JP2004165913A - Solid-state imaging unit and its signal reading method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain proper picture quality even for a subject which is moving by suppressing random noise without making a high-speed read repeatedly by a nondestructive read type pixel circuit. <P>SOLUTION: A solid-state imaging unit is provided with two output circuits 4A and 4B which read signals out of one pixel array part through different paths are provided. Two video signals outputted by the output circuits 4A and 4B are processed by addition and averaging to remove random noise. The signals are read by the two output circuits 4A and 4B in the same timing to suppress random noise included in each output system. Further, the two output circuits 4A and 4B are made different in readout timing and then signals of pixels are sequentially outputted at different time from the output circuits 4A and 4B and processed to suppress the random noise included in respective pixels. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid-state imaging device such as a CMOS image sensor and a signal reading method thereof, and more particularly to a configuration for removing random noise from a video signal.
[0002]
[Prior art]
In a conventional CMOS image sensor, a so-called active pixel circuit in which a charge detection amplifier is provided for each pixel is applied, and nondestructive readout is made possible. Is known (for example, see Non-Patent Document 1).
[0003]
[Non-patent document 1]
The Institute of Electronics, Information and Communication Engineers IEICE, ICD2001-88 (2001-09)
[0004]
[Problems to be solved by the invention]
However, in the method of obtaining the random noise suppression effect by oversampling the pixel signal as described above, the readout rate of the pixel signal increases, so that the bandwidth of the readout circuit must be increased, and the random noise of the readout circuit is rather reduced. There is a problem that the effective effect cannot be obtained.
Further, since reading is performed many times, a non-destructive read pixel is actually required from the viewpoint of securing sensitivity. There is also a problem that it cannot be applied to a generally used destructive readout pixel circuit composed of one photodiode and four MOS transistors.
Further, regarding a destructive readout pixel circuit, there is also known a pixel circuit in which imaging and reading are performed a plurality of times at a high speed (several tens of fps or more) and their outputs are averaged to obtain a noise suppression effect.
However, in this case, since a plurality of temporally different images are averaged, it is not suitable for photographing a moving subject.
[0005]
Accordingly, it is an object of the present invention to obtain an effect of suppressing random noise without performing high-speed readout a plurality of times with a non-destructive readout type pixel circuit, and to obtain an appropriate image quality even for a moving subject. An object of the present invention is to provide a solid-state imaging device and a signal reading method thereof.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a pixel array section in which a plurality of pixels including a photoelectric conversion element and a pixel transistor are provided in a two-dimensional array, and the same video signal generated in the pixel array section is transmitted through different paths. It has a plurality of output circuits for reading and outputting, and a signal processing circuit for performing signal processing including random noise removal using a plurality of video signals output from the plurality of output circuits.
[0007]
Further, according to the present invention, there is provided a solid-state imaging device including: a pixel array unit in which a plurality of pixels including a photoelectric conversion element and a pixel transistor are provided in a two-dimensional array; and an output circuit that reads and outputs a video signal from the pixel array unit. In the signal reading method, the same video signal generated in the pixel array unit is read through different paths, and random noise removal is performed using the plurality of read video signals.
[0008]
In the solid-state imaging device and the signal reading method of the present invention, the same video signal generated in the pixel array unit is read through different paths, and random noise removal is performed using the read video signals. It is possible to remove random noise without performing a high-speed readout a plurality of times with a readout type pixel circuit.
In addition, since random noise removal is performed using the same video signal, an appropriate image quality can be obtained even for a moving subject.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a solid-state imaging device and a signal reading method thereof according to the present invention will be described.
FIG. 1 is a circuit diagram showing a configuration example of a CMOS image sensor according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing pixels of the CMOS image sensor shown in FIG.
As shown in FIG. 1, the CMOS image sensor according to the present embodiment has a pixel array section 1 in which a large number of pixels 1A are arranged in a two-dimensional array, and a vertical (pixel row) direction in which each pixel of the pixel array section 1 is scanned in a vertical (pixel row) direction. A scanning circuit (not shown); a vertical signal line 2 provided for each pixel column of the pixel array section 1; a constant current source 3 for supplying a constant current to each vertical signal line 2; And two horizontal scanning circuits 5A and 5B that sample and hold pixel signals output to the first and second circuits and remove fixed pattern noise, and scan and output each of the output circuits 4A and 4B in the horizontal direction. Having.
[0010]
As shown in FIG. 2, the pixel 1A is provided with a photodiode (PD) 10 as a photoelectric conversion element and four pixel transistors (Tr) 11, 12, 13, and 14 for transfer, amplification, selection, and reset. It constitutes a pixel circuit.
