KR820002286B1 - Solid-state image apparatus - Google Patents

Abstract

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Description

Solid-state imaging device

1 is a diagram showing a schematic configuration of a conventional solid state image pickup device.

2 shows an equivalent circuit of the signal reading circuit.

3 is a waveform diagram for explaining fixed pattern noise.

4 is a diagram showing the configuration of one embodiment of the present invention.

FIG. 5 is a waveform diagram for explaining the operation of the embodiment of FIG.

6 is a diagram showing the configuration of another embodiment of the present invention.

7 is a waveform diagram for explaining the operation of the embodiment of FIG.

8 is a diagram showing the configuration of another embodiment of the present invention.

FIG. 9 is a waveform diagram for explaining the operation of the embodiment of FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid state imaging device, in particular, a solid state imaging device which reduces fixed noise pattern noise inherent in the solid state imaging device.

The solid state imaging device is attracting attention as a small size television camera, which is superior to an imaging tube in terms of good safety, long life, low power consumption, and simple handling.

The solid-state image pickup device is usually arranged in a two-dimensional image to constitute an imaging pixel matrix, a switch device for selecting (x, y) coordinates corresponding thereto, and a switch device for opening and closing the switch device. x (horizontal) and y (vertical). FIG. 1 shows a schematic configuration for explaining the operation of the solid state image pickup device.

In the figure, 1 is a horizontal scan for x position selection, 2 is a vertical scan for y position selection, and 3 is a vertical switch MOS transistor for opening and closing according to the scanning level from the circuit 2 (hereinafter, referred to as vertical switch). do). 4 is a photodiode (photoelectric conversion element) using a source junction of the vertical switch 3, 5 is a vertical signal output line commonly connected to the drain of the vertical switch 3, and 6 is a horizontal scan (1) A horizontal switch MOS transistor (hereinafter referred to as a horizontal switch) for opening and closing in accordance with a scanning pulse from the drain is connected to a horizontal signal output line 7 and a source to a vertical signal output line 5.

8 is a reference power source connected to the horizontal signal output line 7 via a resistor 9.

The common feature of the solid-state image pickup panel is that pixels are separated separately, and scanning is performed by clock pulses applied from the outside to the horizontal and vertical scans to easily determine which pixel signals are currently being read. You can do it.

Next, a signal reading method from the solid state image pickup device shown in FIG. 1 will be described as FIG. 2 is a diagram showing an equivalent circuit of one pixel (photodiode), horizontal and vertical switches, and a reference power supply.

When light is not incident, the constant charge Qo determined by the constant voltage 8 applied to the element is stored in the parasitic capacitance Co of the photodiode 4. When light is irradiated, charges proportional to the amount of irradiated light are discharged through the photodiode 4.

The vertical switch 3 is turned on by a signal to the vertical scan introduced via the terminal 3-1, and the horizontal switch 6 is turned on by a signal to the horizontal scan introduced via the terminal 6-1. When it is turned ON, a current flows to replenish the electric charges discharged from the reference power supply 8, and the charge of the parasitic capacitance Co of the photodiode 4 is charged until it becomes Qo again. The signal reading is performed by detecting the incoming current by the load resistor 9. C ₁ and C ₂ are parasitic capacitances generated according to the structure of the device, and signals are read out at these capacitances and time constants determined by the ON resistance and the load resistance 9 of the horizontal switch 6.

3 shows an output signal B and a signal output A to the horizontal scan. The signal output A is superimposed on the differential signal DS (spike noise) as shown in the figure by the capacitance Cp between the gate and the source and the gate and the drain of the horizontal switch 6 in addition to the optical signal indicated by the diagonal lines. It becomes a signal. Since the waveform of the superimposed spike noise differs depending on the location of the image pickup device, there is a problem of deteriorating image quality due to fixed vertical streak noise (hereinafter referred to as fixed pattern noise). In addition, To shown in FIG. 3B represents the ON time of the horizontal switch 6.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and its object is to provide a solid state image pickup device with less deterioration in image quality by removing the fixed pattern noise.

In order to achieve the above object, in the present invention, the spike noise, which is a large factor of the fixed pattern noise, is almost the same or reversed in the rise and fall of the opening and closing pulses of one horizontal switching element. The fixed pattern noise is removed by using the.

4 shows a block diagram of one embodiment of the signal processing circuit of the present invention, and FIG. 5 shows its signal waveform. And the optical signal component is shown by the dotted line. In FIG. 4, 11 is the solid state image pickup device shown in FIG. The output signal (figure 5a) of the image pickup device 11 is input to two sample hold circuits 13 and 14 (hereinafter referred to as S / H circuit) via the preamplifier 12, and FIG. Then, the sample is held by the sample pulse shown in FIG. 5C, and the signals are shown in FIGS. 5D and 5E, respectively. The signal of FIG. 5d is delayed by the delay circuit 15 by the ON time TO of the horizontal switch 6 to (F), and is added to the 5e degree by the addition circuit 16 to the final output 5g degree.

