JPH0474908B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a solid-state image sensor for a color television camera, and more particularly to a MOS-type solid-state image sensor that sequentially scans photoelectric conversion elements using an X, Y switch matrix. It is something.

[Prior art]

A solid-state image sensor is a solid-state device that combines a two-dimensional array of pixels with photoelectric conversion and storage functions, and a circuit with a scanning function that sequentially extracts signal charges accumulated in each pixel in time series. It is. Among these, the scanning method is an XY address scanning type (MOS type) using an X, Y switch matrix,
It can be divided into charge transfer types that use CCDs, BBDs, etc. that have self-transfer functions.

FIG. 1 is a configuration diagram of an XY address scanning type (MOS type) solid-state image sensor.

The circuit configuration shown in FIG.
IEEETransED-29No.4PP745-750 (1982, M.
Aoki et al.

In the MOS type solid-state image sensor shown in FIG. 1, the interlace switch 17 is controlled by the output line of the vertical shift register 11, and in odd-numbered fields, the switch 17 is switched to the terminal 18-1, so the horizontal output line O _y1 , O _y are transmitted sequentially at the same time. As a result, in the first horizontal scanning period, 1, 1, 1, 2, 1, 3, 1, 4... and 2,
2 lines of MOS: 1, 2, 2, 2, 3, 2, 4...
Since all transistors are on, the first
The optical signals obtained by the photo diodes 13R, 13G of the rows 1, 1, 1, 2, 1, 3, 1, 4, etc. are transferred to the vertical signal lines 14h, 14g, respectively, and are transferred to the vertical signal lines 14h, 14g, respectively. 2,1,2,2,2,3,2,4
The optical signals obtained by the photo diodes 13G and 13B of ... are respectively transmitted to the vertical signal lines 14f and 14i.
will be moved to

On the other hand, during the horizontal scanning period, the horizontal shift register 12
The output pulses sequentially sent to the output lines O _x1 , O _x2 , O _x3 . The signals on 14i and 14h, 14g are connected to signal output lines 16f, 16i and 16g, 1
Output from 6h. That is, the signal output line 16
The signals of the photo diodes 13R and 13G in the first row are obtained from the signal output lines 1 and 16h.
Signals from photo diodes 13G and 13B in the second row are simultaneously obtained from 6f and 16i.

In the even field, the switch 17 is connected to the terminal 18-2, so that the two signals O _y and O _y2 are sequentially transmitted at the same time. As a result, the two horizontal output lines O _y and O _y2 are simultaneously sent out by the pulse applied from the vertical shift register 11 . As a result, during the first horizontal scanning period, the second row 2,
The optical signals of photo diodes 13G, 13B of 1, 2, 2, 2, 3, 2, 4... are transferred to vertical signal lines 14f, 14i, respectively, and the third row 3,
Optical signals from photo diodes 13R, 13G 1, 3, 2, 3, 3, 3, 4, . . . are transferred to vertical signal lines 14h, 14g, respectively. As a result, during the horizontal scanning period, the second
Optical signals from the photo diodes 13G and 13B in the row are obtained, and optical signals from the photo diodes 13R and 13G in the third row are obtained from the signal output lines 16g and 16h.

In this way, the signal obtained by adding the signals obtained from the signal output lines 16f to 16i has the spatial position weight shifted up or down by one row of photo diodes for each field, so that an interlaced operation is realized. Ru. According to this interlace operation, the optical signals obtained from the photo diodes in all rows are output from the signal output terminal for each field, so when the subject moves, the length of the afterimage that remains on the photo diodes is reduced. The distance corresponds to the distance traveled in one field period (1/60 second), which prevents visually disturbing afterimages.
Furthermore, in combination with the matrix color filter placed in the photodiode, it is possible to simultaneously draw out two completely independent color signals suitable for color signal reproduction, making it extremely advantageous as a single-chip color image sensor. big.

However, in conventional solid-state image sensing devices, when strong light is incident on a part of the screen, false signals such as blooming and smear, which produce bright lines above and below the light spot on the playback screen, occur.

FIG. 2 is a cross-sectional structural diagram of the basic pixel in FIG. 1. The phenomena of blooming and smear will be explained with reference to FIG. 1 is the photo diode
n ⁺ diffusion layer, 2 is P type Si substrate, 3 is n ⁺ diffusion layer, 4
is a vertical signal line, 5 is a gate, 6 and 7 are photoelectrons, 8
is the incident light.

