JP2510501B2 - Solid-state imaging device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid-state image pickup device using a solid-state image pickup element used as a television camera or the like.

[Background of the Invention]

A MOS type solid-state image pickup device composed of a pixel array of a solid-state image pickup device composed of a photoelectric conversion element and a switch element and a scanning circuit for sequentially extracting the signal charges accumulated in each pixel in time series is When strong light is incident on a part, false signals called blooming and smear that generate bright lines above and below the light spot on the reproduction screen are generated. In order to remove such a false signal, especially smear, the smear charge accumulated in the signal line is discharged by the reset operation as disclosed in Japanese Patent Laid-Open No. 59-1442778. However, the above publication does not disclose how to apply the reset voltage when the signal readout preamplifier is a feedback type often used in a MOS type image pickup device, and the reset voltage and the open-end voltage of the preamplifier are not disclosed. However, there is a problem that an undesired transient response waveform is mixed in the signal waveform first read after the smear is discharged.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned problems of the prior art, and when reading the signal charge accumulated in the pixel by the feedback type preamplifier, the open input DC voltage of the feedback type preamplifier and the reset voltage are made to coincide with each other, and a smear is performed. (EN) It is possible to provide a solid-state imaging device that eliminates the influence of a transient response that occurs after ejection.

[Outline of Invention]

To achieve this object, the present invention is characterized in that the output voltage of the feedback type preamplifier for reading out the signal charge accumulated in the pixel is the reset voltage of the signal line.

Example of Invention

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

FIG. 1 is a configuration diagram (a) showing a first embodiment of a solid-state image pickup device according to the present invention and a time chart (b) showing the driving pulse timing thereof, where 1 is a MOS type solid-state image pickup element and 2 is a preamplifier. 3 is a feedback resistor of a preamplifier, 4 is an output terminal, 10 is a vertical scanning circuit, 11 and 12 are vertical scanning circuit output lines (vertical gate lines), 20 is a horizontal scanning circuit, and 21 and 22 are horizontal scanning circuit output lines ( Horizontal gate line), 31 to 34 are photodiodes (photoelectric conversion elements), 41 to 44 are vertical MOS transistors, 51 to 54 are horizontal MOS transistors, 61 and 62 are line selection MOS transistors, 71 and 72 are reset MOS transistors, 81 and 82 are horizontal signal lines, 91 is a vertical signal line, 101 is a video signal output terminal, 102 is a reset terminal, and 103 is a reset pulse application terminal. In the figure, although many photodiodes, gate lines, and signal lines are actually arranged,
In the figure, only one part is shown for the sake of explanation.

In the same figure, the reset pulse is applied to the reset pulse applying terminal 103 at the timing shown in the time chart (b) prior to the horizontal scanning pulse.
The MOS transistors 1 and 72 are turned on and the smear charges accumulated in the horizontal signal lines 81 and 82 are discharged through the reset terminal 102, and at the same time, the potentials of the horizontal signal lines 81 and 82 are reset to the reset voltage. Then, a vertical gate pulse is output from the vertical scanning circuit 10 to the vertical gate line 11. As a result, the vertical MOS transistors 41, 42 are turned on. Furthermore, when horizontal gate pulses are sequentially output from the horizontal scanning circuit 20 to the horizontal gate lines 21 and 22, the horizontal MOS transistors 51 and 52 are sequentially turned on and the signal charges accumulated in the photodiodes 31 and 32 of the first row are stored. Are sequentially read out to the horizontal signal line 81, and the line selection MOS transistor 61, the vertical signal line 91, and the signal output terminal 101.
Is output via. Also in the next 1H (1 horizontal scanning period), first, the reset pulse is applied again within the H.BLK (horizontal blanking) period, the smear charge is discharged in the same manner as described above, and then the photo of the next row is performed. Read out the signal charge of the diode. Thereafter, by repeating this operation, the accumulated signal charges of all the photodiodes are read out, and a video signal is obtained at the output terminal 4 of the feedback type preamplifier (comprising the preamplifier 2 and the feedback resistor 3) connected to the signal output terminal 101. .

