AD9974BBCZ datasheet(13/52 Pages) AD

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AD9974

Rev. A | Page 13 of 52

TERMINOLOGY

Differential Nonlinearity (DNL)

An ideal ADC exhibits code transitions that are exactly 1 LSB

apart. DNL is the deviation from this ideal value. Therefore,

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

to 14-bit resolution indicates that all 16,384 codes, each for its

respective input, 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 AD9974 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 gained up to fill the ADC 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

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 AD9974,

1 LSB is approximately 122.0 μV.

Linearity Mismatch

The linearity mismatch is calculated by taking the difference in

INL of the two channels at Input X, and then expressing the

difference as a percentage of the output code at X. The values

given in Table 2 are obtained over the range of 1⁄16 and

maximum of the output code. The general trend is for the

linearity mismatch to decrease as the output approaches the

maximum code, as shown in Figure 8.

)

(

)

(

)

(

(%)

Code

Output

INL

Mismatch

Linearity

−

CHANNEL B

INPUT VOLTAGE

XFS

INL A(X)

INL B(X)

OUTPUT (X)

MAX/16

MAX

CHANNEL A

IDEAL

Figure 13. Linearity Mismatch Definition

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.

Crosstalk

The crosstalk is measured while applying a full-scale step to

one channel and measuring the interference on the opposite

channel.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

384

)

(

log

)

(

LSB

Interferen

Crosstalk

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