JPH088665B2 - Driving method for solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a method for driving a two-dimensional solid-state imaging device, and is particularly used for a sensor for a television camera.

(Prior Art) FIG. 3 is a layout diagram showing a general configuration of a two-dimensional solid-state imaging device. Generally, a two-dimensional solid-state image pickup device is constructed on a semiconductor substrate, and light receiving and accumulating portions 1 for accumulating signal charges obtained by photoelectrically converting incident light are arranged in two dimensions of x and y. A vertical charge transfer section 2 is arranged adjacent to the column of the light receiving and accumulating section 1 in the y direction, and the signal charges transferred from the light receiving and accumulating section 1 are transferred to the vertical charge transfer section 2. Further, an image memory 3 for temporarily accumulating signal charges is provided on the extension of the vertical charge transfer unit 2, and the signal charges transferred from the vertical charge transfer unit 1 shown in the figure are inside the image memory 3. Is temporarily stored in. After that, the signal charges are transferred line by line to the horizontal charge transfer unit 4 provided near the lower end of the image memory 3 and then transferred in the x direction to be provided at the end of the horizontal charge transfer unit 4. The output amplifier 5 performs voltage conversion and impedance conversion and outputs.

In such a configuration, the vertical charge transfer unit 2, the image memory 3, and the horizontal charge transfer unit 4 are connected to the charge coupled device (Charge).
It is often composed of a Coupled Device (CCD).

FIG. 4 is a view showing a sectional structure of a portion cut along line XX ′ shown in FIG. A diode type light receiving and accumulating portion is formed by burying a diffusion layer 1a having a conductivity type opposite to that of the semiconductor substrate 6, and the vertical charge transfer portion 2a is a channel diffusion formed on the transfer electrode 7 and the substrate surface thereunder. And layer 8.

As shown in the figure, the transfer electrode 7 also functions as a CCD transfer electrode and a field shift electrode for reading out the signal charges from the light receiving and accumulating portion 1a. Since the voltage of the pulse used for reading the charge from the light receiving / accumulating portion 1a needs to have a larger absolute value than the pulse used for transferring the CCD, the pulse applied to the transfer electrode 7 is necessarily a three-level pulse.

FIG. 5 is a waveform diagram showing an example of such a pulse applied to the transfer electrode 7. FIG. 5 (a) shows a composite blanking pulse, which is composed of one short horizontal 1 horizontal period (referred to as 1H) 9 and a long repeated one vertical period (referred to as 1V), and is used to reproduce television. On the screen, each corresponds to one horizontal scanning line and one screen. Here, one horizontal period 9 is composed of a horizontal blanking period 11 and a horizontal valid period 12, and a vertical blanking period 13 which is an invalid period exists in one vertical period 10.

5 (b) and 5 (c) show the transfer pulse applied to the vertical charge transfer unit 2 shown in FIG. 3 as φ _vi (i is an integer), and the pulse applied to the image memory 3 as φ _sj (j is the integer). FIG. 6 is a waveform diagram showing an example of those when (integer). Vertical charge transfer unit 2
Since the image memory 3 is often composed of a CCD controlled by four-phase drive transfer pulses, i = 1, 2,
Although 3, 4 and j = 1, 2, 3, and 4, each of which is composed of four transfer pulses, only one pulse waveform of each is shown here. The pulse φ _vi applied to the vertical charge transfer unit 4 is stopped during the vertical effective period as shown in FIG.
It is composed of a field shift pulse 14 and a field transfer pulse 15 following it. Vertical blanking period
In 13 first, a field shift pulse 14 is applied in order to read out signal charges from the light receiving / accumulating portion 1 to the vertical charge transfer portion 2. Then, a field transfer pulse 15 for transferring the signal charges in the vertical charge transfer section 2 to the image memory 3 is applied.

