JPS60167580A - Solid-state image pick up device - Google Patents

Abstract

PURPOSE:To improve SN ratio at the time of image pickup under low irradiation by constituting a single horizontal scan line of two row light emitting diodes at the time of image pickup under sufficient irradiation when signals are read from the photodiodes arranged in a array form, and constituting the horizontal scan line of a single row photodiode under low irradiation. CONSTITUTION:A MOS solid-state image pickup element uses a color filter arrangement as shown in fig. gate circuits 121, 122,... are inserted between an interrace circuit 6 and output lines 71, 72,.... When an on signal is added to a control terminal 151 and an off signal to a control terminal 152 at an odd field, for example, during the first horizontal scan period, even if output pulses are added from the interrace circuit 6 to the circuits 121 and 122 from the output race circuit 6 to the circuits 121 and 122, the output pulses are transferred only to the output line 71 and the only photodiode of the first row is transferred to vertical signal lines 32, 34, 36,..., by which an interrace operation of every one odd row jump over is made possible in the first field and equally every one even row jumover in the second field. Adversely, the conventional two rows simultaneous read is made possible by a control signal applied to the control terminals 151 and 152.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a solid-state imaging device, and particularly to noise improvement of a solid-state imaging device.

[Background of the Invention] Recently, solid-state imaging devices have come to be used as photoelectric conversion devices in imaging devices that convert the subject into an electrical signal due to advances in semiconductor integrated circuit technology.

However, there were some points to be improved regarding the sensitivity of photoelectric conversion. That is, the signal-to-noise ratio during imaging under low illuminance is improved.

First, the operating principle and signal processing method of a solid-state image sensor will be explained using an MO8 type solid-state image sensor as an example.

In the MO8 type solid-state image pickup device shown in FIG.

First, in the odd field, the output edges 71 and 72 r 7g
, , 7, pulses are sequentially sent from the interlacing circuit 6. As a result, for example, in the first horizontal scanning period, 3- are all turned on, so the original diodes 11-1 and l'+-+ r It-g and l/, - snow, 11-3 of the M1 row and 1't-s l... are respectively transmitted to the vertical signal line 33 r 34 + 36 +
..., and the original diodes in the second row are 1 to 1 and 1' to 1 to 2 and 1' to 2, 1 to 3, and 11-3...
The optical signals of ... are respectively transmitted to the vertical signal lines 3+, 3a,
3g.

It will be moved to... In addition, one pixel is composed of valley pairs such as the original diode 11-1, I'l-1111-2, I'S-1, etc., and the signal of each pair is transferred to the vertical signal scarlet and mixed at the friend point. This results in a signal for one pixel.

On the other hand, during the horizontal scanning period, the output line 9. from the horizontal shift register 8. ．． 9. ．． 9. The output pulses sequentially sent to ... are simultaneously sent to three sets of horizontal switch transistors (1
01, IOa, 10g), (104, 10s,
l0a).

(10?, IQs, 109), .
output to the outside of the element.

Next, in an even field, the combination of two output lines of the interlacing circuit 6 that can simultaneously obtain output pulses from the vertical shift register 4-→ is shifted. When the output pulses sequentially sent to the output lines 51., 52.5s, ..., 5+n are applied to the interlace circuit 6, the output lines 72 and 7B, 74 and 7s, ..., 78□- 2
and 7t-1 at the same time) (Rus is sent to the two valley bears @ of 7t-1 at the same time) (Rus is sent. For example, during the first horizontal scanning period, the photodiodes 1!-11 and I's of the second row
-Ir13-2 and I's-t*12-@ and l'
2-3. The optical signals of... are respectively transmitted to the vertical signal lines 31.
Moved to 3g, 3s,..., #! Third row original diode 13-1 and t's-t・13-2 and l/3
− heat °°°° optical signals are vertical signals m h , respectively;
34 r 3a,... Then, they are connected to the signal output lines 11'l,
IIs, output from IIs to the outside of the element.