The n ⁺ diffusion layer 1 forming the photo diode is
The photoelectrons 6 generated by the incident light 8 are collected, but if the incident light 8 is too strong, the photoelectrons 6 naturally overflow. These overflowing photoelectrons 6 flow into the n ⁺ diffusion layer 3, that is, the drain, connected to the adjacent vertical signal line 4, and mix with the signals of other pixels that share the vertical signal line 4, that is, the pixels arranged vertically, causing false signals. Generate a signal. This is the blooming phenomenon. On the other hand, smear is Si
The photoelectrons 7 are thermally diffused inside the substrate 2 and flow into the n ⁺ diffusion layer 3, or the n ⁺ diffusion layer 3 is exposed to light by scattered light, so that the vertical signal line is connected regardless of whether the gate 5 is selected. 4, it generates an optical false signal.

The photoelectrons generated at the drain are transferred to the vertical signal line 4 regardless of whether the MOS transistor is on or off.
Since all the drains of the MOS transistors are connected, this type of optical information projected onto each MOS transistor is mixed and added to the vertical signal line 4 and stored. That is, each vertical signal line 4 accumulates a signal current corresponding to the vertical integrated light amount of the projected subject image. This signal appears on the screen superimposed on the normal signal at each horizontal scanning period, so if a subject image with some bright areas is captured, there will be a tail in the vertical direction on the playback screen. A false signal is generated. this is,
This is called vertical smear, which is unique to solid-state image sensors.

In order to suppress these phenomena, a pixel structure as shown in Fig.
(See Publication No. 30350 and the cited documents above).

In FIG. 3, the pixel structure is a three-layer structure consisting of an n ⁺ diffusion layer 1, a thin P-type well 22, and an n-type Si substrate 24, and a parasitic bipolar transistor 25 sucks out excess photoelectrons to the n-type substrate 24 to cause blooming. The smear charge is almost completely suppressed, and the diffusion component of the smear charge is significantly reduced due to the barrier between the P-type well 22 and the N-type substrate 24. Note that the p ⁺ region 23 is an auxiliary means for increasing signal capacity.

However, there is no limit to the amount of incident light, and in practice it is necessary to suppress smear by an order of magnitude or more, and even in the device of the cited document (M. Aoki etal), when put into practical use, it is necessary to further suppress smear by an external auxiliary circuit. Single digit smear suppression is being performed.

Furthermore, conventional solid-state imaging devices have problems in terms of sensitivity, ie, signal-to-noise ratio.

First, for signals, as shown in Figure 1, two vertical signal lines are arranged per column of pixel array.
Since the vertical signal line 14 handles the highest-speed signals, it is essential to use metal such as aluminum (Al). Providing two of these signal lines limits the light entrance aperture of the pixel and reduces the light sensitivity. It's a loss.

Also, regarding the noise, the cited document (M.
As detailed in Aoki et al., there are two main types of parasitic capacitance (first parasitic capacitance) in horizontal scanning.
The internal noise I ² _N1 generated by sampling the vertical signal line 14 having 19) in the figure, the parasitic capacitance of the horizontal signal line 16, the sum of the capacitance Co including the package pin capacitance and the preamplifier input capacitance Ci, and the preamplifier There is preamplifier noise I ² _N2 determined by the equivalent resistance Re of the input section.

Incidentally, each of the above-mentioned noises I ² _N1 and I ² _N2 is expressed by the following equation.

I ² _N1 = 2kTC _v f _s B ……(1) I ² _N2 = 16/3π ² (Co+Ci) ² kTR _e B ³ ……(2) Here, k is Boltzmann constant, T is absolute temperature,
fs is the horizontal scanning frequency, and B is the signal band. These things limit the sensitivity of the solid-state image sensor, but the internal noise I ² _N1 is a component specific to the device.
No matter how good a preamplifier is, it cannot be improved, and the frequency spectrum of the noise is flat, and low frequency components are more noticeable in the reproduced image even with the same noise energy, so this is the dominant factor that limits sensitivity. It is becoming.

FIG. 4 is a circuit diagram of a conventional improved solid-state image sensor.

For example, Journal of the Television Society Vol.26, No.1PP33
46 (Ando et al., 1972), etc., the structure of FIG. 4 is reported. This is perpendicular to the pixel,
two horizontal MOS transistor switches 31,
32, and signals are extracted via the horizontal signal line 36 selected by the vertical scanning line 33 and the vertical scanning line 34. As is clear from Figure 4,
In this element, since sampling of a signal line having a large parasitic capacitance is not performed within the video period, the above-mentioned internal noise I ^2/N1 does not occur. Furthermore, blooming and smearing are limited to cases where a false signal flows into the horizontal signal line 36;
The false signal is cleared every time consecutive pixels are read, and the time is limited to the shortest reading time of one pixel in the horizontal scan.For example, in the case of a standard 500 vertical pixel and 400 horizontal pixel element. , simply, it is reduced to about 1/400 compared to the element shown in FIG.