By the way, the feedback preamplifier is a polarity reversal type voltage amplifier having a high input impedance and a high gain provided with a feedback resistor.However, this circuit has a DC input / output when the input is open to DC. Feedback is applied so that the voltages match and balanced at a certain voltage Vi. This voltage Vi is the open input DC voltage of the feedback preamplifier. When the voltage applied to the reset terminal 102 in FIG. 1 (a) is V _R , the potential of the horizontal signal line after discharging the smear charge is
It is reset to V _R. After resetting, until the line selection MOS transistor is turned on, the horizontal signal line is not connected to anything, so that the signal line acts as a capacitor C _H (that is, capacitance, not shown). Then, the voltage V _R at the time of the reset is held. When the line selection MOS transistor is turned on, a transient current equivalent to that when the capacitor C _H charged to the voltage V _R is connected to the input of the feedback type preamplifier flows. The magnitude of the transient current, reset voltage V difference between the open input DC voltage Vi of _R and a preamplifier (V _R -Vi) and mobile charge amount Q _T represented by the product of the capacitance value C _H of the horizontal signal line Can be evaluated with. Compare this with the amount of signal charge Q _S that can be stored to the maximum in one photodiode. The capacitance value of the capacitor C _H is about 3 pF, the capacitance value of the photodiode is about 0.03 pF, and the bias voltage of the photodiode is about 1 V. Therefore, taking the case where the difference between V _R and Vi is 0.1 V as follows, Like

Q _T = 0.1V × 3pF = 0.3pq (pico coulomb) Q _S = 1V × 0.03pF = 0.03pq From this, it can be seen that a transient current about 10 times larger than the maximum signal flows. This transient current flows only in the beginning portion of the video period (the left end portion of the reproduced screen) by horizontal scanning, but its peak value is large, so that the tailing of the response disturbs the image. In particular, in a camera that uses the black level as a reference, which is called an optical black, there is a problem that an error occurs in the black level of the entire screen. For these reasons, the need for it allowed to coincide as much as possible the voltage Vi and the voltage V _R will be described.

In this regard, in the first embodiment of the present invention, as shown in FIG. 1, the output voltage of the feedback type preamplifier is supplied to the reset terminal 102 as the reset voltage to satisfy the above requirement.

As described above, the feedback preamplifier has the same input / output voltage when the input terminal is open, and, as can be seen from the time chart shown in FIG. 1 (b), the reset MOS transistor. At the timing when 71 and 72 are turned on and the reset voltage is actually applied to the horizontal signal line, the line selection MOS transistor is just turned off and the input terminal of the feedback type preamplifier is practically open. The application of the preamplifier output voltage as the reset voltage to the reset terminal is nothing but the matching of the voltages V _R -Vi. The voltage
If only V _R and Vi are to be matched, the preamplifier input voltage may be used as the reset voltage directly or via a buffer such as a voltage follower, but in the camera that uses the MOS image sensor and the feedback preamplifier, This method is not suitable because adding an extra circuit to the input terminal of the preamplifier significantly increases noise.

FIG. 2 is a block diagram showing a second embodiment of the solid-state image pickup device according to the present invention, in which the same symbols as in FIG. 1 indicate the same parts, 5 is a voltage follower, 6 is a resistor, and 7 is a capacitor. ,
A resistor 6 and a capacitor 7 form a low pass filter.

In the figure, the output voltage of the preamplifier 2 is passed through a low-pass filter to remove high frequency noise, and then applied as a reset voltage to the reset terminal 102 of the MOS type image sensor 1.
According to this structure, the reset voltage is less likely to be affected by spike noise or high frequency random noise.

FIG. 3 is a block diagram showing a third embodiment of the solid-state image pickup device according to the present invention, in which the same symbols as in FIG. 1 indicate the same parts, 5 is a voltage follower, 7 is a capacitor, 8 is a MOS transistor, Reference numeral 9 denotes a sampling pulse application terminal, which constitutes a sample hold circuit with the capacitor 7 and a MOS transistor.

