ADC and DAC linearity in Readout Card

ADC Linearity

RevB uses AD6644 and RevE uses AD9252

In general, ADC non-linearity can be broken down to offset-error, gain-error, DNL error and INL error.

DNL or Differential Non-linearity error

DNL is the difference between an actual analog-step-width and the ideal value corresponding to 1 lsb. For an ideal ADC, DNL is zero and all transition values are spaced exactly 1 lsb apart. Listed in the datasheet, DNL for AD9252 is ±0.4LSB (typical) and for AD6644 is ±0.25LSB (typical). AD9252 datasheet includes a DNL plot for f_in=2.3MHz.

Test Results

A 200kHz 0mV-offset 250mV-pk-pk triangular wave is applied to the input of the preamp chain (JP1) through a 26dB attenuator.

On a Rev D card, We ran rc_dnl_test script and the calculated DNLs are:

>rc_dnl_test -a SRC-213
ch0: 0.177 LSB SRC-213_1262987653 (with no R37, input at R19)
ch2: 0.432 LSB(50-Ohm termination card plugged in)
ch3: 0.421 LSB (50-Ohm termination card plugged in)
ch4: 0.147 LSB SRC-213_1262987653
ch5: 0.181 LSB SRC-213_1262987653
ch6: 0.149 LSB SRC-213_1262987653
ch7: 0.149 LSB SRC-213_1262987653

The ramp is slightly clipped on both sides, check 1262991813_raw

INL or Integral non-linearity error

This is typical of less importance in imaging systems. INL is the deviation of the ADC code transfer function from the straight line. Listed in the datasheet, INL for ADC9252 is 1.5bits

DAC Linearity

Readout Card uses AD9744. According to the datasheet the DNL is ±0.5 lsb.