AD5433 datasheet(16/32 Pages) AD

16 / 32 page

AD5424/AD5433/AD5445

Rev. B | Page 16 of 32

TERMINOLOGY

Relative Accuracy

Relative accuracy or endpoint 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 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 these

DACs, ideal maximum output is VREF – 1 LSB. Gain error of the

DACs is adjustable to 0 with external resistance.

Output Leakage Current

Output leakage current is current that flows in the DAC ladder

switches when these are turned off. For the IOUT1 terminal, 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

This is the amount of time it takes for the output to settle to a

specified level for a full-scale input change. For these devices, it

is specified with a 100 Ω resistor to ground.

The settling time specification includes the digital delay from

the CS rising edge to the full-scale output change.

Digital to Analog Glitch lmpulse

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 pA seconds or nV

seconds, depending upon whether the glitch is measured as a

current or voltage signal.

Digital Feedthrough

When the device is not selected, high frequency logic activity

on the device digital inputs may be capacitively coupled

through the device to show up as noise on the IOUT pins and

subsequently in the following circuitry. This noise is called

digital feedthrough.

Multiplying Feedthrough Error

This is the error due to capacitive feedthrough from the DAC

reference input to the DAC IOUT1 terminal 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 are included,

such as second to fifth.

(

)

log

THD

Digital Intermodulation Distortion

Second-order intermodulation distortion (IMD) measurements

are the relative magnitude of the fa and fb tones generated

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

and 2fb − fa.

Spurious-Free Dynamic Range (SFDR)

SFDR is the usable dynamic range of a DAC before spurious

noise interferes or distorts the fundamental signal. It is mea-

sured by the 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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