AD9878 datasheet(13/36 Pages) AD

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AD9878

Rev. A | Page 13 of 36

TERMINOLOGY

Differential Nonlinearity Error (DNL, No Missing Codes)

An ideal converter exhibits code transitions that are exactly 1 LSB

apart. DNL is the deviation from this ideal value. No missing

codes indicates that all of the ADC codes must be present over

all operating ranges.

Integral Nonlinearity Error (INL)

Linearity error refers to the deviation of each individual code from

a line drawn from negative full scale through positive full scale.

The point used as negative full scale occurs ½ LSB before the first

code transition. Positive full scale is defined as a level 1½ LSB

beyond the last code transition. The deviation is measured from

the middle of each code to the true straight line.

Phase Noise

Single-sideband, phase-noise power is specified relative to the

carrier (dBc/Hz) at a given frequency offset (1 kHz) from the

carrier. Phase noise can be measured directly in single-tone

transmit mode with a spectrum analyzer that supports noise

marker measurements. It detects the relative power between

the carrier and the offset (1 kHz) sideband noise and takes

the resolution bandwidth (RBW) into account by subtracting

10 × log(RBW). It also adds a correction factor that compensates

for the implementation of the resolution bandwidth, log display,

and detector characteristic.

Output Compliance Range

The range of allowable voltage at the output of a current-output

DAC. Operation beyond the maximum compliance limits can

cause either output stage saturation or breakdown, resulting in

nonlinear performance.

Spurious-Free Dynamic Range (SFDR)

The difference, in dB, between the rms amplitude of the DAC

output signal (or ADC input signal) and the peak spurious signal

over the specified bandwidth (Nyquist bandwidth, unless

otherwise noted).

Pipeline Delay (Latency)

The number of clock cycles between conversion initiation and

the associated output data being made available.

Offset Error

The first code transition should occur at an analog value ½ LSB

above negative full scale. Offset error is defined as the deviation

of the actual transition from that point.

Gain Error

The first code transition should occur at an analog value ½ LSB

above negative full scale. The last transition should occur for an

analog value 1½ LSB below the nominal full scale. Gain error

is the deviation of the actual difference between first and last

code transitions and the ideal difference between first and last

code transitions.

Aperture Delay

The aperture delay is a measure of the sample-and-hold amplifier

(SHA) performance that specifies the time delay between the

rising edge of the sampling clock input and when the input

signal is held for conversion.

Aperture Jitter

Aperture jitter is the variation in aperture delay for successive

samples and is manifested as noise on the input to the ADC.

Input Referred Noise

The rms output noise is measured using histogram techniques.

The standard deviation of the ADC output codes is calculated

in LSB, and converted to an equivalent voltage. This results in a

noise figure that can be directly referred to the input of the MxFE.

Signal-to-Noise and Distortion (SINAD) Ratio

SINAD is the ratio of the rms value of the measured input signal

to the rms sum of other spectral components below the Nyquist

frequency, including harmonics, but excluding dc. The value for

SINAD is expressed in decibels.

Effective Number of Bits (ENOB)

For a sine wave, SINAD can be expressed in terms of the number

of bits. Using the following formula, it is possible to get a measure

of performance expressed as N, the effective number of bits:

(

)

−

= SINAD

Thus, the effective number of bits for a device for sine wave

inputs at a given input frequency can be calculated directly

from its measured SINAD.

Signal-to-Noise Ratio (SNR)

SNR is the ratio of the rms value of the measured input signal

to the rms sum of other spectral components below the Nyquist

frequency, excluding harmonics and dc. The value for SNR is

expressed in decibels.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of the first six harmonic

components to the rms value of the measured input signal.

It is expressed as a percentage, or in decibels.

Power Supply Rejection

Power supply rejection specifies the converter’s maximum full-

scale change when the supplies are varied from nominal to

minimum or maximum specified voltages.

Channel-to-Channel Isolation (Crosstalk)

In an ideal multichannel system, the signal in one channel does

not influence the signal level of another channel. The channel-

to-channel isolation specification is a measure of the change

that occurs in a grounded channel as a full-scale signal is

applied to another channel.

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