JPH04213976A - Imaging device - Google Patents

Abstract

PURPOSE:To provide the image pickup device which can suppress noise with simple circuitry. CONSTITUTION:This image pickup device has the solid-state image pickup element which has a non-signal period and signal period in the period corresponding to a picture element and outputs the signal having the same noise in both periods, a biasing means 103 which applies uniform bias light to the image pickup region of the solid-state image pickup element 101 or applies a bias charge to the signal period of the output signal to increase a signal level, a noise extracting means 105 which extracts the noise of the non-signal period by clipping the specified level or above of the signal of the signal period, and an arithmetic means 107 which removes the noise obtd. by the noise extracting means 105 from the output signal of the solid-state image pickup element 101.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device using a solid-state imaging device, and more particularly to an imaging device capable of removing noise from an output signal of a solid-state imaging device.

[Summary of the Invention] The present invention is a solid-state imaging device that has a no-signal period and a signal period for each pixel of the output signal, in which noise can be removed from the output signal of the device. In the present invention, first, the output signal level is increased by applying constant bias light to the imaging region or applying bias charges during the signal period of the output signal. Next, noise is extracted from the no-signal period by clipping the signal during the signal period of the output signal from the solid-state image sensor at a constant level. The noise in the image signal is removed by subtracting the extracted noise from the image signal from the element.

0003

2. Description of the Related Art It is known that reset noise occurs in an image pickup apparatus using a fixed image pickup element made of, for example, a charge transfer device (CCD).

FIG. 5 is an explanatory diagram of reset noise generated in the solid-state image sensing device. Here, the noise generation mechanism will be explained below assuming that the solid-state image sensor is a CCD, and the output stage of the horizontal transfer CCD register is configured with a floating diffusion amplifier.

As shown in FIG. 5, the signal waveform output from the horizontal transfer CCD register includes a reset period 501 and a no-signal period (field-through period) for one pixel.
503 and a signal period 505. Here, the output level in the field-through period 503 does not remain at a constant level but takes various values (N1, N2, . . . ) due to variations in the amount of charge reset in the reset period 501. In the signal period 505, the signals (S1, S2,...
) during the field-through period (N1,
N2,...) are superimposed, and this becomes noise. This is called reset noise. Also, horizontal transfer C
Noise is also generated in the output amplifier downstream of the CD register. This noise is superimposed over all of the reset period 501, field-through period 503, and signal period 505, but if the frequency of this noise is less than the frequency of one pixel, the field-through period 503 also overlaps with the signal period 505.
are the same, so it can be treated in the same way as the reset noise described above.

[0006] Conventional methods for suppressing the noise generated in the image sensor include the correlated double sampling method ("Charge Transfer Device" published by Kindai Kagakusha) and the CCS method (
“A Tree-CCD HDTV Color Ca
"mera" SMPTE Journal, July
1990) etc.

However, since the correlated double sampling method requires sampling for each pixel, a high-speed sampling circuit is required, resulting in a complex circuit and high power consumption. Additionally, noise above the Nyquist frequency was aliased and entered the band.

[0008] Furthermore, in the CSS method, sampling is not performed for each pixel, but clamping is performed for each pixel, so
Similar to correlated double sampling, a high-speed clamp pulse is required, and generating the high-speed pulse consumes a lot of power.

[0009]

[Problems to be Solved by the Invention] As described above, in the case of the above-mentioned conventional noise suppression method, since the correlated double sampling method requires sampling for each pixel, a high-speed sampling circuit is required, and the circuit is complicated. The disadvantage is that it consumes more power. Another drawback is that noise above the Nyquist frequency is folded back and enters the band.

[0010] Furthermore, in the CSS method, sampling is not performed for each pixel, but clamping is performed for each pixel, so
Similar to correlated double sampling, this method requires high-speed clamp pulses, and has the disadvantage that it consumes a lot of power to generate the pulses. In addition, there is a problem in that these high-speed pulses are superimposed on the output image signal within the imaging device through some path, such as ground or power supply, resulting in noise.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an imaging device that can eliminate the drawbacks of the prior art described above and suppress noise with a simple circuit configuration.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention has a no-signal period and a signal period in a period corresponding to a pixel, and has the same noise in both periods, as shown in FIG. Applying uniform bias light to a solid-state image sensor 101 that outputs a certain signal and an imaging area of the solid-state image sensor 101,
Alternatively, the bias adding means 103 increases the signal level by applying a bias charge to the signal period of the output signal, and the signal from the solid-state image sensor 101 is clipped at a certain level or more during the signal period, so that the signal is not detected during the no-signal period. and a calculation means 107 that subtracts the noise obtained by the noise extraction means 105 from the output signal of the solid-state imaging device 101.

