
AD9920A
Rev. B | Page 16 of 112
TERMINOLOGY
Differential Nonlinearity (DNL)
An ideal ADC exhibits code transitions that are exactly 1 LSB
apart. DNL is the deviation from this ideal value. It is often
specified in terms of resolution for which no missing codes are
guaranteed. No missing codes guaranteed to 12-bit resolution
indicates that all 4096 codes, each for its respective input, must
be present over all operating conditions.
Integral Nonlinearity (INL)
INL is defined as the maximum deviation of the actual analog
output from the ideal output, determined by a straight line
drawn from zero scale to full scale.
Peak Nonlinearity
Peak nonlinearity, a full signal chain specification, refers to the
peak deviation of the output of the AD9920A from a true straight
line. The point used as zero scale occurs 0.5 LSB before the first
code transition. Positive full scale is defined as a level 1 LSB and
0.5 LSB beyond the last code transition. The deviation is measured
from the middle of each particular output code to the true straight
line. The error is then expressed as a percentage of the 2 V ADC
full-scale signal. The input signal is always appropriately amplified
to fill the ADC full-scale range.
Power Supply Rejection (PSR)
The PSR is measured with a step change applied to the supply
pins. The PSR specification is calculated from the change in the
data outputs for a given step change in the supply voltage.
Total Output Noise
The rms output noise is measured using histogram techniques.
The standard deviation of the ADC output codes is calculated
in LSB and represents the rms noise level of the total signal
chain at the specified gain setting. The output noise can be
converted to an equivalent voltage using the relationship
1 LSB = (ADC Full Scale/2n Codes)
where n is the bit resolution of the ADC.
For the AD9920A, 1 LSB = 0.244 mV.