photosensitive pixels (4a) to (4n) into the second charge discharge drain section; 9
The configuration is the same as the conventional one except for the provision of the second control gate (10) and the second control gate (10). Tatashi, (6)
The control gates are the first control gates, (7a) to (7n)
The charge discharging drain section is the first charge discharging drain section. Figure 2 is a cross-sectional view taken along the [1-II line] of Figure 1 formed in the P-type amended layer in the n-type substrate, and Figure 3 is a cross-sectional view of the
The figure shows a timing chart of the clock voltage manually applied to each gate to be omitted. In the figure, (al is the transfer unit clock voltage input to the transfer unit ), tc) is the clock voltage manually input to the second control gate (101), (di is the clear gate clock manually input to the clear gates (8a) to (8n), and (e) is the transfer gate clock voltage input manually to the second control gate (101). In the transfer gate clock input to the gate (12), (fl indicates each timing.

Next, the operation will be explained. During period C of t3 of the first signal readout shown in the timing chart of FIG. Since four voltages above the threshold voltage are applied, i! Furthermore, the storage section (5a) ~
A signal charge Qsig+fil as shown in the following equation (1) is accumulated in the i-th cell of (5n).

Qsig +Iil = Qphoto d it
+ Qdarkp Dlfil + Qdarkstl
(i) -il) Here, Qphoto+(il is the optical signal charge generated in response to the incident light at the first photosensitive pixel (41), Qdarkp D, Ii) is the photosensitive pixel (41) at the first photosensitive pixel (41), ) is the dark output charge due to the dark current generated regardless of the incident light, and Qdarkst + (i) is the dark output charge due to the dark current generated regardless of the incident light at the i-th charge storage section (51). . Each charge storage section (5a) ~
The charge Qsig+fil accumulated at (5n) is transferred at the transfer section full and converted into a voltage signal at the output section (131).

The signal voltage Vsigt(il
is Vsig mountain 1 = Vphotottil + Vdar
kpD1til+ Vdarkstl(il ・---
It will be i21. Vsigt(i), Vphotot
[il t VdarkpDltil, Vdark
stt(il is Qsigt(il + Qphotol
til, QdarkpD mountain 1, Qdarkst
It is a voltage proportional to l (il. Figure 4 shows a part of the waveform of the voltage FJF at the output of the output section (131) and (7) Vsigt (il, Vphotol).
? tl, ■arkpD, (i) +■arkst+fi
). As shown in this figure, the dark output voltage ■ar generated in each photosensitive pixel (4a) to (4n)
The dark output voltage and voltage Vd generated in each charge storage section (5a) to (5n) from kpp1fil (i = a to n)
arkstt(il (i=a-n) is generally at a sufficient level. The signal voltage Vsigt(il is the signal voltage Vsigt(il) corresponding to the accumulated charge of each charge storage section (5a) to (5n) ), and the correlation square sampling circuit and A/
After being converted into D and input to the microcomputer section (closed) of the arithmetic processing section (3), it is held at -1,1 storage section 0 mark. Fig. 2 ff
During period 17 of the second signal readout shown in the + timing chart, a voltage equal to or higher than the threshold voltage is applied to the first control gate (6), and a voltage equal to or higher than the threshold voltage is applied to the second control gate (1ω). Since a voltage higher than the value voltage is applied, the optical signal charge Qphoto generated in each photosensitive pixel portion (4a) to (4n)
o2(il and dark output charge QdarkpD2fil are discharged to the second charge discharging drain parts (9a) to (9n). As a result, i of the charge storage parts (5a) to (5n)
The signal charge Qsig as shown in the following equation (3) is
2(il is accumulated.

Qsig2fi) = Qdarkst2(il
-(31 Here, Qdarkst2(il is the il-th charge, 4'!: is the dark output charge due to the dark current generated in the product part (51) regardless of the incident light. This signal charge Qs
ig2fil is transferred by the transfer unit (11) and output to the output unit (1
3), the signal voltage Vsig2+il corresponding to Qsig2fil is converted to Vsig2(il
= Vdarkst2fil - (4)
becomes. FIG. 4(b) shows a part of the voltage waveform at the output of the 1n power section (131) and Vsig2(it,
Vdarkst2(it shows a typical ratio of Vdarkst2(it). However, the accumulation time Tin of periods t3 and t7 of
t+ and Tint2 are Tintl = Tint2−
- t5), so VdarksT, fil= Vdarkst2fi)
(i=a−n) −=t61. The signal voltage Vsig2(i) shown by the simple equation (4) is
After passing through the phase-to-phase square sampling circuit and the A/D conversion circuit, it is input to the microcomputer section t17 of the arithmetic processing section (3) and is inputted to the above-mentioned once-input section (the first The signal voltage Vsigz(it) for the second signal readout is subtracted from the signal voltage Vsig+(il for the signal readout) in the microcomputer unit (I7), and as a result,
Dark output voltage ■a in charge storage sections (5a) to (5n)
rksT1fit (= Vdarks・r2(i))
The signal voltage Vsi as shown in the following equation (7) after removing
g is calculated inside the microcomputer (17).