[0013]

According to the above configuration, the solid-state image sensor 101 outputs a signal having a no-signal period and a signal period for each pixel. The bias adding means 103 applies uniform bias light to the imaging region of the solid-state image sensor 101, or applies bias charges to the signal period of the output signal, thereby increasing the signal level during the signal period. This is so that the influence of the signal during the signal period can be ignored when noise is extracted in the next stage.

Next, the noise extraction means 105 extracts only noise from the output signal from the solid-state image pickup device 101 by clipping a certain level or more from the signal in the signal period. This is equivalent to a signal consisting only of noise during a no-signal period because the signal level during the signal period becomes constant due to clipping.

Further, the calculation means 107 removes and suppresses the noise from the output signal from the solid-state image sensor 101 by subtracting the extracted noise from the signal from the solid-state image sensor 101.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of an imaging apparatus according to the present invention.

In FIG. 2, the CCD element 1 has an imaging area 3 that converts incident light into charges. Also, C
The CD element 1 is equipped with a horizontal transfer CCD register 5 and an output amplifier 7, and the horizontal transfer CCD register 5 takes out the charge generated in the imaging area 3, and the output amplifier 7 amplifies the charge, which can then be output. ing. This output amplifier 7 is constructed using a floating diffusion method.

In the imaging area 3, a bias adding means 1 is provided.
03, bias light 9 for removing reset noise is always incident, thereby making the signal level during the signal period higher than the normal level. Note that other configurations of the bias adding means 103 include horizontal transfer CC
The DC voltage V may be applied to a diode (not shown) placed at the end opposite to the output side of the D register 5. This also makes it possible to increase the signal level during the signal period.

The output of the output amplifier 7 is distributed by a distributor 11. One output of the distributor 11 is sent to the calculation means 107
The (+) input terminal of the subtracter 13 is supplied as one output, and the other output is supplied to the input terminal of the amplifier 15, respectively. The signal input to the amplifier 15 is amplified and then guided to the first clip circuit 17.

The first clipping circuit 17 clips the input signal below the clip level L1, and then clips the input signal to the second clipping circuit 17.
It leads to the clip circuit 19. In the second clip circuit 19,
Clip the input reset signal above the clip level L2. This clipped signal is transferred to the delay line 21
After the time is adjusted to the original signal, the gain is adjusted by the gain adjuster 23, and the signal is supplied to the (-) input terminal of the subtracter 13.

The subtracter 13 subtracts the noise obtained by the gain adjuster 23 from the output signal of the divider 11, so that
Noise in the output signal of the CCD element 1 is suppressed. The output signal of the subtracter 13 has unnecessary components removed by a low pass filter (LPF) 25, and the signal is interpolated and then supplied to the next stage.

The operation of this embodiment configured as described above will be explained below.

FIGS. 3 and 4 are signal diagrams of one embodiment of the present invention.

In the figure, symbols N1, N2, . . . indicate noise levels, symbols S1, S2, . . . signal periods, and symbols BS1, BS2, . . . indicate bias charge signals. Also, the signals in the signal period are (S1 ±N1), (
S2 ±N2),...

In this embodiment, the noise can be removed by extracting the signal in the field-through period 503 where there is no signal and subtracting the noise (±Ni) from the level (Si±Ni) of the signal period. This is how it was done. Note that i represents an arbitrary number.

First, in this embodiment, uniform and constant light is always applied to the imaging area 3 as bias light 9. As a result, the signal waveform output from the CCD element 1 is divided by the bias charge (signals BS1, BS
2,...), the signal level in the signal period 505 increases.

As mentioned above, in order to increase the signal level of the signal period 505, the horizontal transfer CCD register 5
A direct current voltage V may be applied to a diode (not shown) disposed at the end opposite to the output side.