The PD 10 stores the electrons generated by the photoelectric conversion. The transfer Tr 11 transfers the electrons of the PD 10 to the floating diffusion (FD) 15 based on the transfer pulse ΦTXm from the vertical scanning circuit.
The gate of the amplification Tr12 is connected to the FD15, and converts the fluctuation in the potential of the FD15 into an electric signal. The selection Tr13 selects a pixel from which a signal is to be read out on a row basis based on a row selection pulse ΦSELm from the vertical scanning circuit.
The reset Tr14 resets the potential of the FD 15 to Vdd based on the transfer pulse ΦRSTm from the vertical scanning circuit.
The configuration of the pixel circuit is not limited to the illustrated one, but may be a three-transistor configuration, for example.
[0011]
The output circuits 4A and 4B have the same circuit configuration provided on both sides of the vertical signal line 2, read out and output the same video signal photographed by the pixel array unit 1, and output A column signal processing unit that samples and holds a pixel signal is provided for each signal line 2. Since the output circuits 4A and 4B have a common configuration, common components will be described collectively using the same reference numerals.
The column signal processing unit used in this example includes a CDS (correlated double sampling) circuit that removes noise by calculating a difference between a reset level and a signal level of each pixel, and includes a clamp capacitor 61 and a clamp switch. 62, a sample and hold switch 63, a sample and hold capacitor 64, an output amplifier 65, and an output selection switch 66.
[0012]
The clamp capacitor 61 sequentially inputs a reset level sample signal and a signal level sample signal of each pixel through the vertical signal line 2.
The clamp switch 62 is controlled by clamp pulses ΦCLP1 and ΦCLP2 from a timing generator (not shown), and changes the output of the clamp capacitor 61 to a predetermined clamp voltage level Vclp when a reset level sample signal is input to the clamp capacitor 61. It is to clamp.
[0013]
That is, when the output side of the clamping capacitor 61 is clamped to the clamp voltage level Vclp by the clamp switch 62, the input side and the output side of the clamping capacitor 61 are held at different potentials. When a sample signal of a signal level is input to the input terminal, a potential change on the input side causes a potential change on the output side, and this potential change is sampled and held by the sample and hold switch 63 and the sample and hold capacitor 64. I have.
The sample-and-hold switch 63 changes the output value of the clamping capacitor 61 based on the sample-and-hold pulses ΦSH1 and ΦSH2 and outputs the output value of the clamping capacitor 61 when the sample signal of the signal level is input to the clamping capacitor 61 after being clamped by the clamp switch 62. The sample-and-hold capacitor 64 holds the output value of the clamp capacitor 61.
[0014]
The output selection switch 66 sequentially outputs the sample signal value of the sample-and-hold capacitor 64 to the output amplifier section 65 through the horizontal signal line 7, and is controlled by horizontal synchronization pulses ΦHSWn from the horizontal scanning circuits 5A and 5B.
The output amplifier section 65 is obtained by inserting a parallel circuit of a capacitor 65B and a reset switch 65C into a negative feedback loop of an operational amplifier 65A. The discharge signal from the sample-and-hold capacitor 64 output based on the horizontal synchronization pulse is converted into a waveform by the capacitor 65B, and the video signal is output while the opening and closing of the discharge signal is controlled by the reset switch 65C by the reset pulse ΦOPRSTn corresponding to the horizontal synchronization pulse ΦHSWn. I do.
[0015]
In the CMOS image sensor having the above-described configuration, two video signals output from the two output circuits 4A and 4B that read signals from one pixel array unit 1 through different paths are A / D-converted by the subsequent signal processing circuit. After conversion and input to a DSP (Digital Signal Processor), and processing such as averaging of two video signals is performed, random noise is removed. Note that the subsequent signal processing circuit may be provided on the same chip as the image sensor, or may be provided outside the chip.
[0016]
FIG. 3 is a timing chart showing a first operation example of the CMOS image sensor shown in FIG. 1, and FIG. 4 is a timing chart showing a second operation example.
In the example shown in FIG. 3, signals are read out at the same timing by the two output circuits 4A and 4B, and the clamp pulses ΦCLP1 and ΦCLP2 and the sample hold pulses ΦSH1 and ΦSH2 of the output circuits 4A and 4B are the same. It's time.
As a result, the signals of the same pixel are sequentially output from the output circuits 4A and 4B, and by processing this signal, it is possible to suppress random noise included in each output system.
[0017]
On the other hand, in the example shown in FIG. 4, the read timings of the two output circuits 4A and 4B are slightly shifted, and the clamp pulses ΦCLP1 and ΦCLP2 and the sample hold pulses ΦSH1 and ΦSH2 of the output circuits 4A and 4B are several pixels. The timing is slightly off.
