EVAL-AD9838SDZ datasheet(13/32 Pages) AD

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AD9838

Rev. A | Page 13 of 32

TERMINOLOGY

Integral Nonlinearity (INL)

Total Harmonic Distortion (THD)

INL is the maximum deviation of any code from a straight line

passing through the endpoints of the transfer function. The

endpoints of the transfer function are zero scale, a point 0.5 LSB

below the first code transition (000 … 00 to 000 … 01), and full

scale, a point 0.5 LSB above the last code transition (111 … 10

to 111 … 11). The error is expressed in LSBs.

Total harmonic distortion (THD) is the ratio of the rms sum of

harmonics to the rms value of the fundamental. For the AD9838,

THD is defined as

log

THD

Differential Nonlinearity (DNL)

where:

is the rms amplitude of the fundamental.

, V3, V4, V5, and V6 are the rms amplitudes of the second

through sixth harmonics.

DNL is the difference between the measured and ideal 1 LSB

change between two adjacent codes in the DAC. A specified

DNL of ±1 LSB maximum ensures monotonicity.

Output Compliance

Signal-to-Noise Ratio (SNR)

Output compliance refers to the maximum voltage that can be

generated at the output of the DAC to meet the specifications.

When voltages greater than that specified for the output compli-

ance are generated, the AD9838 may not meet the specifications

listed in the data sheet.

SNR is the ratio of the rms value of the measured output signal

to the rms sum of all other spectral components below the

Nyquist frequency. The value for SNR is expressed in decibels.

Clock Feedthrough

There is feedthrough from the MCLK input to the analog

output. Clock feedthrough refers to the magnitude of the

MCLK signal relative to the fundamental frequency in the

output spectrum of the AD9838.

Spurious-Free Dynamic Range (SFDR)

Along with the frequency of interest, harmonics of the funda-

mental frequency and images of these frequencies are present at

the output of a DDS device. The spurious-free dynamic range

(SFDR) refers to the largest spur or harmonic present in the

band of interest. The wideband SFDR gives the magnitude of

the largest spur or harmonic relative to the magnitude of the

fundamental frequency in the 0 to Nyquist bandwidth. The

narrow-band SFDR gives the attenuation of the largest spur or

harmonic in a bandwidth of ±200 kHz about the fundamental

frequency.

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