The pulse φ _sj applied to the image memory 3 is shown in FIG. 5 (c).
As shown in, the field transfer pulse 15a for receiving the signal charge sent from the vertical charge transfer unit 2 in the vertical blanking period 13 and the horizontal transfer by inserting each line in the horizontal blanking period 11 Line shift pulses 16-1, 16-2, 16- for sequentially transferring signal charges to the section 4
It consists of 3, ... The signal charges transferred to the horizontal transfer unit 4 are sequentially transferred within the horizontal effective period 12 and are amplified and output by the output amplifier 5.

FIG. 6 is an input / output characteristic diagram showing the relationship between the input light quantity of the light receiving and accumulating section and its output. As is clear from the figure, when the amount of incident light increases, the output increases in proportion to it, but the output characteristic has a saturation level S, and when it reaches this level, the output becomes constant regardless of the amount of incident light.

(Problems to be Solved by the Invention) The ratio L _S / L _N between the incident light amount L _S corresponding to the saturation level S and the incident light amount L _N corresponding to the output noise level N is called the dynamic range. The solid-state imaging device has a problem that the dynamic range is narrow as shown in FIG. 6 and an image having a wide incident light amount range cannot be obtained.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a driving method of a solid-state imaging device capable of obtaining a large dynamic range of the solid-state imaging device.

[Structure of Invention]

(Means for Solving the Problems) In the present invention, when the signal charge accumulated in the light receiving accumulation section is transferred to the image memory through the vertical charge transfer section and the excess charge is discharged, the vertical blanking period and vertical In a method for driving a solid-state imaging device, which controls transfer using a composite blanking pulse having a blanking period, a field shift discharge pulse that is inserted during a horizontal blanking period and whose amplitude gradually decreases in each horizontal blanking period. The first step of discharging a part of the signal charge from the light receiving and accumulating section to the vertical charge transfer section, and the signal charge discharged into the vertical charge transfer section by this first step was inserted during the vertical blanking period. The second step of sweeping by the charge discharge transfer pulse, and the remaining portion of the signal charge by the field shift pulse in the light receiving and storing section From the vertical charge transfer unit to the image memory by the third step of transferring from the vertical charge transfer unit to the image memory by a field delivery pulse. And a step are provided.

(Operation) In the driving method according to the present invention, a part of the signal charge accumulated in the light receiving and accumulating portion is discharged a plurality of times during the horizontal blanking period prior to the charge transfer. As a result, in the case of bright light, since the charges are accumulated while discharging the excess charges, the saturated light amount L _S becomes large. Further, since the discharge pulse is used to discharge the excess electric charge similarly to the read pulse, the waveform deformation due to the wiring resistance and the like is the same in the discharge and transfer, so that the variation in the discharge amount for each pixel is reduced, A stable dynamic range can be adjusted.

(Embodiment) An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2. FIG. 1 is a waveform diagram showing drive pulses used in the present invention. At a predetermined timing of the composite blanking pulse shown in FIG. 1 (a), the application pulse φ _vi shown in FIG. 1 (b) is applied to the transfer electrode of the vertical charge transfer unit, and as shown in FIG. 1 (c). The applied pulse φ _sj shown is applied to the transfer electrodes of the image memory 3.

The transfer pulse φ _sj applied to the image memory 3 has the same configuration as the conventional pulse, but the applied pulse φ _vi applied to the vertical charge transfer unit is different from the configuration of the conventional applied pulse. That is, as shown in FIG. 1 (b), a field shift discharge pulse whose amplitude is adjusted within the horizontal blanking period 11 so as to gradually decrease for each blanking period.
17-1, 17-2, 17-3, ... Are provided. Also, within the vertical blanking period 13, the field shift pulse 14
Is provided with a charge discharge transfer pulse 18 preceding. If the pulse-shaped control signal is used as the field shift discharge pulse, if it is simply the voltage level signal, it differs from that in the read pulse of the waveform deformation due to the resistance of the wiring or the substrate. This is because the waveform becomes large, and therefore the waveform deformation is made approximately the same as that of the read pulse.

