JPS587983A - Solid-stage image pickup element - Google Patents

Abstract

PURPOSE:To obtain an image pickup signal having a high SN ratio, by constituting A MOS for horizontal switch with N channel enhancement type MOS transistors and P channel enhancement type MOs transistors. CONSTITUTION:A metal oxide semiconductor MOS transistor TR for horizontal switch which reads out the signal current of each of picture elements arranged in the row direction consists of N channel enhancement type MOS TRs 12 (12am 12b, and 12c) and P channel enhancement type MOS TRs 13 (13a, 13b, and 13c) connected in parallel to TRs 12. In this case, since NMOS TRs 12 and PMOS TRs 13 are changed from the turn-on state to the turn-off state simultaneously, electrons and positive holes are distributed simultaneously to drain and source electrodes from TRs 12 and TRs 13 respectively, and currents of spike noises are in directions opposite to each other hand and are cancelled. When TRs 12 and 13 are changed from the turn-off state to the turn-on state, the similar operation is performed. Thus, the absolute value and the variance of spike noise currents are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state image sensor, and particularly to an MO8 solid-state image sensor that can reduce spike noise generated during signal readout and obtain an image signal with a high S/N ratio.

Generally, solid-state image sensors include CCD (ChargCouple).
The MOS
) MOS (Metal 0x-de S
em1conductor) system, and the present invention is inspired by the latter MO8 system.

FIG. 1 is a circuit diagram showing an example of a conventional MO8 type solid-state image sensor. In the figure, pixels 3 composed of a photodiode 1 and a vertical switch Mos transistor (hereinafter referred to as VMO 8) 2 are arranged in row and column directions, and these pixels 3 are connected to a horizontal scanning circuit 4 and a vertical scanning circuit 5. Video bias 6 to the pixel selected by
load resistance γ, horizontal switch MO8) transistor (
A charging current flows through the VMO 8 (hereinafter referred to as 5MO8) and the VMO 82, and the voltage drop due to the load resistance γ is detected as an optical signal, which is amplified and subtracted by the video amplifier 10 via the capacitor 9. 1. In this case, when reading signal charges, the pulse voltage SIt sl shown in the pulse timing diagram in FIG. Pulse ii pressure s, lS4
．． S, are applied sequentially. Then, a signal output S6 is output to the horizontal signal line 11.

In this case, the signal output S6 is a signal obtained by combining the signal charge accumulated in the photodiode 1 and the spike noise S7 generated when the 5MO 88 is opened and closed.

However, in the MO8 type solid-state image sensor with the above configuration, since 5MO88 has a large capacitance component under its gate electrode, the spike noise generated when 5M088 opens and closes is larger than the signal charge, as shown in Figure 2 S. In addition, if the capacitance component under the gate electrode of 5MO88 is parallel due to minute deviations (variations) caused by microfabrication of the semiconductor, the size of the spike noise S7 itself will be It will be different. For example, as shown in Fig. 2, the spike noise S7 generated in 5MO88c is
If it is larger than MO88a, ab, pixels 3c, 3
c', that is, large variations occur when reading out the photodiodes 1 in a single column, and since they occur randomly due to processing, they cannot be removed even by using a noise removal circuit such as a low-pass filter. There wasn't. For this reason, in the case of two-dimensional solid-state imaging devices, vertical striped noise called fixed pattern noise occurs due to variations in this spike noise, causing a significant decrease in the S/N ratio of the imaging signal. .

