JPH0473674B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a solid-state imaging device for a color video camera.

Configuration of conventional example and its problems In recent years, color video cameras using solid-state imaging devices are rapidly becoming popular. There are various types of solid-state imaging devices, but here we will discuss in detail the occurrence of white spot defects or black spot defects, using an imaging device called a MOS type imaging device that uses a photodiode and a MOS field effect transistor as an example.

FIG. 1 is an example showing the operating principle of a MOS type image sensor. That is, a large number of photodiodes 1, which are photosensitive elements, are arranged in a matrix, and a horizontal shift register 2, a vertical shift register 3, and horizontal changeover switches 41, 42, 43, . Changeover switches 51, 52, . . . 5m are provided. As is well known, the horizontal shift register 2 is driven by a start pulse and a horizontal clock pulse synchronized with a horizontal synchronizing signal, and switches 41 and 4 are driven by a start pulse and a horizontal clock pulse.
Switches 2, 43, . . . , 4n are sequentially opened and closed to operate all the switches within one horizontal scanning time. On the other hand, the vertical shift register 3 is driven by a start pulse synchronized with the vertical synchronizing signal and a clock pulse synchronized with the horizontal synchronizing signal, and switches 51, 52, .

By operating these two types of switches, the charge stored in the photodiode is sequentially supplied to a load circuit composed of a resistor 6 and a power supply 7, and is taken out as a voltage signal.

Here, if the photodiode 1A is destroyed for some reason and the substrate and cathode are short-circuited, the signal from the photodiode 1A always reaches the signal saturation point and becomes extremely large.

Further, a large signal voltage is also generated when leakage occurs in the photodiode and the dark current of the photodiode is abnormally large.

These are collectively referred to as white spot defects of the image sensor, and the level of the latter varies depending on the operating temperature, operating voltage, etc. of the image sensor.

Further, if the situation is opposite to the above, a black spot defect occurs, but the black spot defect is not very noticeable on the screen.

FIG. 2a shows the state of a black dot defect in the horizontal line signal, and FIG. 2b shows the state of a white dot defect in the horizontal line signal. The shaded area in FIG. 2 indicates the amount of signal generated in the photodiode 1 depending on the amount of received light, and a indicates the case where there is no signal at the defective position, and b indicates the case where the signal at the defective position is saturated.

FIG. 3 shows an example in which such black spot defects and white spot defects are replaced and corrected with the signal amount of the picture element one picture element before.

The operation of the conventional example shown in FIG. 3 will be explained below with reference to FIG. 4. The solid-state image sensor 8 is driven by a pulse generation circuit 9, and pulses in a synchronous relationship with the solid-state image sensor 8 are supplied to a first sample-and-hold circuit 10 and a second sample-and-hold circuit 11. FIG. 4a shows the signal state of a horizontal line with a defect, and position D is a black dot defect. 4b shows the first sample and hold pulse, c shows the output of the first sample and hold circuit 10, d shows the second sample and hold pulse, and e shows the output of the second sample and hold circuit 11.

The first sample and hold pulse is passed through the defect position memory circuit 12 to the first sample and hold circuit 1.
0, and the defect location storage circuit 12 functions to stop the first sample and hold pulse (see FIG. 4b) at the defect location. Therefore, since the output of the first sample and hold circuit 10 does not sample and hold the defective position as shown in FIG. be done. When this signal is passed through the second sample-and-hold circuit 11 with the second sample-and-hold pulse shown in d, the portion at the defective position D is corrected with the previous pixel signal C, as shown in FIG. 4e. The conventional example shown in FIG. 3 is effective for black-and-white video camera devices, and defective parts other than edge parts can hardly be identified.

However, single-chip color solid-state imaging devices
As shown in the figure, mosaic color filters 14, 15, and 16 are often arranged above the photodiode 1. For example, the red filter 14,
When the green filter is 15 and the blue filter is 16, one photodiode corresponds to one photodiode, and one filter corresponds to each filter.

Now, if the signal voltages obtained from the corresponding photodiodes of the red filter 14, green filter 15, and blue filter 16 are R, G, and B, then for each horizontal line, there are n columns of R, G, R, G, and B, G, B, G
Dot sequential signals are obtained alternately, such as in the n+1 columns of .

If the photodiode 1A in column n in FIG. 5 is defective, the signal G of the green filter 15 is missing, and this position becomes a white dot defect or a black dot defect. When defect correction is performed using the signal, the signal voltage of the previous pixel signal R is replaced in the signal part of G, but the green filter 1
5 and the red filter 14 each have different amounts of light transmission, so the G signal voltage and the R signal voltage are different, and the brightness of the defective part is also different, resulting in the problem that sufficient correction cannot be obtained.

Purpose of the Invention The present invention solves the above-mentioned problems of the conventional technology.
It is an object of the present invention to provide a solid-state imaging device that corrects a defect position so as to make it less noticeable by adding the previous picture element signal and the picture element signal two pixels before the defect position.

Structure of the Invention The present invention includes a pulse generation circuit, a solid-state image sensor driven by the pulse generation circuit, a defect position storage circuit driven by the pulse generation circuit, and a sample hold pulse for removing defective positions by the defect position storage circuit. is supplied, and a first sample and hold circuit connected to the output section of the solid-state image sensor and a defect position storage circuit supply sample and hold pulses except for one pixel before the defective position and the defective position,
The solid-state imaging device includes a second sample-and-hold circuit connected to the output section of the solid-state imaging device, and an adder that adds the output signals of the first and second sample-and-hold circuits, Since the output signal of the defective position is corrected with a signal obtained by averaging the previous picture element signal and the two previous picture element signals, the defective position can be made hardly noticeable.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention having the above configuration is shown in FIG. 6, and main waveforms of its symbols are shown in FIG. 7. In FIG. 6, the same numbers as in FIG. 3 are the same or have equivalent functions.