Vsig = Vsig+ -Vsig2 = Vph
otol (il+■arkpo, (il +Vdar
ksT, fil −VdarksT2fit =Vp
hot+fil + VdarkpD, fit -f
7) Signal output Vsig + (i) voltage Vphoto peak), VdarkpD, fit shown in the previous formula (2)
, Mt. Vdarkst), IJ, 11th station is shown in Figure 4 fc
l, and with the above signal processing, we get
The signal output of the previous equation (7) is as shown in Figure 4 fd),
For the signal output Vsig(nl), one part of noise is reduced.

In addition, in the above embodiment, when the first signal 1 is output, the first signal is
Set the control gate (6) of
In the second signal detection, the case where the first control gate (6) was set to the threshold voltage or higher and the second control gate (tld) was set to the threshold voltage or higher was shown. At the second traffic light, even if I reversed the direction, the light still wouldn't turn on, and again,
There is no problem even if the first and second signal readings are repeated multiple times.

〔Effect of the invention〕

As described above, according to the present invention, since the band (Vdarf<st fn) generated in the charge storage section can be canceled for each lilI element from the signal output,
The S/N ratio is better than before, and as a result, it is possible to capture objects with lower illuminance on the solid-state imaging device than before, and since the noise component is canceled for each pixel, it is possible to capture images with less contrast. Even when photographing subjects in low light, images with less noise than before can be reproduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an outline of a wide body imaging device according to an embodiment of the present invention and connections between a signal processing section and an arithmetic processing section, and FIG. 2 is an n-type board in the II-n green shown in FIG. 3 is a timing chart of the signal input to the solid-state imaging bag d section of FIG. 1,
FIG. 4(a) is a waveform diagram output from the output section at timing t4LU of FIG. 3(f).
The waveform diagram output from the output section is shown in the timing chart of
Figure fc) is a table showing the component ratio of the signal output of Figure fa),
Figure (dl is the signal output after canceling the maintenance component [
Figure 5 is an explanatory diagram showing the outline of the conventional solid-state imaging system and the connections between the signal processing section and the arithmetic processing section. For example, FIG. 7 is a timing chart of each signal manually input to the solid-state imaging device of FIG. 5,
Fig. 8 fa) is a signal waveform diagram output from the output section shown in Fig. 5, and Fig. fb) is a waveform diagram showing signal components of the signal waveform indicated by [](at. is a solid-state imaging device, (2) is a signal processing Ji
I! (3) is an arithmetic processing unit, (4a) to (4n) are photosensitive pixel units, (5a) to (5n) are electric charge storage units, (6) is a first control date, (7a) to ( 7n) is the first charge discharging drain part, (9a) to (9n) are the second charge discharging drain parts, (I(T) is the second control gate, (11)
) is the transfer section, (13 is the output section, (17) is the microcomputer section,
(18) indicates a storage section. In addition, in the figures, the same reference numerals indicate the same parts or (I).

Claims (1)

[Claims] a photosensitive pixel section that performs photoelectric conversion in each of the plurality of pixels arranged on the substrate and generates photocharges according to the amount of incident light; a charge storage section that temporarily accumulates signal charges generated in the photosensitive pixel section; a first control gate that controls the inflow of signal charges from the photosensitive pixel section to the charge storage section; a first charge discharge drain section that discharges the signal charges stored in the charge storage section; a second charge discharge drain section that discharges generated signal charges; a second control gate that controls the inflow of signal charges from the photosensitive pixel section to the second charge discharge drain section; A solid-state imaging device including a transfer section that transfers signal charges accumulated over a period of time, an output section that converts the signal charges transferred by the transfer section into a voltage signal, and a signal processing section that processes the signal of the output section. In a signal processing method for a solid-state imaging device, the signal processing method for a solid-state imaging device includes a microcomputer unit that performs arithmetic processing on a time-series signal according to the amount of incident light of the signal processing unit, and a storage unit that stores the result of the arithmetic processing. When performing readout, a first control voltage equal to or higher than a threshold voltage that causes charges to flow from the photosensitive pixel section to the charge storage section is applied to the first control gate during the first readout, and the second control voltage is applied to the first control gate. A signal processing method for a solid-state imaging device, characterized in that a second control voltage is sometimes applied to a second control gate, and the first and second read operations are repeated several times.