However, in the device shown in FIG. 4, the MOS transistor 31 connected to the photodiode 13 is
The switching operation continues while the pixel is not selected, but in this case, the MOS
As a common phenomenon in transistors, a charge pump phenomenon occurs in which electrons are extracted from the photo diode 13 and pumped into the substrate. Since this amount varies from pixel to pixel, a fixed noise unique to each pixel is generated, and large fixed variations occur depending on the location on the screen, resulting in poor uniformity and, as a result, sensitivity does not become high.

Furthermore, the horizontal signal line 36 continues to store blooming charges and smear charges for one horizontal line during the non-selection period, that is, for a long period (one field period) minus (one horizontal scanning period), and this amount is This is 250 times larger than the element shown in Figure 1, and this is read out when reading out the first pixel in each horizontal scan, so if the amount of light increases, it will not be possible to read out all in a short time, and the screen will become unstable. .

Additionally, a vertical MOS transistor switch 32
is connected to the horizontal signal line 36, but the coupling capacitance between the gate and drain of the MOS transistor is very large in the on state, and with this connection, all the MOS transistors in one row are in this state when reading signals, and the vertical scanning line A large parasitic capacitance is generated between the signal line 33 and the horizontal signal line 36, resulting in increased preamplifier noise and reduced sensitivity.

Furthermore, the configuration as shown in FIG. 4 cannot read out a plurality of color signals at all times, so it is not suitable for color elements and cannot be adapted to interlaced systems.

[Purpose of the invention]

An object of the present invention is to provide a solid-state imaging device that can improve sensitivity and significantly reduce blooming and smear, in order to improve these conventional problems.

[Summary of the invention]

The solid-state image sensor of the present invention has a pixel array including a photoelectric conversion element and a switch element, and horizontal and vertical scanning circuits for sequentially selectively scanning the pixel array. The element, the switch element driven by the vertical scanning circuit, and the switch element connected to the horizontal signal output line and driven by the horizontal scanning circuit are connected in series in this connection order, and further the horizontal signal output line is connected to the vertical signal line via a switch element driven by the vertical scanning circuit.

[Embodiments of the invention]

FIG. 5 is a circuit configuration diagram of a solid-state imaging device showing an embodiment of the present invention.

The configuration of the present invention shown in FIG. 5 differs from the conventional configurations shown in FIGS. 4 and 1 in the following points, and the advantages thereof are also as follows.

First, two MOS transistors are installed in the pixel ().
Switches 31 and 32 are connected in series, but their connection order is reversed from that shown in FIG. 4, and they are connected in the order from photo transistor 13 to MOS transistors 32 and 31, and an optical signal is sent to horizontal signal line 36. ing. This prevents the charge pump phenomenon from affecting the photodiode 13 during horizontal scanning. () Reset/
Line 47 is provided to eliminate smear signals and charge pump currents, and to read out the signals of all pixels for each field, eliminating afterimages. () A switch 17 is provided to enable the interlaced system. () A plurality of signal output lines 49 and 50 are provided to enable simultaneous scanning of two horizontal lines suitable for single-chip color imaging.

These operations will be explained in more detail.

That is, in the pixel, a photo diode 13 is connected to a vertical MOS transistor switch 32.
This transistor 32 and the horizontal signal line 3
Horizontal MOS transistor switch 31 between 6
Connect. As a result, the charge pump when not selected occurs only on the horizontal signal line 36 and does not affect the signal of the photo diode 13. As is well known, the period of horizontal scanning, that is, the period of the output from the horizontal shift register 12 is very short, and high-speed scanning is performed, whereas the period of vertical scanning, that is, the period of the output from the vertical shift register 11 is very short. The period of the output from the optical sensor is very long, and it is output only once per screen, that is, once when reading an optical signal. Therefore, in FIG. 5, since the charge pump phenomenon in which charge is extracted from the photodiode 13 and pumped into the substrate occurs only during vertical scanning (once per field), the charge pump phenomenon that occurs during each horizontal scanning is Fixed noise is significantly smaller than in the case of FIG. 4, the uniformity on the screen is good, and the sensitivity is high.

Next, regarding scanning, as in the case of the device shown in FIG.
Do rows at the same time. That is, when the interlace switch 17 is switched upward, the output of the vertical shift register 11 turns on all the vertical MOS transistors 32 in the two rows during the first horizontal scanning period, and the horizontal scanning continues in a shorter period. In the scanning period, the horizontal MOS transistors 31 in two rows are turned on one after another by the output from the horizontal shift register 12. As a result, the optical signals of the photo diodes 13R and 13G are transferred to the horizontal signal line 3.
6, and the vertical switch MOS transistor 37 is turned on by the output of the vertical shift register 11, so that the optical signals sent to the horizontal signal lines 36 for two rows are transferred to separate vertical signal lines 4.
Moved to 1,42. Thereby, optical signals in two horizontal rows can be simultaneously output to independent signal output lines 49 and 50.

