AD9879
Rev. A | Page 10 of 32
TERMINOLOGY
Aperture Delay
The aperture delay is a measure of the sample-and-hold
amplifier (SHA) performance. It specifies the time delay
between the rising edge of the sampling clock input and when
the input signal is held for conversion.
Aperture Uncertainty (Jitter)
Aperture jitter is the variation in aperture delay for successive
samples. It is manifested as noise on the input to the ADC.
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 to a grounded channel as a full-scale signal is
applied to another channel.
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. Guaranteed
no missing codes to 10-bit resolution indicates that all 1,024
codes, respectively, must be present over all operating ranges.
Effective Number of Bits (ENOB)
For a sine wave, SINAD can be expressed in terms of the
number of bits. Using the formula
N = (SINAD − 1.76 dB∕6.02)
it is possible to determine a measure of performance expressed
as N, the effective number of bits. Thus, the effective number of
bits for a device’s sine wave inputs at a given input frequency
can be calculated directly from its measured SINAD.
Gain Error
The first code transition should occur at an analog value
1/2 LSB above full scale. The last transition should occur for an
analog value 1 1/2 LSB below the nominal full scale. Gain error
is the deviation of the actual difference between the first and
last code transitions and the ideal difference between the first
and last code transitions.
Input Referred Noise
The rms output noise is measured using histogram techniques.
The standard deviation of the ADC output code 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.
Integral Nonlinearity Error (INL)
Linearity error refers to the deviation of each individual code
from a line drawn from negative full scale through the positive
full scale. The point used as the negative full scale occurs
1/2 LSB before the first code transition. Positive full scale is
defined as a level 1 1/2 LSB beyond the last code transition. The
deviation is measured from the middle of each code to the true
straight line.
Offset Error
First transition should occur for an analog value 1/2 LSB
above −FS. Offset error is defined as the deviation of the actual
transition from that point.
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 break down, resulting in
nonlinear performance.
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.
Pipeline Delay (Latency)
Pipeline delay is the number of clock cycles between conversion
initiation and the availability of the associated output data.
Power Supply Rejection
Power supply rejection specifies the converter’s maximum full-
scale change when the supplies are varied from nominal to
minimum and maximum specified voltages.
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 all other spectral components below
the Nyquist frequency, including harmonics but excluding dc.
The value for SINAD is expressed in decibels.
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the measured input signal to
the rms sum of all other spectral components below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
Spurious-Free Dynamic Range (SFDR)
SFDR is the difference, in dB, between the rms amplitude of the
DAC output signal (or the ADC input signal) and the peak
spurious signal over the specified bandwidth (Nyquist
bandwidth, unless otherwise noted).
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, and
is expressed as a percentage or in decibels.
