AD9925BBCZ datasheet(11/96 Pages) AD

11 / 96 page

AD9925

Rev. A | Page 11 of 96

TERMINOLOGY

Differential Nonlinearity (DNL)

An ideal ADC exhibits code transitions that are exactly 1 LSB

apart. DNL is the deviation from this ideal value. Thus, every

code must have a finite width. No missing codes guaranteed to

12-bit resolution indicates that all 4096 codes, respectively, must

be present over all operating conditions.

Peak Nonlinearity

Peak nonlinearity, a full signal chain specification, refers to the

peak deviation of the output of the AD9925 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 and is

0.5 LSB beyond the last code transition. The deviation is meas-

ured 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 appropri-

ately gained up to fill the ADC’s full-scale range.

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 con-

verted 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 AD9925, 1 LSB is 0.488 mV.

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.

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