The signal output from the CCD element 1 is divided by a distributor 11, and one signal is supplied to the input terminal of a subtracter 13. The other signal from the distributor 11 is amplified by the amplifier 15 and then input to the first clip circuit 17 . As shown in FIG. 3, the signal level of this signal increases toward the bottom in the figure. Therefore, the first clipping circuit 17 clips the waveform of the signal in the signal period 505, which is lower than the clip level L1, among the input signals. The signal clipped in this way is
The signal is input to the clip circuit 19.

The second clipping circuit 19 also clips the reset period 501 of the input signal which is equal to or higher than a certain level L2. Here, the clipping by the second clipping circuit 19 is for keeping the clipped signal within the dynamic range of the subsequent electric circuit, and is not necessarily necessary depending on the signal level and the dynamic range of the next stage.

The signal obtained in this way has a noise Ni in the field-through period 503 and a noise Ni in the signal period 505.
The bias charge signal BSi (not all) includes a signal due to the reset during the reset period 501. but,
In this clipped signal, the bias charge signal BSi
Since the signal due to the reset does not change, the noise N
This is equivalent to extracting i itself.

The signal thus extracted is delayed in the delay line 21. Thereby, the field-through period 503 of the extracted signal matches the signal period 505 of the original signal. The signal delayed by the delay line 21 is supplied to the gain adjuster 23. In the gain adjuster 23,
After matching the level with the noise in the signal period, the signal is supplied to the subtracter 13. In the subtracter 13, the original signal of the CCD element 1 (
The noise Ni obtained by the gain adjuster 23 is subtracted from the signal in the signal period 505. This means that noise has been removed from the output signal of the CCD element 1. The output signal from the subtracter 13 is interpolated with a reset period and a field-through period by an LPF 25, and is output as an output signal. This output signal can be sent to the next stage, a processing section of a normal camera, to obtain a video signal.

As explained above, according to this embodiment, a no-signal period 503 and a signal period 5 are provided in a period corresponding to one pixel.
05 and the same noise in both periods 503 and 505, to remove the noise without using the correlated double sampling method, CCS method, etc., that is, without requiring a high-speed pulse signal. I can do it.

Note that the LPF 25 of this embodiment has a subtracter 1
3, but it may be provided at the input section of the subtracter 13, respectively. In addition, the subtracter 13
7 is constructed, however, it may be constructed with an adder as long as the sign of the input signal is adjusted.

Further, in this embodiment, the solid-state image sensor 1 is
Although it is constructed using a CD element, it is not limited to this. For example, if an element outputs a signal that has a signal period and a no-signal period (there may be no reset period) as shown in FIG. 3, and the same noise exists in both periods,
The present invention can be applied.

[0036]

As explained above, according to the present invention, when there is a no-signal period and a signal period in a period corresponding to one pixel, and the same noise is present in both periods, a high-speed pulse signal is required. This has the effect of being able to remove the noise without having to do so.

Furthermore, according to the present invention, the circuit configuration can be simplified and power consumption can be reduced. In particular, in high-definition, etc., the above-mentioned correlated double sampling and CCS
However, according to the present invention, the scope of application becomes wider as high-precision television devices such as high-definition television devices are used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention.

FIG. 2 is a configuration diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an output waveform of a CCD element when a bias voltage is applied.

FIG. 4 is an explanatory diagram schematically showing noise separated from a CCD element.

FIG. 5 is a diagram for explaining a noise generation mechanism.

[Explanation of symbols]

1 CCD element (solid-state image sensor) 3 Imaging area 5 Horizontal transfer CCD register 7 Output amplifier 9 Bias light (bias addition means) 11 Distributor 13. Subtractor (calculating means) 15 Amplifier 17 First clip circuit 19 Second clip circuit 21 Delay line 23 Gain adjuster

Claims (1)

[Claims] 1. A solid-state imaging device that outputs a signal that has a no-signal period and a signal period in a period corresponding to a pixel and has the same noise in both periods, and a uniform bias light applied to an imaging area of the solid-state imaging device. or a biasing means for increasing the signal level by applying a bias charge to the signal period of the output signal; and a bias adding means for increasing the signal level by applying a bias charge to the signal period of the output signal; An imaging device comprising: noise extraction means for extracting period noise; and calculation means for subtracting the noise obtained by the noise extraction means from the output signal of the solid-state imaging device.