Since the spike noise is a waveform substantially symmetrical with respect to the average level, the signal 5g is a signal with little spike noise, and the fixed pattern noise is greatly reduced.

The sample pulses of the S / H circuits 13 and 14 are monostable multivibrators 18, 19, and (19) with reference to the horizontal clock pulses 21 driving the horizontal scanning path of the image pickup device 11. 20) can be easily formed.

Another embodiment of the present invention is shown in FIG. 6 and FIG. 6 is a block diagram of one embodiment of the signal processing circuit of the present invention, and FIG. 7 is a waveform diagram for explaining the operation thereof.

In this embodiment, the P point of the output signal of the image pickup device shown in Fig. 7A and the q point at which the magnitude of the spike noise are almost uniform with P are sampled, and the signal held at the q point is delayed to the P point. By taking the signal, a signal without spike noise is obtained. The output 7a of the image pickup device 11 is input to the S / H circuits 13 and 14 and sampled with the pulses of FIGS. 7b and 7c.

The output of the S / H circuit 13 sampled in the pulse 7c is inputted to the S / H circuit 22 and sampled again in the pulse 7b to signal the time difference between the pulse 7c and the pulse 7b. Is delayed, the outputs of the S / H circuits 22 and 44 are input to the subtractor 17, and the output of the S / H circuits 14 is subtracted from the output of the S / H circuits 22. It becomes a signal without the same spike noise, and can reduce a fixed pattern drastically. The sample pulses 8b and 8c may be easily formed by the monostable multivibration 18 and the pulse delay line 23 based on the horizontal clock pulse 21.

8 shows a third embodiment in which the present invention is applied to a color solid state image pickup device.

In the figure, 30 denotes a single-plate color solid-state image pickup device, and a signal in which the antler signal, the application signal, and the blue signal are alternately output to the two output terminals. It is a structure obtained.

Such a structure is described, for example, in U.S. Serial No. 92398. However, the two-phase clock pulses to the horizontal scanning of the imaging device 30 are 3.58 MHz and the horizontal scanning pulses are 7.16 MHz, respectively.

The application signal, the blue and red antler signals passed through the amplifiers 31 and 32 are input to the low pass filters (LPFs) 33 and 34, respectively. The LPFs 33 and 34 pass a signal component of 7 MHz or less. This cuts the harmonic content of 7.16 MHz and improves S / N. 35, 36, 37, 38, 39, and 40 are S / H circuits, respectively, and sample the desired signals at respective timings.

41, 42, and 43 are adder circuits, respectively, and output an application signal, a blue signal, and a antler signal without fixed pattern noise. 47 is a control pulse generating circuit. 9 shows waveforms of respective parts of the embodiment of FIG.

9A and 9B show two-phase clock pulses of the imaging device 30 to the horizontal scan, and FIG. 9C shows a horizontal scanning pulse, that is, an opening / closing pulse of the horizontal switch, and FIG. 9D shows an output waveform of the imaging device 30. and the hatched portion sample of the optical signal part, a 9e turn LPF (33), and 34 is an output waveform, the scan line for the optical signal part, a 9f also f ₁ is S / H circuit 36, 40 pulse, f ₂ is sampling pulses of the S / H circuits 38 and 40, and g ₁ is the sampling pulses of the S / H circuits 35 and 39, and g ₂ is the S / H circuit 37, Sampling pulse of (39). As can be seen by comparing FIG. 9D and FIG. 9E, the phase relationship between the sampling pulses is different from that of FIG. 5 because the optical signal portion is delayed by the LPF.

In the above embodiment, the timing of the first sampling is the position where the signal is the maximum, and the second sampling is performed at the position where spike noise of the same in phase or inverse phase appears in the same position as this position. However, even if the positions of the second sampling are somewhat different, the adjustment may be made so that the fixed pattern noise is minimized at the rate of addition and subtraction.

As described above, the use of the present invention makes it possible to reduce the fixed pattern noise to less than half of the conventional one, and to realize the practical use of the solid state image pickup device.

Claims (1)

A group of photoelectric conversion elements 4 arranged in two dimensions, a group of vertical switch elements 3 whose input ends are connected to each of the photoelectric conversion elements 4, and the vertical switch element 3 The control terminal of the horizontal switch element 6 and the vertical scan circuit 2 for applying vertical scan pulses to the control terminal of the vertical switch element 3 and the horizontal switch element 6 connected to the output end thereof. In a solid state imaging device (1) configured to apply a horizontal scanning pulse to a laser beam, the solid state imaging device (1) comprising: first and second sampling and holding of spike noise generated by the horizontal switch element (6) at different predetermined points in time; And means for performing a predetermined calculation on the output from said first and second means.

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