By the operation described above, the signal output 1+11s*11
The signal obtained from m is shifted up or down by one row of the original diode array from field to field, resulting in a catastrophic scan line interlacing behavior.

According to this type of interlace operation, the optical signals obtained from all photodiodes are output from the signal output terminal for each field, so when the subject moves, the length of the afterimage remaining on the photodiodes changes. This becomes a parable that corresponds to the distance, and it is possible to prevent visually disturbing afterimages. It is also advantageous in colorization, which will be described below.

In the image sensor shown in FIG. 1, three horizontal switch transistors 10 are turned on at the same time. Therefore, the spatial positional relationship of each pixel and the signal output terminal 111, IIs'
, IIs. However, this problem can be solved by returning the signals 'eM' from the signal output terminals 112 and 113 to the original spatial relationship.

In order to obtain a color video signal from the Δ408 type solid-state image sensor shown in FIG. 1, it is necessary to arrange a color filter for color separation f corresponding to each pixel. FIG. 2 shows the arrangement of color filters. The color filter is white (W), which transmits all color light.
Red light f: consists of three colors: cyan (Cy), which does not transmit blue light, and yellow (Ye), which does not transmit blue light.

Each color filter shown in FIG. 2 has W(1-1) in the photodiode l 1-1 and I' 1-1 shown in FIG. 11 and 111-, and cy(+.2) are arranged in correspondence with each other. As a result, a cyan (Cy) signal is obtained from the signal output 1m I 1 t, a white (w'N!i) signal is obtained from the signal output terminal +12, and a yellow (Ye) signal is obtained from the signal output terminal 113. Color video signal To configure this, luminance signals (Y, red signal (R), and blue signal (B) are required).

Here, an example of an MO8 type misimage device is shown below.

The sensitivity ratio of each party of G and B is R:G:B:4:5:1, and the subtracted signals of Cy, Ye, and W are expressed as follows: Y=W+Ye+Cy (11 As is) If used as a luminance signal, a value of Y=0.32R+0.6G+0.08B 7- can be obtained, which is relatively close to Y=0.3R+0.59G+0.11B of the NTSC system.

10,000, red light (R) and green light (B) can be obtained by the following formula.

R=w-cy (21 B=W-Ye (31) The resolution in a single-chip color solid-state image sensor that obtains a color signal using a single solid-state image sensor is limited by the repetition frequency of the color filter arrangement.

When a signal for one horizontal scan fa is composed of signals from two rows of photodiodes arrayed in a vc array, when the color filter arrangement w1 shown in FIG. The resolution is higher than that of 2 screen cycles. Furthermore, the refined signal processing in which the W, Cy, and Ye signals are obtained from independent signal output terminals is greatly simplified.

8- It is also advantageous, roughly speaking, regarding the afterimage properties, since all photodiodes are read out every field period.

However, reading out all the signals of two rows of photodiodes arranged in a play pattern at the same time is advantageous in terms of afterimages and resolution, but it is difficult to improve the signal-to-noise ratio due to lack of sensitivity when imaging under low illumination. There was room.

[Purpose of the invention]

The objective is to provide a solid-state imaging device with an improved two-to-one signal-to-noise ratio when capturing images under low illuminance.

[Summary of the invention]

In order to achieve such an object, the present invention provides a method for reading out signals from photodiodes arranged in an array.
During normal imaging under sufficient illuminance, photodiode 2
By constructing one horizontal scanning line with one row of photodiodes and one horizontal scanning line with one row of photodiodes when imaging under low illumination, the signal-to-noise ratio during imaging under low illumination is improved. It is something.

[Embodiments of the invention]

Random noise I generated in the solid-state image sensor shown in Figure 1
The nth number can be expressed by the following equation.

I"ni == 4-n-k-T-Cv-Lp・Δf
(5) Here, n: Number of signal output lines: Boltzmann constant T: Absolute temperature C7: Vertical signal a capacity O f cp: Horizontal shift register driving frequency Δf: Signal frequency band.