The charges discharged to the vertical charge transfer section 2 by the charge discharge transfer pulse 18 are normally discharged to the discharge drain 101 provided on the opposite side of the image memory 3 as shown in FIG. It is also possible to discharge it. Field shift discharge pulse 17-1, 17-2, 17-3,
If the pulse is configured such that the voltage envelope 19 of ... Is convex, that is, the rate of change of the amplitude increases with the passage of time, the received light accumulating portion 1 will be rapidly exposed to strong incident light. Since a part of the accumulated charge is discharged by the field shift discharge pulses 17-1, 17-2, 17-3, ..., The saturated output S cannot be reached. On the other hand, when the incident light is weak, the charge is slowly accumulated, so the discharge pulse
It is not discharged by 17-1, 17-2, 17-3, .... Therefore, the same output as before can be obtained for weak incident light,
For strong output, the output will be suppressed.

Transfer of the signal charge after discharging a part of the signal charge by the field shift discharge pulse 17-1, 17-2, 17-3, ... And the charge discharge transfer pulse 18 is performed by the field shift pulse 14, as in the conventional case. This is performed by field transfer pulses 15, 15a, line shift pulses 16-1, 16-2, 16-3, ....

FIG. 2 shows the input / output characteristics of the light receiving / accumulating section when driven by the drive pulse shown in FIG. Since the output is saturated in the part where the amount of incident light is large, the dynamic range becomes L _S ′ / L _N , which is larger than the conventional dynamic range L _S / L _N shown in Fig. 6, and a high dynamic range can be achieved. Becomes

If this input / output characteristic is matched with the gamma (γ) characteristic of the television monitor, it is particularly advantageous in signal processing.

〔The invention's effect〕

As described in detail with reference to the embodiments above, in the present invention, a part of the excess signal charge is discharged using the field shift discharge pulse and the charge discharge transfer pulse before the transfer of the signal electrode, and then the remaining signal charge is discharged. Therefore, the dynamic range of the solid-state imaging device can be expanded. Further, since the field shift discharge pulse is used for discharging excess charges, it is possible to reduce variations in discharge amount due to the influence of wiring and the like.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing an example of a drive transfer pulse used in the driving method of the present invention, and FIG. 2 is a characteristic diagram showing the input / output characteristics of the light receiving and accumulating section when the driving method of the present invention is used Third
FIG. 4 is a layout diagram showing the structure of a solid-state image pickup device used in the present invention, FIG. 4 is a sectional view of a portion cut along line XX 'in FIG. 3, and FIG. 5 is used in a conventional driving method. FIG. 6 is a waveform diagram showing an example of the drive transfer pulse that is used, and FIG. 6 is a characteristic diagram showing the input / output characteristics of the light receiving and accumulating portion when the conventional driving method is adopted. 11 ... horizontal blanking period, 13 ... vertical blanking period, 14 ... field shift pulse, 15, 15a ... field transfer pulse, 16-1, 16-2, 16-3 ... line shift pulse, 17 -1,17-2,17-3 ... Field shift discharge pulse, 18 ... Charge discharge transfer pulse.

Claims (2)

[Claims] 1. A composite blank having a horizontal blanking period and a vertical blanking period when transferring signal charges accumulated in a light receiving and accumulating unit to an image memory through a vertical charge transferring unit and discharging excess charges. In a method of driving a solid-state imaging device that controls transfer using a ranking pulse, part of the signal charge is inserted by a field shift discharge pulse that is inserted during the horizontal blanking period and whose amplitude gradually decreases in each horizontal blanking period. A first step of discharging from the light receiving and accumulating section to the vertical charge transfer section, and a charge discharging operation of inserting the signal charges discharged into the vertical charge transfer section by the first step into the vertical blanking period. The second step of sweeping by the transfer pulse, and the remaining part of the signal charge by the field shift pulse. A third step of transferring from the accumulation section to the vertical charge transfer section, and the remaining portion transferred into the vertical charge transfer section by the third step from the vertical charge transfer section to the image by a field delivery pulse. And a fourth step of transferring to a memory. 2. The method of driving a solid-state image pickup device according to claim 1, wherein the level change rate of the charge discharge transfer pulse inserted in the vertical blanking period changes so as to increase with time. .