AD5791 datasheet(17/28 Pages) AD

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Data Sheet

AD5781

Rev. D | Page 17 of 28

TERMINOLOGY

Relative Accuracy

Relative accuracy, or integral nonlinearity (INL), is a measure of

the maximum deviation, in LSB, from a straight line passing

through the endpoints of the DAC transfer function. A typical

INL error vs. code plot is shown in Figure 5.

Differential Nonlinearity (DNL)

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

ensures monotonicity. This DAC is guaranteed monotonic. A

typical DNL error vs. code plot is shown in Figure 9.

Linearity Error Long-Term Stability

Linearity error long-term stability is a measure of the stability of

the linearity of the DAC over a long period of time. It is

specified in LSB for a time period of 500 hours and 1000 hours

at an elevated ambient temperature.

Zero-Scale Error

Zero-scale error is a measure of the output error when zero-scale

code (0x00000) is loaded to the DAC register. Ideally, the output

voltage should be VREFNS. Zero-scale error is expressed in LSBs.

Zero-Scale Error Temperature Coefficient

Zero-scale error temperature coefficient is a measure of the

change in zero-scale error with a change in temperature. It is

expressed in ppm FSR/°C.

Full-Scale Error

Full-scale error is a measure of the output error when full-scale

code (0x3FFFF) is loaded to the DAC register. Ideally, the

output voltage should be VREFPS − 1 LSB. Full-scale error is

expressed in LSBs.

Full-Scale Error Temperature Coefficient

Full-scale error temperature coefficient is a measure of the

change in full-scale error with a change in temperature. It is

expressed in ppm FSR/°C.

Gain Error

Gain error is a measure of the span error of the DAC. It is the

deviation in slope of the DAC transfer characteristic from ideal,

expressed in ppm of the full-scale range.

Gain Error Temperature Coefficient

Gain error temperature coefficient is a measure of the change in

gain error with a change in temperature. It is expressed in ppm

FSR/°C.

Midscale Error

Midscale error is a measure of the output error when midscale

code (0x20000) is loaded to the DAC register. Ideally, the output

voltage should be (VREFPS – VREFNS)/2 +VREFNS. Midscale error is

expressed in LSBs.

Midscale Error Temperature Coefficient

Midscale error temperature coefficient is a measure of the

change in mid-scale error with a change in temperature. It is

expressed in ppm FSR/°C.

Output Slew Rate

Slew rate is a measure of the limitation in the rate of change of

the output voltage. The slew rate of the AD5781 output voltage

is determined by the capacitive load presented to the VOUT pin.

The capacitive load in conjunction with the 3.4 kΩ output

impedance of the AD5781 set the slew rate. Slew rate is

measured from 10% to 90% of the output voltage change and is

expressed in V/µs.

Output Voltage Settling Time

Output voltage settling time is the amount of time it takes for

the output voltage to settle to a specified level for a specified

change in voltage. For fast settling applications, a high speed

buffer amplifier is required to buffer the load from the 3.4 kΩ

output impedance of the AD5781, in which case, it is the

amplifier that determines the settling time.

Digital-to-Analog Glitch Impulse

Digital-to-analog glitch impulse is the impulse injected into the

analog output when the input code in the DAC register changes

state. It is specified as the area of the glitch in nV-sec and is

measured when the digital input code is changed by 1 LSB at

the major carry transition (see Figure 42).

Output Enabled Glitch Impulse

Output enabled glitch impulse is the impulse injected into the

analog output when the clamp to ground on the DAC output is

removed. It is specified as the area of the glitch in nV-sec (see

Figure 48).

Digital Feedthrough

Digital feedthrough is a measure of the impulse injected into

the analog output of the DAC from the digital inputs of the

DAC but is measured when the DAC output is not updated. It is

specified in nV-sec and measured with a full-scale code change

on the data bus, that is, from all 0s to all 1s, and vice versa.

Spurious Free Dynamic Range (SFDR)

Spurious free dynamic range is the usable dynamic range of a

DAC before spurious noise interferes or distorts the fundamental

signal. It is measured 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). SFDR is measured when the signal is a

digitally generated sine wave.

Total Harmonic Distortion (THD)

Total harmonic distortion is the ratio of the rms sum of the

harmonics of the DAC output to the fundamental value. Only

the second to fifth harmonics are included.

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