KR20060077529A - Method of driving a cmos image sensor - Google Patents

Abstract

The present invention proposes a method of driving a CMOS image sensor. The pixel of the CMOS image sensor is composed of a reset transistor, a transfer transistor, a driving transistor, a selection transistor, and a photodiode. Here, the gate voltage of the reset transistor and the transfer transistor is externally applied, but the supply of the externally applied voltage is provided by a bootstrapping method so that the gate voltage of the reset transistor and the transfer transistor can be applied higher than the normal gate applied voltage.

CMOS image sensor, pixel, transistor, photodiode

Description

Method of Driving a CMOS Image Sensor

1 is a diagram showing an equivalent circuit and timing diagram of one pixel of a CMOS image sensor according to the prior art.

2 is a diagram showing an equivalent circuit of a pixel of the CMOS image sensor according to the present invention, and thus a timing diagram.

3 is a diagram comparing the readout waveform of a pixel in accordance with the present invention and the prior art;

Explanation of symbols for the main parts of the drawings

11: Reset Transistor 12: Transfer Transistor

13 drive transistor 14 selection transistor

15 photodiode

The present invention relates to a method of driving a CMOS image sensor.

1 is a diagram showing an equivalent circuit and timing diagram of one pixel of a CMOS image sensor according to the prior art.

As shown in FIG. 1, one pixel of a conventional CMOS image sensor has a read-out circuit composed of four transistors.

In FIG. 1, one pixel of the conventional CMOS image sensor includes four transistors, that is, a reset transistor 1 and a transfer transistor 2. , A drive transistor 3, and a selection transistor 4 and one photodiode 5.

As described above, the gate voltages of the four transistors 1-4 are applied externally or internally.

However, when the gate voltages of the reset transistor 1 and the transfer transistor 2 are externally applied, according to the circuit structure of FIG. 1, the reset transistor 1 ) And the voltage drop generated by the threshold voltage of the transfer transistor 2 lowers the voltage range at the floating diffusion FD shown in FIG. Compared to the external or internal supply voltage provided, the voltage VDL that appears through the floating diffusion (FD) and its source follower is farther apart, so that the dynamic range of the signal read out range).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the CMOS image sensor (CMOS) can widen the dynamic range of the CMOS image sensor by increasing the operating range of the signal without raising the power supply voltage of the CMOS image sensor. The purpose is to provide a method of driving an image sensor).

According to one embodiment of the present invention for achieving the above object, a method of driving a CMOS image sensor includes a pixel of a CMOS image sensor composed of a reset transistor, a transfer transistor, a driving transistor, a selection transistor, and a photodiode. In this case, the gate voltages of the reset transistors and the transfer transistors are applied externally, and the supply of the externally applied voltages is provided by the bootstrapping method so that the gate voltages of the reset transistors and the transfer transistors are higher than the normal gate applied voltages.

Preferably, the gate voltages of the reset transistor and the transfer transistor are applied by using a bootstrapping circuit in a vertical scanning circuit, thereby actually The gate voltage of the reset transistor and the transfer transistor is increased without increasing the power supply voltage.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 2 is a diagram showing an equivalent circuit of a pixel of the CMOS image sensor according to the present invention and thus a timing diagram. 3 is a diagram comparing the readout waveform of a pixel according to the present invention and prior art.

As shown in Fig. 2, the CMOS image sensor according to the present invention reads out a signal from each pixel (or pixel) that converts a signal from an optical signal to an electrical signal, as in the above-described conventional pixel. Driving circuits are formed in the periphery of the pixel to read out, each pixel consisting of one photodiode and four transistors.

An object of the present invention is to provide a method for extending a dynamic range of a signal without raising a power supply voltage of a CMOS image sensor. Therefore, it is intended to increase the dynamic range of the CMOS image sensor. That is, the CMOS image sensor includes a reset transistor 11, a transfer transistor 12, a drive transistor 13, a selection transistor 14, and one photodiode. (15).

That is, in the CMOS image sensor using four read-out transistors as shown in FIG. 2, the reset transistor 11 and the transfer transistor are used. By using a bootstrapping circuit in a vertical scanning circuit (not shown) by applying a gate voltage applied to the circuit 12), the reset transistor without increasing the power supply voltage externally. The gate voltages of the reset transistor 11 and the transfer transistor 12 are raised.

Accordingly, a voltage drop caused by a threshold voltage loss of the reset transistor 11 or the transfer transistor 12 is prevented to prevent the floating diffusion region FD. Increasing the voltage at) increases the swing of the signal voltage.

Therefore, the dynamic range of the CMOS image sensor is increased or the image lag due to the residual charge remaining in the region of the photodiode 15 is minimized.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

As described above, according to the present invention, the operating voltage of the floating diffusion shown in Fig. 2 can be raised, and as shown in Fig. 3, the voltage swing width on the data line in the low voltage direction is increased. It can be widened. Therefore, the power supply voltage can be lowered by that much, and the additional signal can be used as wider.

Claims (2)

In a pixel of a CMOS image sensor composed of a reset transistor, a transfer transistor, a driving transistor, a selection transistor, and a photodiode, A method of driving a CMOS image sensor which applies a gate voltage of a reset transistor and a transfer transistor from an external source, and provides a supply of the external applied voltage by a boot strapping method so that a higher than a normal gate application voltage can be applied.  The method of claim 1, wherein the gate voltage of the reset transistor and the transfer transistor is applied by using a bootstrapping circuit in a vertical scanning circuit. The method of driving a CMOS image sensor, characterized in that to increase the gate voltage of the reset transistor and the transfer transistor without actually increasing the power supply voltage from the outside.

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