AD7367 datasheet(14/28 Pages) AD

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AD7366/AD7367

Rev. 0 | Page 14 of 28

TERMINOLOGY

Differential Nonlinearity (DNL)

DNL is the difference between the measured and the ideal

1 LSB change between any two adjacent codes in the ADC.

Integral Nonlinearity (INL)

INL is the maximum deviation from a straight line passing

through the endpoints of the ADC transfer function. The

endpoints of the transfer function are zero scale, a single (1)

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

1 LSB above the last code transition.

Zero Code Error

It is the deviation of the midscale transition (all 1s to all 0s)

from the ideal VIN voltage, that is, AGND – ½ LSB for bipolar

ranges and 2 × VREF − 1 LSB for the unipolar range.

Positive Full-Scale Error

It is the deviation of the last code transition (011…110) to

(011…111) from the ideal (that is, +4 × VREF − 1 LSB or +2 ×

VREF – 1 LSB) after the zero code error has been adjusted out.

Negative Full-Scale Error

This is the deviation of the first code transition (10…000) to

(10…001) from the ideal (that is, −4 × VREF + 1 LSB, −2 × VREF

+ 1 LSB, or AGND + 1 LSB) after the zero code error has been

adjusted out.

Zero Code Error Match

This is the difference in zero code error across all 12 channels.

Positive Full-Scale Error Match

The difference in positive full-scale error across all channels.

Negative Full-Scale Error Match

The difference in negative full-scale error across all channels.

Track-and-Hold Acquisition Time

The track-and-hold amplifier returns to track mode at the end

of a conversion. Track-and-hold acquisition time is the time

required for the output of the track-and-hold amplifier to reach

its final value, within ±½ LSB, after the end of conversion.

Signal-to-Noise (+ Distortion) Ratio (SINAD)

This ratio is the measured ratio of signal-to-noise (+ distortion)

at the output of the ADC. The signal is the rms amplitude of the

fundamental. Noise is the sum of all nonfundamental signals up

to half the sampling frequency (fS/2), excluding dc. The ratio is

dependent on the number of quantization levels in the digitiza-

tion process: the more levels, the smaller the quantization noise.

The theoretical signal-to-noise (+ distortion) ratio for an ideal

N-bit converter with a sine wave input is given by:

Signal-to-Noise (+ Distortion) = (6.02N + 1.76) dB

Thus, for a 12-bit converter, this is 74 dB.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of harmonics to the

fundamental. For the AD7366/AD7367, it is defined as:

log

)

(

THD

where:

V1 is the rms amplitude of the fundamental.

V2, V3, V4, V5, and V6 are the rms amplitudes of the second

through the sixth harmonics.

Peak Harmonic or Spurious Noise

Peak harmonic, or spurious noise, is defined as the ratio of the

rms value of the next largest component in the ADC output

spectrum (up to fS/2, excluding dc) to the rms value of the

fundamental. Normally, the value of this specification is deter-

mined by the largest harmonic in the spectrum. However, for

ADCs where the harmonics are buried in the noise floor, it is

a noise peak.

Channel-to-Channel Isolation

Channel-to-channel isolation is a measure of the level of cross-

talk between any two channels when operating in any of the

input ranges. It is measured by applying a full-scale, 150 kHz

sine wave signal to all unselected input channels and determin-

ing how much that signal is attenuated in the selected channel

with a 50 kHz signal. The figure given is the typical across all

four channels for the AD7366/AD7367 (see the Typical

Performance Characteristics section for more information).

Intermodulation Distortion

With inputs consisting of sine waves at two frequencies, fa and

fb, any active device with nonlinearities creates distortion prod-

ucts at the sum, and different frequencies of mfa ± nfb where m,

n = 0, 1, 2, 3, and so on. Intermodulation distortion terms are

those for which neither m nor n is equal to zero. For example, the

second-order terms include (fa + fb) and (fa − fb), while the

third-order terms include (2fa + fb), (2fa − fb), (fa + 2fb) and

(fa − 2fb).

The AD7366/AD7367 is tested using the CCIF standard where

two input frequencies near the top end of the input bandwidth

are used. In this case, the second-order terms are usually dis-

tanced in frequency from the original sine waves, while the

third-order terms are usually at a frequency close to the input

frequencies. As a result, the second- and third-order terms are

specified separately. The calculation of the intermodulation

distortion is as per the THD specification, where it is the ratio

of the rms sum of the individual distortion products to the rms

amplitude of the sum of the fundamentals expressed in decibels.

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