CYII4SM1300AA CYPRESS [Cypress Semiconductor], CYII4SM1300AA Datasheet - Page 18

• Manufacturer Part Number: CYII4SM1300AA
• Description: IBIS4-1300 1.3 MPxl Rolling Shutter CMOS Image Sensor
• Manufacturer: CYPRESS [Cypress Semiconductor]

CYII4SM1300AA
Figure 14.
shows the ADC transfer characteristic. For this measurement, the ADC input was connected to a 16-bit DAC. The input
voltage was a 100 kHz triangle waveform.
The non-linear ADC conversion is intended for gamma-correction of the images. It increases contrast in dark areas and reduces
contrast in bright areas. The non-linear curve is tolerant for external pixel offset error correction. This means that pixel offset variations
can be corrected by changing the offset after the non-linear AD conversion. This is so because the non-linear transfer function is
H(s) = 1-exp(-a*s)
by design, and neglecting the offset, the relation between the non-linear output (y) and the linear output (x) is exactly:
Y = 1024 * (1 - exp(-x/713)) / (1 - exp(-1024/713))
This law yields an increased accuracy of about a factor 2 near the zero end of the scale. It is thus possible to obtain an effective 11
bit accuracy on a linear scale after post processing by applying the reverse law to the non-linear output:
Z = -2 * 713 * ln(1 - y/(1024/(1-exp(-1024/713)))) = -1426 * ln(1-y/1343.5)
Then Z is an 11-bit linear output in the range 0...2047.
Document Number: 38-05707 Rev. *C
Page 18 of 35
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