In the figure, a voltage equal to the open input DC voltage of the preamplifier 2 is applied by applying to the terminal 9 a sampling pulse generated in an appropriate period when none of the line selection MOS transistors in the MOS type image sensor 1 is turned on. The sample is held and applied to the reset terminal 102 via the voltage follower 5. According to this configuration, since the line selection MOS transistor does not necessarily have to be turned off at the time of reset, there is an effect that the degree of freedom in circuit design is increased.

FIG. 4 is a block diagram showing a fourth embodiment of the solid-state image pickup device of the present invention. The same reference numerals as those in FIGS. 1 and 3 denote the same parts, 200 is a comparator, and E is a fixed voltage. .

In the figure, the sample hold circuit composed of the capacitor 7 and the MOS transistor 8 samples and holds a voltage equal to the open input DC voltage Vi of the preamplifier at the same timing as that of the embodiment shown in FIG. A fixed voltage E is applied to the reset terminal 102, the difference between the sampled and held voltage Vi and the reset voltage is detected by the comparator 200, and the bias circuit of the preamplifier 2 is automatically controlled so as to minimize the difference.

FIG. 5 is a block diagram showing a fifth embodiment of the solid-state image pickup device according to the present invention. The same reference numerals as those in FIGS. 1 and 4 denote the same parts, 77 is a second capacitor, and 88 is a second capacitor. The second MOS transistor 99 is a second sampling pulse applying terminal, and the second capacitor 77 and the second MOS transistor 88 form a second sample and hold circuit.

In the figure, the second sample-hold circuit applies a sampling pulse to the terminal 99 at a timing immediately after the line selection MOS transistor (FIG. 1) is turned on to sample-hold the output voltage of the preamplifier 2. As a result, the voltage at the peak of the undesirable transient response waveform is detected. Similar to the third embodiment, the sample and hold circuit composed of the capacitor 7 and the MOS transistor 8 detects a voltage which is effectively equal to the open input DC voltage of the preamplifier 2 or a black level signal corresponding to the optical black. To do. The comparator 200 automatically controls the reset voltage so as to minimize the voltage difference between the two. That is,
The transient response which is a problem in the present invention is minimized.

As described above, the present invention achieves the above-mentioned object of the present invention by making the reset voltage and the open input DC voltage of the preamplifier coincide with each other, as is apparent from each embodiment.

In the above description, the solid-state image pickup device is of a type that scans one line at a time, but the present invention is not limited to this, and the solid-state image pickup device described in the publication cited as the conventional example is not limited to this. It is obvious that the present invention can also be applied to the type of scanning rows simultaneously.

〔The invention's effect〕

As described above, according to the present invention, the reset voltage of the solid-state image sensor and the open input DC voltage of the preamplifier for reading the video signal are automatically matched or the difference between the two is minimized, so that after smear discharge. An undesired transient response waveform generated in the signal waveform read first can be suppressed to a minute level, and a solid-state imaging device having an excellent function can be provided excluding the above-mentioned drawbacks of the related art.

[Brief description of drawings]

FIG. 1 is a configuration diagram (a) showing a first embodiment of a solid-state image pickup device according to the present invention and a time chart showing its drive pulse timing, and FIGS. 2 to 5 are second diagrams of the solid-state image pickup device according to the present invention. 5 is a configuration diagram showing a fifth embodiment. FIG. 1 ... MOS solid-state image sensor, 2 ... preamplifier, 4 ...
Output terminal, 10 ... vertical scanning circuit, 20 ... horizontal scanning circuit,
31-34 …… Photodiode, 41-44 …… Vertical MOS transistor, 51-54 …… Horizontal MOS transistor, 61, 62 ……
Line selection MOS transistor, 71,72 ... Reset MOS transistor, 81,82 ... Horizontal signal line, 91 ... Vertical signal line, 101 ... Video signal output terminal, 102 ... Reset terminal,
103 ...... Reset pulse application terminal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiro Kinugasa, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi Home Appliance Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-59-132162 (JP, A)

