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AD9831ASTZ Datasheet PDF : 16 Pages
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AD9831
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 nonfundamental
signals up to half the sampling frequency (fMCLK/2) but exclud-
ing 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 quantiza-
tion 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 con-
verter, Signal to (Noise + Distortion) = 61.96 dB.
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
AD9831, THD is defined as
THD = 20 log
(V
2
2
+V
2
3
+
V
2
4
+V
2
5
+V
2
6
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 which
can be generated at the output of the DAC to meet the specifi-
cations. When voltages greater than that specified for the
output compliance are generated, the AD9831 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 dy-
namic range (SFDR) refers to the largest spur or harmonic
which is present in the band of interest. The wide band 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
AD9831’s output spectrum.
Table I. Control Registers
Register
Size
Description
FREQ0 REG 32 Bits
FREQ1 REG 32 Bits
PHASE0 REG 12 Bits
PHASE1 REG 12 Bits
PHASE2 REG 12 Bits
PHASE3 REG 12 Bits
Frequency Register 0. This de-
fines the output frequency, when
FSELECT = 0, as a fraction of the
MCLK frequency.
Frequency Register 1. This de-
fines the output frequency, when
FSELECT = 1, as a fraction of the
MCLK frequency.
Phase Offset Register 0. When
PSEL0 = PSEL1 = 0, the contents
of this register are added to the
output of the phase accumulator.
Phase Offset Register 1. When
PSEL0 = 1 and PSEL1 = 0, the con-
tents of this register are added to
the output of the phase accumulator.
Phase Offset Register 2. When
PSEL0 = 0 and PSEL1 = 1, the con-
tents of this register are added to
the output of the phase accumulator.
Phase Offset Register 3. When
PSEL0 = PSEL1 = 1, the contents
of this register are added to the
output of the phase accumulator.
Table II. Addressing the Control Registers
A2
A1
A0
Destination Register
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
FREQ0 REG 16 LSBs
1
FREQ0 REG 16 MSBs
0
FREQ1 REG 16 LSBs
1
FREQ1 REG 16 MSBs
0
PHASE0 REG
1
PHASE1 REG
0
PHASE2 REG
1
PHASE3 REG
D15
MSB
D15 D14 D13 D12 D11
X
X
X
X MSB
Table III. Frequency Register Bits
Table IV. Phase Register Bits
–6–
D0
LSB
D0
LSB
REV. B
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