AD9835_15 Datasheet, PDF (12/28 Pages) Analog Devices – 50 MHz Direct Digital Synthesizer

AD9835
TERMINOLOGY
Integral Nonlinearity
This 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.
Differential Nonlinearity
This is the difference between the measured and ideal 1 LSB
change between two adjacent codes in the DAC.
Signal to (Noise + Distortion)
Signal to (Noise + Distortion) is measured signal to noise at
the output of the DAC. The signal is the rms magnitude of the
fundamental. Noise is the rms sum of all the non-fundamental
signals up to half the sampling frequency (fMCLK/2) but excluding
the dc component. Signal to (Noise + Distortion) is dependent
on the number of quantization levels used in the digitization
process; the more levels, the smaller the quantization noise. The
theoretical Signal to (Noise + Distortion) ratio for a sine wave
input is given by
Signal to (Noise + Distortion) = (6.02N + 1.76) dB
where N is the number of bits. Thus, for an ideal 10-bit converter,
Signal to (Noise + Distortion) = 61.96 dB.
Data Sheet
Total Harmonic Distortion
Total Harmonic Distortion (THD) is the ratio of the rms sum of
harmonics to the rms value of the fundamental. For the AD9835,
THD is defined as
( ) THD = 20 log V22 + V32 + V4 2 + V52 + V62
V₁
where V1 is the rms amplitude of the fundamental and V2, V3,
V4, V5, and V6 are the rms amplitudes of the second through the
sixth harmonic.
Output Compliance
The output compliance refers to the maximum voltage that
can be generated at the output of the DAC to meet the specifica-
tions. When voltages greater than that specified for the output
compliance are generated, the AD9835 may not meet the
specifications listed in the data sheet.
Spurious Free Dynamic Range
Along with the frequency of interest, harmonics of the funda-
mental frequency and images of the MCLK frequency 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 harmonic or spur relative to the magnitude of the
fundamental frequency in the bandwidth ±2 MHz about the
fundamental frequency. The narrow band SFDR gives the
attenuation of the largest spur or harmonic in a bandwidth
of ±50 kHz about the fundamental frequency.
Clock Feedthrough
There will be 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 AD9835’s
output spectrum.
Rev. A | Page 12 of 28