AD7715_15 datasheet(11/40 Pages) AD

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AD7715

Rev. D | Page 11 of 40

TERMINOLOGY

Integral Nonlinearity

This is the maximum deviation of any code from a straight

line passing through the endpoints of the transfer function.

The endpoints of the transfer function are zero-scale (not to

be confused with bipolar zero), a point 0.5 LSB below the first

code transition (000 … 000 to 000 … 001) and Full-Scale, a

point 0.5 LSB above the last code transition (111 … 110 to 111

… 111). The error is expressed as a percentage of full scale.

Positive Full-Scale Error

Positive Full-Scale Error is the deviation of the last code

transition (111 . . . 110 to 111 . . . 111) from the ideal AIN(+)

voltage (AIN(−) + VREF/GAIN −3/2 LSBs). It applies to both

unipolar and bipolar analog input ranges.

Unipolar Offset Error

Unipolar Offset Error is the deviation of the first code transition

from the ideal AIN(+) voltage (AIN(−) + 0.5 LSB) when operating

in the unipolar mode.

Bipolar Zero Error

This is the deviation of the midscale transition (0111 . . . 111 to

1000 . . . 000) from the ideal AIN(+) voltage (AIN(−) − 0.5 LSB)

when operating in the bipolar mode.

Gain Error

This is a measure of the span error of the ADC. It includes full-

scale errors but not zero-scale errors. For unipolar input ranges

it is defined as (full scale error—unipolar offset error) while for

bipolar input ranges it is defined as (full-scale error—bipolar

zero error).

Bipolar Negative Full-Scale Error

This is the deviation of the first code transition from the ideal

AIN(+) voltage (AIN(−) − VREF/GAIN + 0.5 LSB), when

operating in the bipolar mode.

Positive Full-Scale Overrange

Positive full-scale overrange is the amount of overhead available

to handle input voltages on AIN(+) input greater than AIN−) +

VREF/GAIN (for example, noise peaks or excess voltages due

to system gain errors in system calibration routines) without

introducing errors due to overloading the analog modulator

or overflowing the digital filter.

Negative Full-Scale Overrange

This is the amount of overhead available to handle voltages

on AIN(+) below AIN(−) −VREF/GAIN without overloading the

analog modulator or overflowing the digital filter. Note that the

analog input accepts negative voltage peaks even in the unipolar

mode provided that AIN(+) is greater than AIN(−) and greater

than AGND − 30 mV.

Offset Calibration Range

In the system calibration modes, the AD7715 calibrates its

offset with respect to the analog input. The offset calibration

range specification defines the range of voltages that the AD7715

can accept and still calibrate offset accurately.

Full-Scale Calibration Range

This is the range of voltages that the AD7715 can accept in the

system calibration mode and still calibrate full scale correctly.

Input Span

In system calibration schemes, two voltages applied in sequence

to the AD7715’s analog input define the analog input range. The

input span specification defines the minimum and maximum

input voltages from zero to full scale that the AD7715 can accept

and still calibrate gain accurately.

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