Claims (5)

(57) [Claims] 1. A pixel array composed of a plurality of photoelectric conversion elements arranged in a matrix, and a vertical gate line for each row of the arrangement of the photoelectric conversion elements of the pixel array, and one vertical gate line is provided in order. A vertical scanning circuit that outputs a vertical gate pulse for each horizontal scanning period, and a horizontal gate line for each column of the array of the photoelectric conversion elements of the pixel array, and a horizontal gate pulse is sequentially applied to the horizontal gate line for each horizontal scanning period. And a signal line for each row of the array of photoelectric conversion elements of the pixel array, and each photoelectric conversion element outputs from the vertical scanning circuit to the vertical gate line. A first switch element which is driven by a vertical gate pulse to be turned on and is turned on is connected, and the first switch element is driven by the horizontal gate pulse output from the horizontal scanning circuit to the horizontal gate line. By a vertical gate pulse which is connected to the signal line of the corresponding row via the second switch element which is turned on and is provided for each signal line, and which is output from the vertical scanning circuit to the vertical gate line. A line selection switch element that is driven to turn on and connects the signal line to a single signal output terminal; a reset switch element that is provided for each signal line and that connects the signal line to a single reset terminal; In a solid-state imaging device having a feedback preamplifier connected to a signal output terminal, means for supplying an output voltage of the feedback preamplifier to the reset terminal is provided, and the reset is performed within a period in which the line selection switch is off. The solid-state imaging device characterized in that the signal line is reset to a voltage equal to the open input voltage of the feedback preamplifier by driving the switch element. Location. 2. The solid-state imaging device according to claim 1, wherein the means directly supplies the output voltage of the feedback preamplifier to the reset terminal. 3. The solid-state imaging device according to claim 1, wherein the means comprises a low-pass filter that smoothes an output voltage of the feedback preamplifier. 4. The solid-state imaging device according to claim 1, wherein the means comprises a sample hold circuit. 5. A pixel array composed of a plurality of photoelectric conversion elements arranged in a matrix, and a vertical gate line for each row of the arrangement of the photoelectric conversion elements of the pixel array, and the vertical gate lines are sequentially provided with 1 A vertical scanning circuit that outputs a vertical gate pulse for each horizontal scanning period, and a horizontal gate line for each column of the array of the photoelectric conversion elements of the pixel array, and a horizontal gate pulse is sequentially applied to the horizontal gate line for each horizontal scanning period. And a signal line for each row of the array of photoelectric conversion elements of the pixel array, and each photoelectric conversion element outputs from the vertical scanning circuit to the vertical gate line. A first switch element which is driven by a vertical gate pulse to be turned on and is turned on is connected, and the first switch element is driven by the horizontal gate pulse output from the horizontal scanning circuit to the horizontal gate line. By a vertical gate pulse which is connected to the signal line of the corresponding row via the second switch element which is turned on and is provided for each signal line, and which is output from the vertical scanning circuit to the vertical gate line. A line selection switch element that is driven to turn on and connects the signal line to a single signal output terminal; a reset switch element that is provided for each signal line and that connects the signal line to a single reset terminal; In a solid-state imaging device having a feedback preamplifier connected to a signal output terminal, means for supplying a constant voltage to the reset terminal and the feedback preamplifier at a timing within a period in which the line selection switch element is off. A sample and hold circuit that samples and holds the output voltage of the feedback preamplifier that is equal to the open input terminal voltage of the A voltage comparator that detects a difference voltage from the output voltage of the line and controls the open input terminal voltage of the feedback type preamplifier according to the difference voltage. A solid-state image pickup device, characterized in that when the reset switch element is turned on, the signal line is reset to the constant voltage and the open input terminal voltage of the feedback preamplifier is set equal to the constant voltage.