In FIG. 6, 17 is a first sample and hold circuit, 18 is a second sample and hold circuit, 19 is an adder, and 20 is a sample and hold circuit.

The operation of the solid-state imaging device of this embodiment configured as described above will be described below.

The solid-state image sensor 8 is driven by the pulse generating circuit 9, and an output signal a is obtained. FIG. 7a shows the output signal of the horizontal line, which is an example in which there is a defect at position D. This defect position D indicates a black spot defect, but the output signal a of this solid-state image sensor 8 is
7 and 18, and are supplied with sample and hold pulses b and d, respectively. The first sample-and-hold circuit 17 is supplied with the sample-and-hold pulse b excluding the portion at the defective position D.
The sample is held as shown in .

The second sample and hold circuit 18 has a defective position D.
Since the sample and hold pulse d excluding the position one pixel before the defective position D is supplied, the pixel signal B two pixels before the defective position D is sampled and held up to the defective position D as shown in e. .

As already explained using FIG. 5, in a single-plate color solid-state imaging device, mosaic-like color filters 14, 15, and 16 are often arranged on the photodiode 1. As shown in the figure, if one color filter (red filter, green filter, or blue filter) corresponds to one photodiode, the output signal will be R, G,
Since dot sequential signals are obtained alternately such as n columns of R, G... and n+1 columns of B, G, B, G..., the horizontal line signal output in Fig. 7a shows the B pixel output and the defect position. The color filters of D, A picture element output, C picture element output, and E picture element output are the same.

First and second sample and hold circuits 17, 18
The output signals c and e are connected to an adder 19 and added to obtain an output signal f. In the output signal f of the adder 19, the signal part of the defective position D and the pixel signal part of one pixel before the defective position D are the same as the pixel signal of the one pixel before the defective position D and the pixel signal part two before the defective position D. The summed signal with the pixel signal of is obtained, and the other obtained signal is
In each case, twice the output signal h is obtained.

Since the output signal f of the adder 19 is added while the sample and hold pulses at the defect position D and the previous pixel position are stopped, a wave measurement band other than the frequency of the sample and hold pulse is generated, which is preferable. do not have.

Normally, a sample and hold circuit 20 is added as shown in FIG. 6, and the output signal f of the adder 19 is sampled and held using the sample and hold pulse g.
An output signal h is obtained. When this output signal h is restored to the original magnitude of the output signal of the solid-state image sensor, the output signal at the defective position D and the output signal at the pixel position immediately before the defective position D are the same as those for the pixel B. The signal and the C pixel signal are corrected using the averaged signal. This corrected output signal h is converted into a DC component by the signal processing circuit 13 through, for example, a color carrier frequency trap circuit, so that the defect position becomes less noticeable. In this case, care must be taken as color false signals will occur unless the color signals at the defect position and the position one pixel before the defect position are turned off.
Since the color signal passes through a low-pass filter,
The color signal portions at the defective position and the position one pixel before the defective position are interpolated, making the defective position less noticeable and the circuit configuration simple.

Effects of the Invention The solid-state imaging device of the present invention has a first sample-and-hold circuit to which a sample-and-hold pulse is supplied except for the defective position by the defective position memory circuit, and a sample-and-hold circuit for all but the defective position and one pixel before the defective position. By providing a second sample-and-hold circuit to which pulses are supplied and an adder that adds the outputs of each of the first and second sample-and-hold circuits, the circuit configuration is simple, and the picture immediately before the defective position can be Since the output signal of the defective position is corrected with a signal obtained by averaging the pixel signal of the pixel and the signal of the two previous pixel, the defective position can be made hardly noticeable, which has a great practical effect.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an example of a MOS type solid-state imaging device, Figures 2a and b are horizontal line output voltage waveform diagrams showing black spot defects and white spot defects, and Figure 3 is a conventional monochrome solid-state imaging device. Fig. 4 is a waveform diagram of essential parts of defect correction in a conventional monochrome solid-state imaging device; Fig. 5 is a diagram showing an example of a color separation method for a single-chip color camera; Fig. 6 7 is a schematic configuration diagram of a solid-state imaging device according to an embodiment of the present invention, and FIGS. 7a to 7h are waveform diagrams of essential parts of an embodiment of the present invention. 8... Solid-state image sensor, 9... Pulse generation circuit,
12... Defect position storage circuit, 13... Signal processing circuit, 17... First sample hold circuit, 18...
...Second sample and hold circuit, 19...Adder,
20...Sample hold circuit.

Claims (1)

[Claims] 1. A pulse generation circuit, a solid-state image sensor driven by the pulse generation circuit, a defect position storage circuit driven by the pulse generation circuit, and a sample hold pulse is supplied by the defect position storage circuit except for the defect position. , a first sample and hold circuit connected to the output section of the solid-state image sensor and the defect position storage circuit supply a sample and hold pulse to the defect position and the area one pixel before the defect position, and A solid-state imaging device comprising: a second sample-and-hold circuit connected to an output section; and an adder that adds output signals of the first and second sample-and-hold circuits.