Therefore, in the present invention, by configuring the 5MO8 section with an N-channel enhancement type MO8) transistor (hereinafter referred to as NMO8) and a P-channel enhancement type MO8) transistor (hereinafter referred to as PMO8), the deviation of the capacitance component ( A solid-state imaging device that suppresses the occurrence of spike noise by reducing the variation (γ variation), and reduces the fixed pattern noise that occurs due to the variation of this spike noise in the secondary element, and obtains an imaging signal with a high 87N ratio. is intended to provide.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 does not show an example of the solid-state image sensing device according to the present invention, but shows the main part of the cross-sectional groove, and since the same symbols as in the previous drawings represent the same elements, the explanation thereof will be omitted. In the same figure, MO8 for the horizontal switch reads out the signal current of each pixel arranged in the column direction.
)7 transistor section is connected in parallel to NMO812, which has the same function as the conventional 5MO88.
It is composed of O813. And NMO81
2 is applied with the e output pulse equivalent to the conventional one from the horizontal scanning circuit 4, while the PMO 813 is formed with a circuit configuration in which an inverted output pulse of the above-mentioned output pulse is applied. ing. 1 In such a configuration, from the horizontal scanning circuit 4 to the NMO8
The video bias Vv is set to an intermediate level between the high level VH and the low level VL of the output pulses applied to the NMO 312 and PMO 813.
The threshold voltage vth of 813 is VH-vv>vth (NMO812) 9 Φ・ψ
(1) VV-VL> : vth + (PMO81
3) When the condition φ(2) is satisfied, the NMO 812 and the PMO 813 are turned on at the same time, and a signal is read out to the horizontal signal line 11. In this case, the spike noise component that occurs when the NMO 812 turns from on to off is generated because the electrons induced under the gate when the NMO 812 is on are distributed to the drain and source electrodes when the NMO 812 is off.

On the other hand, the spike noise component that occurs when the PMO 813 turns from on to off is generated because holes that were induced under the gate when the PMO 813 is on are distributed to the drain and source electrodes when the PMO 813 is off. Therefore, in the above configuration, NMO812 and PM
Since O813 turns from on to off at the same time, electrons from NMO812 go to the drain and source electrodes, and electrons from PMO
Holes are distributed from 813 at the same time. In other words, the current directions of spike noise are opposite to each other,
They will cancel each other out. Further, when the NMO 812 and the PMO 813 are turned on from off, spike noise currents similarly flow in directions that cancel each other out. In this way, the spike noise current itself can be reliably reduced. Therefore, fixed pattern noise caused by variations in spike noise current can also be reduced. Furthermore, even if a processing deviation (variation) due to the semiconductor processing process occurs in NMO812 and PMO813, since NMO812 and PMO813 are connected in parallel, it is considered that NMO812 and PMO813 have almost the same deviation (variation). , PMO81
Cancellation of spike noise by No. 3 acts in the direction of reducing the deviation. That is, not only the absolute value of spike noise but also its variation can be reduced.

Note that the NMO 812 of the 5MO8 section is the horizontal scanning circuit 4. Similarly to the vertical scanning circuit 5 and photodiode 1, N
The PMO 813 can be easily manufactured by a normal CMOS process, such as forming on a P region formed by ion implantation or the like on a substrate, and forming the PMO 813 on an N substrate without a P region.

Furthermore, in the above embodiment, an MO8 type solid-state image sensor in which pixels are arranged two-dimensionally in M columns and N rows is described, but the present invention is not limited to this, and pixels are arranged in one-dimensionally in M columns. Of course, the same effects as described above can be obtained even if the present invention is applied to an MO8 type solid-state image sensor.

As explained above, according to the present invention, it is possible to reduce spike noise and also to reduce fixed pattern noise caused by variations in this spike noise, thereby significantly improving the quality, reliability, etc. of the MO8 type solid-state image sensor. In addition, the preamplifier circuit that amplifies the signal from the image sensor has low spike noise, so it can have a high amplification factor, making it possible to increase the S/N and simplify the peripheral circuitry, improving the performance of the camera itself. 1. You can get extremely excellent effects such as being able to measure

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional MO8 type solid-state image sensor, FIG. 2 is a pulse timing diagram thereof, and FIG. 3 is a circuit diagram showing an example of a solid-state image sensor according to the present invention. be. 12a, 12b, 12c11 fist...N-channel enhancement type MOS transistor (NMO8), 13a
I 13b, 13c@-P channel enhancement type Mos+ transistor.

Claims (1)

[Claims] Photodiode and vertical switch MOS that accumulate optical signals
A solid-state image sensor configured such that pixels formed by transistors are arranged at least in a column direction, the pixels are selected by a horizontal scanning circuit and a vertical scanning circuit, and a signal current is read out by a horizontal switch MO8) transistor, The horizontal switch MO8) transistor,
A solid-state image sensing device characterized in that MO8+- transistors whose movable charges are charges of opposite polarity are connected in parallel.