During imaging under low illumination, if you read out every other row of photodiodes instead of reading out two rows of photodiodes at the same time, as is clear from the color filter arrangement shown in Figure 2, the same color will be displayed. A signal is obtained every two clocks. In other words, this corresponds to the value of f/p in the +51 formula being halved.

Further, along with this, 8f is also halved, and the random noise I'llll when reading out one row from the other is as follows.

Preamplifier noise is a problem in MO8 type solid-state imaging devices. FIG. 3 shows an equivalent circuit of the preamplifier and solid-state image sensor. C0 is the output valley of the solid-state image sensor,
Ct is the input capacity of the junction FET'13 in the first stage of the preamplifier and the floating silkworm, It・, is the input capacity of the junction FET '13, etc.
I noise resistance value, RL is feedback resistance value.

14 is an amplifier called Cain G (G, >> 1).

Random noise InA generated in this preamplifier can be expressed by the following equation.

1/1 p? As mentioned in I, when reading every other row of photodiodes, Δ
f is half of that when two rows of original diodes are read out simultaneously. Furthermore, the repetition frequency of the color signal can also be determined. So get a glance.

From the above, the total noise N and 1 when reading two lines simultaneously
The overall noise N/ during line skip reading has the following relationship.

N2 = I"11. + I2areA (9) N" =
I4a +I''nA Therefore, it becomes possible to significantly reduce noise during one-line interlaced reading.

Next, embodiments of the present invention will be described in detail using the drawings.

Embodiment I FIG. 4 shows the MOB type solid-state imaging device used in this embodiment. The difference from the MO8 type imaging sensor shown in FIG. 1 is the interlacing circuit 6 and the output line 71.7x-7s.

-12=..., gate circuits 12t, 122. between 72m.
..., insert 12g□ and say Friend. The control inputs of the gate circuit are each connected to separate control terminals 15K and 15K. Here, an on signal t- is applied to the control terminal 151 in the odd field, and the control terminal 15! If an off signal is added to the line 71, for example, even if an output pulse is applied from the interlacing circuit 6 to the gate circuits 121 and 12 during the first horizontal scanning period, the output pulse will be transmitted only to the output line 71. As a result, only the signals from the photodiodes in the first row are transferred to the vertical signal lines 3* r 3a r 3s, . . . . This results in an odd number of rows in the first field.

In the second field, an interlacing operation in which even-numbered lines are skipped by one line is possible. It goes without saying that conversely, the conventional two-row simultaneous readout is also possible by controlling the control signals applied to the control terminals 151, 151.

The color filter arrangement shown in FIG. 2 is used for the MO8 type solid-state image pickup device shown in FIG. 4 as well, as in the case of the single-image device shown in FIG.

FIG. 5 shows an embodiment for processing the signals obtained from the 4M MO8 type solid state image element 16. In FIG.

First, the signal obtained from the image carrier 16 is 1reamplified 17+
, 171 , amplified at 17g. Thereafter, as described above, since the timing and spatial positional relationship of the video signals are different, this difference is corrected by the delay circuits 181 and 182. Addition circuit 19 and subtraction circuit 20! and 20
2 is for performing all calculations of equations +11, (2) 2, and (3), respectively. The switch circuit 21 is used to switch between the low-pass filter 22+ and the 222-karat gold during normal imaging under sufficient illumination and during continuous imaging under low II 4 degrees. Note that the low-pass filter 222
is 22. The frequency band is about half of that of 24 is 2
This is a circuit that determines whether to read out rows simultaneously or to read out one row at a time, and it can be determined by a manual switch or by automatically determining the illumination conditions by using a photodiode or the like. 23 are control terminals 131 and I3! according to the judgment of the reading method determining circuit 24. This circuit generates control signals necessary for simultaneous reading of two rows or interlaced reading of one row. Note that the switch circuit 21 also has 24
It operates by the signal VC from.

can be obtained.

