JPS6023545B2 - Driving method of solid-state image sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Application of the Invention The present invention relates to a method for driving an image sensor that can expand the light amount range of a MOS group image sensor.

(2) Prior Art FIG. 1 is a diagram showing the configuration of a MOS group image sensor.

Photodiodes 1 arranged in a matrix and a horizontal readout switch 51 for reading out signals accumulated in the photodiodes, . 52, 5m, vertical start switches 61, 62, 6n, a horizontal shift register 2, a vertical shift register 3, and an output signal line 4 for opening and closing the respective switches in an orderly manner. It is composed of horizontal and vertical readout switch MOS type FETs, and the switch operation is performed by controlling the gate voltage with the output pulse of each stage of the horizontal and vertical shift registers.
The signal accumulated in the diode is read out to a load circuit composed of a resistor 7 and a power supply 8. FIG. 2 is a circuit configuration diagram when reading a signal from one photodiode.

The photodiode 1 has a parasitic capacitor 9, and the potential of the capacitor 9 is maintained at the power supply voltage when no light is incident.

When light hits the photodiode 1, a current flows through the diode, gradually neutralizing the accumulated charge in the capacitor 9, and changing the potential of the capacitor 9. When the switching transistors 12 and 10 are turned on by the output pulses of the shift registers 2 and 3, the power supply voltage is again supplied to the capacitor 9 from the power supply 8, and the difference between the fin source voltage and the potential of the capacitor 9 is sent as a signal to the external load 7. issued.

The usable light amount range of the MOS type solid-state image element is determined by the amount of charge accumulated in the capacitor 9.

Since the capacitance value of the capacitor 9 is determined by design conditions such as the area of the photodiode, the light amount range can be increased by increasing the power supply voltage. However, as shown in Figure 2, the power supply voltage of the MOS type body image sensor is
, 12, it is not possible to apply a voltage higher than a certain value to the capacitor 9 due to the influence of the threshold voltage of the switching transistor.

Let's now temporarily set the output pulse amplitudes of shift registers 2 and 3 to the third
As shown in the figure, if Vo volts is taken and the threshold voltage of the switching transistors 10 and 12 is VT, then Vo-
This means that only a voltage of VT volts can be transmitted to capacitor 9 in FIG.

In reality, the usable voltage drops further due to substrate effects and other factors. In order to solve this problem, it is possible to increase the power supply voltage 14 of shift registers 2 and 3 and increase the output pulse amplitude of the shift registers.
Periodic spike noise caused by the output pulses of the register increases, significantly degrading the image quality.

'3} Object of the invention The object of the invention is to reduce M
This provides a driving method that expands the light amount range of the OS type image sensor.

'41 General Description of the Invention As mentioned above, the gist of the present invention is to provide a method of increasing the power supply voltage applied to a photodiode of a MOS type green image element and expanding the light amount range of the MOS type image pickup element.

'5} Example Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 4 shows one embodiment of the present invention.

Normally, a MOS image sensor is divided into a photoelectric conversion section that includes a photodiode and switch circuits for horizontal and vertical scanning, and a scanning circuit section for generating scanning pulses, and each has an independent power supply section and ground section. . Therefore, as shown in Figure 4, a separate power supply 1 is connected to the ground terminal of the horizontal shift register 2.
5, and the potential at the ground end of the horizontal shift register is shifted by V, volts, while the vertical shift register 3 is connected to a power source 16 having a higher voltage than the voltage of the power source 14 applied to the horizontal shift register.

When such a power supply is connected, the output pulse of the horizontal shift register is level-shifted by V, volts, and the output pulse of the vertical shift register is level-shifted by V, as shown in Figure 5.
A pulse with larger amplitude can be obtained. As a result, a pulse with an amplitude of Vo+V, volts is applied to the gate of the horizontal scanning switching transistor shown in 12 in the second device, and a pulse with an amplitude of Vo+V, 1V is applied to the capacitor 11.
It becomes possible to apply a voltage of T.

Moreover, if the power supply 14 in FIG. 2 is varied so that the output pulse of the vertical shift register becomes approximately Vo10V, the second
It becomes possible to apply a voltage of Vo+V, 1 VT to the photodiode end of FIG. 1 as well. Increasing the power supply voltage of the vertical shift register and increasing the output pulse of the vertical shift register will also increase spike noise, but since the output pulse of the vertical shift register is generated during the horizontal blanking period of the video signal, it will not be mixed into the video signal. There is nothing to do and there is no problem.

Therefore, if the ground terminal potential of the horizontal shift register is shifted by a voltage drop corresponding to the threshold value voltage of the horizontal and vertical switching transistors, and the power supply voltage of the vertical shift register is increased, the video signal will be disturbed. It is not possible to increase the power supply voltage applied to the photodiode without increasing periodic spike noise, and M
The usable light amount range can be expanded to the OS type image sensor.

In addition, in the above explanation, the case where the power supply 14 is varied so that the output pulse of the vertical shift register becomes Wo+V was explained as an example, but the output pulse of the vertical shift register does not necessarily have to be Vo+V, and is Vo+V.
, even if it is larger. t61 Summary As described above, the method for driving a MOS group image sensor according to the present invention is highly effective because it can expand the usable light amount range of the image sensor without increasing periodic spike-like noise.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a MOS type solid-state image sensor, Fig. 2 is a diagram showing the principle of signal extraction, Fig. 3 is a diagram showing output pulses of a shift register, and Fig. 4 is a diagram showing the driving method of the present invention. FIG. 5 is a diagram showing the output pulses of the shifted register according to the horizontal shift register driving method of the present invention. Hair diagram connection Z diagram multi-diagram 5 diagram 4 multi-diagram

Claims (1)

[Claims] 1. A large number of photoelectric conversion elements arranged vertically and horizontally in a matrix, a switching transistor group for reading signals accumulated in the photoelectric conversion elements, and a shifter for opening and closing the switching transistor group in an orderly manner. In a solid-state imaging device equipped with a register, the power supply voltage applied to the vertical shift register is set higher than the power supply voltage applied to the horizontal shift register, and the potential of the substrate of the horizontal shift register, the switching transistor group, and the photoelectric conversion element are 1. A method for driving a solid-state imaging device, characterized in that the potentials applied to a group of substrates are different from each other.