JPS6141973A - Method of evaluating light response characteristic of image sensor - Google Patents

Abstract

PURPOSE:To evaluate light response characteristics of an image sensor simply by measuring the electrode capacity, light resistance and dark resistance of single or plural picture elements of the image sensor. CONSTITUTION:In an image sensor having structure in which a picture element holds a photoconductor between two electrodes, light response waveform of the image sensor is obtained from a specified equation if the dark resistance, light resistance and capacity between electrodes of the picture element and power source voltage and load resistance are known. Measurement of the dark resistance, light resistance and capacity between electrodes of the image sensor and power source voltage and load resistance is easy, and accordingly, evaluation light response characteristics of an image sensor can be made simply by using the specified equation. This method of evaluation becomes more effective in the case of many picture elements.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for evaluating optical response characteristics of an image sensor.

<Prior art> An image sensor in which one pixel has a structure in which a photoconductor is sandwiched between two electrodes has a structure in which a photoconductor is sandwiched between two electrodes, and one electrode is a transparent electrode. There are two known types: one in which two comb-shaped parallel electrodes are provided on a photoconductor, and one in which two comb-shaped parallel electrodes are provided on a photoconductor.

In the conventional method for evaluating the photoresponse characteristics of image sensors, the amount of light irradiated to the image sensor is changed stepwise, and the resistance change that occurs in the image sensor at this time is converted into a current change, and this is converted through an appropriate load resistance. Read as the individual response of the voltage generated between both terminals of the load resistor. At this time, a commonly used method is to evaluate the photoresponse characteristics by reading the response signal with a synchroscope or the like.

However, this method requires a great deal of effort and time to evaluate the photoresponse characteristics of each pixel in an image sensor with a large number of pixels.

<Objective of the Invention> The present invention has been made in view of the above circumstances, and its object is to provide a simplified method for evaluating optical response characteristics of an image sensor.

<Structure of the Invention> In the present invention, in an image sensor having a structure in which one pixel has a photoconductor sandwiched between two electrodes, the capacitance between the electrodes of a single or plural pixels of this image sensor and the The present invention is characterized in that the photoresponse characteristics of a single pixel or a plurality of pixels of the image sensor are evaluated by measuring resistance and dark resistance.

<Example> An embodiment of the present invention will be described below.

Figure 1 shows an equivalent circuit of a circuit for evaluating the photoresponse characteristics of an image sensor in which one pixel has a structure in which a photoconductor is sandwiched between two electrodes. In the figure, E is the power supply and R is the image sensor. C is the electrical resistance of a single pixel or multiple pixels of the image sensor, C is the inter-electrode capacitance of the single pixel or multiple pixels of the image sensor, and RL is the load resistance.

Now, as shown in Fig. 2, if the electrical resistance of the pixel when the image sensor is not irradiated with light is R1, then when the image sensor is irradiated with light and the amount of light changes stepwise, the As shown in Figure 3, the electrical resistance of the pixel is R
At this time, the electrical resistance R1 of the pixel when no light is irradiated is called the dark resistance, and the electrical resistance R2 of the pixel when the pixel is irradiated with light is called the bright resistance.

Hereinafter, a transient phenomenon when transitioning from a first steady state in which no light is irradiated to a second steady state in which light is irradiated will be considered.

The dark resistance of the pixel of the image sensor is R+, the bright resistance is R2,
The inter-electrode capacitance is C1, the current flowing through the resistor R2 is AI, the charge of the inter-electrode capacitance is q, the current flowing through the inter-electrode capacitance is C, and the current flowing through the load resistor R is added to the load resistor RL. When the output voltage is EO and the power supply voltage is E, the following equation holds true.

RL=+R27＾ 凋E −・■ ÷−R2□B ・−・−■ 1st +j (mt '−■ Deriving the relational expression for AC only, from formulas ■ and ■, t R−q /CR2r t −q /C
R2+=c.

Substitute into the formula ■, CR2R sidt Integrating both sides with the constant term A, we get Further, by converting the constant term A, the above equation becomes as follows.

CR2E CRt E (R1+ RL) (R2+ RL) Since R2B q t i-4c+AR, (R1+ RL) (R2+ RL)
CI? 2 H, and the output voltage EO becomes E
Since O-R is □, it becomes.

That is, the output voltage EO can be determined by providing the dark resistance R1, bright resistance R2, and interelectrode capacitance C of the pixel, as well as the power supply voltage E and the load resistance RL.

In order to examine the suitability of the above equation (2), the following simulation was performed.

As shown in Figure 4, the output voltage EO when the switch SW is closed to the contact 1 side to enter the first steady state, and then the switch SW is closed to the contact 2 side to switch to the second steady state. The waveform was observed and compared with the theoretical value obtained from equation (2). Fifth
The figure shows the theoretical value of the output voltage EO when the power supply voltage is E-5V, the dark resistance R1-100 is Ω, the bright resistance R2 is Ω, the interelectrode capacitance C-630μF, and the load resistance RL is 10Ω. The results of actual measurements are shown. In the figure, the solid line a indicates the measured value, and the broken line indicates the theoretical value.

As is clear from the results of this simulation, the theoretical value and the measured value almost match, and Equation (2) expresses the optical response characteristic of the image sensor. Therefore, if the power supply voltage and load resistance are known as well as the dark resistance, bright resistance, and interelectrode capacitance of the pixel, the photoresponse waveform of the image sensor can be obtained from equation (2). Since it is easy to measure the dark resistance, bright resistance, interelectrode capacitance, power supply voltage, and load resistance of the image sensor, the photoresponse characteristics of the image sensor can be easily evaluated using this equation (2). This method of evaluating photoresponse characteristics of an image sensor becomes advantageous when the number of pixels is large.

<Effects of the Invention> As explained above, in the present invention, the interelectrode capacitance, bright resistance, and dark resistance of a single or multiple pixels of an image sensor are measured to obtain the photoresponse characteristics of the pixel. , it is possible to easily evaluate the photoresponse characteristics of an image sensor.

[Brief explanation of the drawing]

1 to 3 are circuit diagrams showing equivalent circuits of the embodiments of the present invention, FIG. 4 is a circuit diagram showing a simulation circuit, and FIG. 5 is a graph showing theoretical values and actually measured values of the output voltage Eo. C・-electrode capacitance

Claims (1)

[Claims] (1) In an image sensor having a structure in which one pixel has a photoconductor sandwiched between two electrodes, measure the interelectrode capacitance, bright resistance, and dark resistance of a single or multiple pixels of this image sensor. A method for evaluating photoresponse characteristics of an image sensor, characterized in that the photoresponse characteristics of a single or a plurality of pixels of the image sensor are evaluated.