AMIS-720442-A: 400dpi Contact Image Sensor
Data Sheet
8.0 Measuring the High Frequency Performance of the Devices
The AMIS-720442-A devices were tested on an A6 length standard CIS module’s PCB. Thirteen sensors were bonded on the PCB
board along with its support circuits, such as clock buffer circuits, the shunt switch, SW and its amplifier. The board’s video line
capacitance, input capacitance of SW and input capacitance of the amplifier become part of the CAP. The A6 PCB was selected
because together with the shunt switch, SW, and with its amplifier input, the video line had a typical value of ~100pf, including its stray
from its PCB copper traces. Another reason for this selection is that the AMIS-720442-A wafer probe tests of these devices are
similarly setup using this method.
By removing RIN, the amplifier gain was set to one. Then with the total value of CAP at ~100pf the video pixels voltage amplitude gives
a measure of the approximate pixel charge. Note that the amplifier is a 1:1 buffer amplifier that serves to isolate the video line from the
measuring instruments. Further note that when the modules are produced, RIN is in the circuit as variable resistor. Then, in production
of the CIS modules, the video output amplitude, Vpavg, can be adjusted to the module’s specified level. This factory adjust is required
because the exposure is fixed (Exposure = Light Power x Time). For example, the module’s light power is fixed and integration’s time,
tint, is fixed. Note that tint is fixed in accordance to requirements of the user or is specified for the factory adjustment procedure during
production. In either case, the light exposure is fixed. Accordingly, to adjust the voltage amplitude to the specified level, RIN is used.
Since the sensor response varies as a function of color, the AMIS-720442-A is measured with a Yellow-Green LED light source, as well
as the Red (660nm) LED light source. The light sources were selected because historically, these LED light bars were used in the CIS
industry and accepted in the low-cost CIS markets. Today, the users are turning towards the light guides or light pipes as the costs
have been reduced and the technology of the image sensor continually improves. Yet, in low-cost applications and especially in mid-
size volume production, the light bars and the older image sensors persistently continues to be in demand by the scanning industry.
The high frequency performance specifications are graphical curves showing the video output, Vpavg, response to its applied light
exposure. Although four exposure response graphs serve as good design reference for the designer who has prior knowledge of the
image power that will be exposing image sensors, this is not always the case, for example, in designing and producing a CIS module.
So to this end, the A6 PCB board, used to characterize the light exposure to video response specification, is enclosed in its A6 module
housing and measured for its standard CIS parameters. These modules were fabricated exactly as their production counter-part except
that the gain of the amplifier is set one. The measurements were conducted with two different LED bars, one Yellow-Green and the
other Red.
AMI Semiconductor – May 06, M-20571-001
7
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