Embodiment 2 Another embodiment is shown in FIG. The difference from the embodiment shown in FIG. 5 is the preamplifier 17+ and the delay circuit 181°! This is because switch circuits 21+, 212, and 21a are provided after 82. Under low illuminance, by reading out one line of the original diode, the noise during the achromatic period can be cut by the switch circuits 211 and 2111213, so that the ratio shown in equation (11) can be improved. was completed. Note that 25 is a switch circuit 211.2 Is, 2 according to the judgment of the reading method determining circuit 24.
This is a switching pulse generation circuit that switches Is.

Embodiment 3-15 = FIG. 7 shows an embodiment of a two-wire output type BJ 08 image sensor image sensor 26 having an output terminal IIs and 11 layers. The embodiment shown in FIG. 4 is a solid-state color image sensor, but the embodiment shown in FIG. 7 is a monochrome image sensor without a color filter. FIG. 8 shows the signal processing circuit in this device. Happy 5
The only difference from the figure is that since it is a monochrome element, there is no need to separate the red signal (R) and the green signal (B), so the explanation will be omitted.

〔Effect of the invention〕

As described above, the present invention can always obtain high-quality video signals with high sensitivity and low noise by switching the readout method from the photodiode array depending on the illumination conditions.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the signal readout method of the image sensor of the MOS image pickup device, FIG. 2 is a diagram showing an embodiment of the color filter arrangement used in one embodiment of the present invention, and FIG. The circuit diagrams of the preamplifier used in one embodiment of the invention are shown in Figures 4 and 7, and other embodiments of the present invention are shown in Figures 5, 46, and 8.
What about signal processing according to the present invention? Illustrated in the diagram.

Claims (1)

[Claims] (1) In a solid-state imaging device having mourning photosensitive pixels t- arranged in an array in two dimensions in the horizontal and vertical directions, the repetition period in the horizontal direction of the photosensitive pixel array is constant;
In odd-numbered rows and even-numbered rows, the arrangement of photosensitive pixels is shifted by half a cycle, and (al) two adjacent photosensitive pixels are arranged.
(b) The row of photosensitive pixels! - A solid-state imaging device configured to be switched between reading out every other row and configuring a heavy water half-scanning line signal, and characterized in that: 2. When imaging under sufficient illuminance, two adjacent rows of the photosensitive pixels are simultaneously read out to form the I horizontal scanning line signal; when imaging is performed under relatively low illuminance, the rows of the photosensitive pixels are read out simultaneously. 2. The solid-state imaging device according to claim 1, wherein the I horizontal scanning line signal is constructed by reading out every other row. 3. Read out two adjacent rows of the photosensitive pixels at the same time!
When configuring horizontal scanning line signals, the repetition period in the horizontal direction of the solid-state imaging device array according to claim 2 of the preceding claim is constant, but the array of photosensitive pixels is different between odd and even rows. Three types of color filters, ie, a first color filter, a second color filter, and a third color filter, are arranged in a staggered manner by half a period, and in front of the photosensitive pixels in the odd rows, three types of color filters are repeatedly arranged in this order. In front of the photosensitive pixels, the first color filter is shifted by 1.5 times the photosensitive pixel edge return period with respect to the odd-numbered row color filter array. The color filter of the first stage 2 and the third color filter are repeatedly arranged in this order nine times; (bl) A solid-state imaging device characterized in that it is configured to be switched when reading out every t-1 rows of the photosensitive pixels to form a signal of a single water eclipse line. 5. The color filter 1 transmits all color light, and the j
The color filter g2 transmits only cyan light, and the third color filter
The solid color filter according to claim 1, wherein the color filter transmits only yellow color light! ! 11 Image device. 6. When imaging under sufficient illuminance, two adjacent rows of the photosensitive pixels are read out simultaneously to form a signal 1&: of one horizontal scanning line, and when imaging is performed under relatively low illuminance, the rows of the photosensitive pixels are read out simultaneously. 5. The solid-state imaging device according to claim 4, wherein the t-1 row is read out in color to form a signal for one horizontal scanning line.