Since an interlaced system can be realized, the signals of all pixels can be read out for each field, and no visually disturbing equivalent afterimages occur. In addition, in color development, multiple color signals must be output simultaneously, but as shown in Figure 5, multiple vertical signal lines are provided, making it possible to perform color development. Become something. Note that when used as a monochrome element, the vertical signal lines 41 and 42 may be combined into one.

Next, in the reset MOS transistor 48,
Reset for each blanking period of each horizontal scan.
A positive pulse is applied via line 47 to reset all horizontal signal lines 36 to the voltage of video power supply 40. By this means, the blooming charges, smear charges, and charge pump charges received by the horizontal signal line 36 are discharged every horizontal scanning period and no longer become a problem. That is, there is a large parasitic capacitance in the horizontal signal line 36, and blooming charges and smear charges are accumulated here for a long period of one horizontal scanning period, but since they are all discharged by the reset MOS transistor 48, the smear does not occur. This decreases to 1/400 of the case in Figure 4.
Moreover, this reset MOS transistor 48 is
Since it is connected to the horizontal signal line 36, the sampling noise generated during the discharge process is removed from the vertical switch.
By activating the MOS transistor 37, it is wiped out before the signal is read out, so that it will not be mixed into the signal. This means that, in the conventional example shown in FIG. 1, for example, the amount of random noise (sampling noise) generated can be significantly reduced compared to the case where the vertical signal line 14 is discharged in the same way as above, and the amount of random noise (sampling noise) can be significantly reduced. It is also extremely effective. Note that the horizontal scanning line 36 uses metal such as aluminum (AL), and the vertical scanning line 33 uses gate wiring material such as polycrystalline silicon (Si), but most parts can be formed by overlapping. . As a result of this,
Since the aperture of the photo diode 13 can be increased and, as mentioned above, internal noise is eliminated, the sensitivity is greatly improved.

Note that it is possible to change the photodiode to a phototransistor for the pixel structure shown in FIG. 5, or apply the improved pixel structure shown in FIG. 3, thereby achieving even higher performance. element can be realized. Furthermore, regarding the reset method, output method, etc. in each horizontal blanking period of the horizontal scanning line 36, the simplest method has been explained in the embodiment, but even though the basic concepts of the reset operation and the independent output operation of multiple signals are the same, Ba,
Other methods are also applicable without being limited to this. Furthermore, although the embodiments have been described using an n-channel element, the present invention can be applied to a p-channel element in exactly the same way by connecting the polarities in reverse.

〔Effect of the invention〕

As explained above, according to the present invention, a switch element driven by a vertical scanning circuit and a switch element driven by a horizontal scanning circuit are connected in series between a photoelectric conversion element and a horizontal signal line. Since the elements are inserted in this connection order, it is possible to realize a high-sensitivity solid-state image sensor without generating optical false signals such as blooming or smear.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional MOS type solid-state image sensor.
Figure 2 is a cross-sectional structural diagram of the basic pixel in Figure 1;
FIG. 3 is a cross-sectional structural diagram of a conventional improved basic pixel, and FIG. 4 is a circuit diagram of a conventional improved solid-state image sensor.
FIG. 5 is a circuit diagram of a solid-state imaging device showing an embodiment of the present invention. 1, 3...n ⁺ diffusion layer, 2...P-type Si substrate, 4...
... Vertical signal line, 5 ... Gate, 11 ... Vertical scanning circuit (shift register), 12 ... Horizontal scanning circuit (shift register), 13 ... Photo diode, 17 ... Interlace switch, 3
3...Vertical scanning line, 36...Horizontal signal line, 34,
41, 42...Vertical signal line, 31...Horizontal MOS
Transistor switch, 32... Vertical MOS transistor switch, 37... Vertical switch
MOS transistor, 48...reset transistor, 38, 45, 46...preamplifier.

Claims (1)

[Scope of Claims] 1. A solid-state image sensor having a pixel array including a photoelectric conversion element and a switch element, and a horizontal and vertical scanning circuit for sequentially selectively scanning the pixel array, in which the photoelectric conversion element is and a switch element driven by a vertical scanning circuit,
Switch elements connected to the horizontal signal output line and driven by the horizontal scanning circuit are connected in series in this connection order, and furthermore, the horizontal signal output line connects another switch element driven by the vertical scanning circuit. A solid-state image sensor, characterized in that it is connected to a vertical signal output line through a vertical signal output line. 2. Claim 1, further comprising a mechanism for resetting the horizontal signal output line to a predetermined voltage every blanking period of horizontal scanning.
The solid-state image sensor described in . 3 The horizontal signal output lines are selectively scanned simultaneously in two horizontal rows whose combinations change for each field;
3. The solid-state image sensor according to claim 1, wherein an optical signal is transmitted. 4. The solid-state imaging device according to claim 1, 2, or 3, wherein the horizontal signal output lines are connected to independent vertical signal output lines.