In this way, by sampling signals from the pixel circuits at the output circuits 4A and 4B at different timings, uncorrelated noise is sampled at different times in the output circuits 4A and 4B. By processing this, it is possible to suppress the random noise included in each pixel in addition to the random noise included in each output system.
[0018]
Although the above example describes a configuration in which two output circuits are provided, it is also possible to provide three or more output circuits so as to obtain three or more identical video signals.
Although the above-described output circuit has been described with respect to a configuration example in which pixel signals are clamped and held, the present invention is not limited to this, and various modes can be selected. A circuit that distributes the level to two capacitors provided in parallel and takes a difference may be used.
In addition, the signal processing at the subsequent stage from the output circuits 4A and 4B may be performed by appropriately selecting a timing, and is not restricted by the read timing shown in FIGS.
[0019]
【The invention's effect】
As described above, in the solid-state imaging device and the signal reading method of the present invention, the same video signal generated in the pixel array unit is read through different paths, and random noise removal is performed using the read video signals. Therefore, there is an effect that random noise can be removed without performing high-speed readout a plurality of times by a non-destructive readout pixel circuit, and an appropriate image quality can be obtained even for a moving subject.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration example of a CMOS image sensor according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a pixel of the CMOS image sensor shown in FIG.
FIG. 3 is a timing chart showing a first operation example of the CMOS image sensor shown in FIG.
FIG. 4 is a timing chart showing a second operation example of the CMOS image sensor shown in FIG.
[Explanation of symbols]
1 ... pixel array section, 1A ... pixel, 2 ... vertical signal line, 3 ... constant current source, 4A, 4B ... output circuit, 5A, 5B ... horizontal scanning circuit, 7 ... horizontal signal line, 10 Photodiode, 11 Transfer transistor, 12 Amplification transistor, 13 Selection transistor, 14 Reset transistor, 15 Floating diffusion, 61 Capacitor for clamping, 62 Clamp switch, 63 ... Sample-and-hold switch, 64... Sample-and-hold capacitor, 65... Output amplifier section, 66.

Claims (12)

A pixel array unit in which a plurality of pixels including a photoelectric conversion element and a pixel transistor are provided in a two-dimensional array;
A plurality of output circuits for reading and outputting the same video signal generated by the pixel array unit through different paths,
A signal processing circuit that performs signal processing including random noise removal using a plurality of video signals output by the plurality of output circuits,
A solid-state imaging device comprising: The solid-state imaging device according to claim 1, wherein the output circuit includes a fixed pattern noise removing unit that removes fixed pattern noise of the video signal. 2. The solid-state imaging device according to claim 1, wherein the output circuit reads the video signal from the pixel array unit at the same read timing for each output circuit. 2. The solid-state imaging device according to claim 1, wherein the output circuit reads the video signal from the pixel array unit at a different read timing for each output circuit. The solid-state imaging device according to claim 1, wherein the signal processing circuit removes random noise by taking an average of a plurality of video signals output from the plurality of output circuits. Each pixel of the pixel array unit includes an amplification transistor that detects a signal charge generated by the photoelectric conversion element and outputs a pixel signal; a selection transistor that connects an output of the amplification transistor to an output signal line; The solid-state imaging device according to claim 1, further comprising: a reset transistor that resets a signal charge output from the conversion element to the amplification transistor. The solid-state imaging device according to claim 6, wherein each pixel of the pixel array unit further includes a transfer transistor that supplies a signal charge generated by the photoelectric conversion element to the amplification transistor. A signal reading method for a solid-state imaging device, comprising: a pixel array unit in which a plurality of pixels including a photoelectric conversion element and a pixel transistor are provided in a two-dimensional array; and an output circuit that reads and outputs a video signal from the pixel array unit. hand,
The same video signal generated in the pixel array unit is read through different paths, and random noise removal is performed using the plurality of read video signals.
A signal reading method for a solid-state imaging device. 9. The signal reading method for a solid-state imaging device according to claim 8, wherein, when reading a plurality of video signals from the pixel array unit, fixed pattern noise of each video signal is removed. 9. The signal reading method for a solid-state imaging device according to claim 8, wherein when reading the video signal from the pixel array unit, the reading is performed at the same read timing for each video signal. 9. The signal reading method for a solid-state imaging device according to claim 8, wherein when reading the video signal from the pixel array unit, the reading is performed at a different read timing for each video signal. 9. The method according to claim 8, wherein random noise is removed by averaging the plurality of video signals.

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