AD9785 datasheet(20/62 Pages) AD

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AD9785/AD9787/AD9788

Data Sheet

Rev. C | Page 20 of 62

TERMINOLOGY

Integral Nonlinearity (INL)

INL is defined as the maximum deviation of the actual analog

output from the ideal output, determined by a straight line

drawn from zero scale to full scale.

Differential Nonlinearity (DNL)

DNL is the measure of the variation in analog value, normalized

to full scale, associated with a 1 LSB change in digital input code.

Monotonicity

A DAC is monotonic if the output either increases or remains

constant as the digital input increases.

Offset Error

The deviation of the output current from the ideal of zero is

called offset error. For IOUTA, 0 mA output is expected when the

inputs are all 0s. For IOUTB, 0 mA output is expected when all

inputs are set to 1.

Gain Error

The difference between the actual and ideal output span is

called gain error. The actual span is determined by the differ-

ence between the output when all inputs are set to 1 and the

output when all inputs are set to 0.

Output Compliance Range

The output compliance range is 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.

Temperature Drift

Temperature drift is specified as the maximum change from the

ambient (25°C) value to the value at either TMIN or TMAX. For

offset and gain drift, the drift is reported in ppm of full-scale

range (FSR) per degree Celsius. For reference drift, the drift is

reported in ppm per degree Celsius.

Power Supply Rejection (PSR)

PSR is the maximum change in the full-scale output as the

supplies are varied from minimum to maximum specified

voltages.

Settling Time

Settling time is the time required for the output to reach and

remain within a specified error band around its final value,

measured from the start of the output transition.

Spurious-Free Dynamic Range (SFDR)

Spurious-free dynamic range is the difference, in decibels,

between the peak amplitude of the output signal and the peak

amplitude of the largest spurious signal in a given frequency

band from the signal. For out-of-band SFDR, the frequency

band is 0 to one half the DAC sample rate. For in-band SFDR,

the frequency band is 0 to one half the input data rate.

Total Harmonic Distortion (THD)

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

ponents to the rms value of the measured fundamental. It is

expressed as a percentage or in decibels.

Noise Spectral Density (NSD)

NSD is the noise power at the analog output measured in a 1 Hz

bandwidth.

Interpolation Filter

If the digital inputs to the DAC are sampled at a multiple rate of

fDATA (interpolation rate), a digital filter can be constructed that

has a sharp transition band near fDATA/2. Images that typically

appear around fDAC (output data rate) can be greatly suppressed.

Adjacent Channel Leakage Ratio (ACLR)

ACLR is the ratio in dBc between the measured power within a

channel relative to its adjacent channel.

Complex Image Rejection

In a traditional two-part upconversion, two images are created

around the second intermediate frequency (IF). These images

have the effect of wasting transmitter power and system band-

width. By placing the real part of a second complex modulator

in series with the first complex modulator, either the upper or

lower frequency image near the second IF can be rejected.

Sinc

Sinc is shorthand for the mathematical function

sinc(x) = sin(x)/x

This function is a useful tool for digital signal processing. The

normalized sinc function is used here and is defined as follows:

sinc(x) = sin(π × x)/(π × x)

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