Data Sheet

ADuCM330/ADuCM331

Rev. C | Page 13 of 16

TERMINOLOGY

Conversion Rate

The conversion rate specifies the rate at which an output result

is available from the ADC, after the ADC has settled.

The Σ-Δ conversion techniques used on this device means that

although the ADC front-end signal is oversampled at a relatively

high sample rate, a subsequent digital filter is used to decimate

the output, giving a valid 20-bit data conversion result at output

rates from 1 Hz to 8 kHz.

Note that, when software switches from one input to another

(on the same ADC), the digital filter must first be cleared and

then allowed to average a new result. Depending on the con-

figuration of the ADC and the type of filter, this averaging can

require multiple conversion cycles.

Integral Nonlinearity (INL)

INL 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, a point ½ LSB

below the first code transition, and full scale, a point ½ LSB

above the last code transition (111…110 to 111…111). The

error is expressed as a percentage of full scale.

Positive INL is defined as the deviation from a straight line

through ½ LSB above midscale code transition to ½ LSB above

the last code transition.

Negative INL is defined as the deviation from a straight line

from a point ½ LSB below the first code transition to a point

½ LSB above the midscale code transition.

No Missing Codes

No missing codes is a measure of the differential nonlinearity of

the ADC. The error is expressed in bits and specifies the number

guaranteed to occur through the full ADC input range.

Offset Error

Offset error is the deviation of the first code transition ADC

input voltage from the ideal first code transition.

Offset Error Drift

Offset error drift is the variation in absolute offset error with

respect to temperature. This error is expressed as LSB/°C or nV/°C.

Gain Error

Gain error is a measure of the span error of the ADC. It is a

measure of the difference between the measured and the ideal

span between any two points in the transfer function.

Output Noise

The output noise is specified as the standard deviation (or 1 × Σ)

of ADC output codes distribution collected when the ADC

input voltage is at a dc voltage. It is expressed as μV rms or

nV rms. The output, or rms noise, is used to calculate the

effective resolution of the ADC as defined by the following

equation:

The peak-to-peak noise is defined as the deviation of codes that fall

within 6.6 × Σ of the distribution of ADC output codes collected

when the ADC input voltage is at dc. The peak-to-peak noise is

therefore calculated as 6.6 × the rms noise.

The peak-to-peak noise can be used to calculate the ADC (noise

free, code) resolution for which there is no code flicker within a

6.6 × Σ limit as defined by the following equation:

to-Peak Noise) bits