AD8021 datasheet(14/28 Pages) AD

14 / 28 page

AD5444/AD5446

Data Sheet

Rev. E | Page 14 of 28

TERMINOLOGY

Relative Accuracy or Integral Nonlinearity

Relative accuracy or integral nonlinearity is a measure of the

maximum deviation from a straight line passing through the

endpoints of the DAC transfer function. It is measured after

adjusting for zero scale and full scale and is normally expressed

in LSBs or as a percentage of full-scale reading.

Differential Nonlinearity

Differential nonlinearity is the difference between the measured

change and the ideal 1 LSB change between any two adjacent

codes. A specified differential nonlinearity of −1 LSB maximum

over the operating temperature range ensures monotonicity.

Gain Error

Gain error or full-scale error is a measure of the output error

between an ideal DAC and the actual device output. For this

DAC, ideal maximum output is VREF − 1 LSB. Gain error of the

DAC is adjustable to zero with external resistance.

Output Leakage Current

Output leakage current is current that flows in the DAC ladder

switches when the ladder is turned off. For the IOUT1 line, it can

be measured by loading all 0s to the DAC and measuring the

IOUT1 current. Minimum current flows in the IOUT2 line when

the DAC is loaded with all 1s.

Output Capacitance

Capacitance from IOUT1 or IOUT2 to AGND.

Output Current Settling Time

The amount of time it takes for the output to settle to a speci-

fied level for a full-scale input change. For this device, it is

specified with a 100 Ω resistor to ground. The settling time

specification includes the digital delay from the SYNC rising

edge to the full-scale output change.

Digital-to-Analog Glitch Impulse

The amount of charge injected from the digital inputs to the

analog output when the inputs change state. This is normally

specified as the area of the glitch in either picoamps per second

or nanovolts per second, depending upon whether the glitch is

measured as a current or voltage signal.

Digital Feedthrough

When the device is not selected, high frequency logic activ-

ity on the device’s digital inputs can be capacitively coupled

through the device to show up as noise on the IOUT1 and IOUT2

pins and, subsequently, into the following circuitry. This noise is

digital feedthrough.

Multiplying Feedthrough Error

Multiplying feedthrough error is due to capacitive feedthrough

from the DAC reference input to the DAC IOUT1 line, when all

0s are loaded to the DAC.

Total Harmonic Distortion (THD)

The DAC is driven by an ac reference. The ratio of the rms sum

of the harmonics of the DAC output to the fundamental value is

the THD. Usually only the lower-order harmonics, such as second

to fifth, are included.

THD

log

Digital Intermodulation Distortion

Second-order intermodulation (IMD) measurements are the

relative magnitudes of the fa and fb tones digitally generated by

the DAC and the second-order products at 2fa − fb and 2fb − fa.

Compliance Voltage Range

The maximum range of (output) terminal voltage for which

the device provides the specified characteristics.

Spurious-Free Dynamic Range (SFDR)

The usable dynamic range of a DAC before spurious noise

interferes or distorts the fundamental signal. SFDR is the

measure of difference in amplitude between the fundamental

and the largest harmonically or nonharmonically related spur

from dc to full Nyquist bandwidth (half the DAC sampling

rate or fS/2). Narrow-band SFDR is a measure of SFDR over

an arbitrary window size, in this case 50% of the fundamental.

Digital SFDR is a measure of the usable dynamic range of the

DAC when the signal is a digitally generated sine wave.

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