VV6501 datasheet(48/60 Pages) STMICROELECTRONICS

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Optical Characteristics

VV6501

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Optical Characteristics

7.1

Optical characterisation methods

The following measurements are made based on the pixel as summarized in

Table 23.

Average sensitivity

The average sensitivity is a measure of the image sensor response to a given light stimulus. The

optical stimulus is a white light source with a color temperature of 3200K, producing uniform

illumination at the surface of the sensor package. For a color sensor, an IR blocking filter, CM500, is

added to the light source. The analog gain of the sensor is set to x1. The exposure time,

∆t, is set

as 50% of maximum. The illuminance, I, is adjusted so the average sensor output code, Xlight, is

roughly mid-range equivalent to a saturation level of 50%. Once Xlight has been recorded the

experiment is repeated with no illumination to give a value Xdark.

The sensitivity is then calculated as

. The result is expressed in volts per lux-second.

Dark signal

The dark signal is a measure of the effect of pixel leakage current on the sensor output. The

measurement is performed without illumination. As the dark signal is small the analog gain, G, of

the sensor is increased to x4. For the same reason the clock divisor is set to16. As the leakage is

highly temperature dependent, measurement is done at a controlled temperature of 25oC. The

mean sensor output is then recorded at 2 exposure settings: Xdark at the maximum exposure time;

Xblack at zero exposure.

The dark signal is calculated as

and is expressed in volts per second.

Temporal noise of pixel and readout

A measure of the temporal noise is required to quantify the noise floor. As the signal is small the

gain, G, is set to the maximum of x16. In order to remove fixed pattern noise sources it is calculated

as the standard deviation,

black, of the difference of a pair of zero exposure and zero illumination

images. Random noise is expressed in mV.

Dynamic range

The dynamic range is the measure of the maximum and minimum signal levels at which the sensor

can be used.

The figure for temporal noise is used to find the dynamic range as follows

Table 23: VV6501 Pixel overview

Parameter

Value

Unit

Size

5.6 x 5.6

µm

Architecture

3T, DDS

Saturation voltage at pixel, VSAT

(Gain x1, 1024 codes)

1.2

FD capacitance

3.0

Xlight

Xdark

–

∆tI

⋅

---------------------------------------

Xdark

Xblack

–

∆tG

⋅

-----------------------------------------

GVsat

⋅

σblack

--------------------

ÿþ

log

⋅

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