AD9775-EBZ Analog Devices Inc, AD9775-EBZ Datasheet - Page 39

• Manufacturer Part Number: AD9775-EBZ
• Description: 14Bit 160 MSPS Dual TxDAC+ D/A Converter
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9775-EBZ

• Number Of Dac's: 2
• Number Of Bits: 14
• Outputs And Type: 2, Differential
• Sampling Rate (per Second): 160M
• Data Interface: Parallel
• Settling Time: 11ns
• Dac Type: Current
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9775
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The complex carrier synthesized in the AD9775 digital
modulator is accomplished by creating two real digital carriers
in quadrature. Carriers in quadrature cannot be created with
the modulator running at f
tion only functions with modulation rates of f
Regions A and B of Figure 83 to Figure 88 are the result of the
complex signal described previously, when complex modulated
in the AD9775 by +e
complex signal described previously, again with positive
frequency components only, modulated in the AD9775 by –e
The analog quadrature modulator after the AD9775 inherently
modulates by +e
Region A
Region A is a direct result of the upconversion of the complex
signal near baseband. If viewed as a complex signal, only the
images in Region A remain. The complex Signal A, consisting
of positive frequency components only in the digital domain,
has images in the positive odd Nyquist zones (1, 3, 5, …), as
well as images in the negative even Nyquist zones. The
appearance and rejection of images in every other Nyquist zone
becomes more apparent at the output of the quadrature
modulator. The A images appear on the real and the imaginary
outputs of the AD9775, as well as on the output of the quadrature
modulator, where the center of the spectral plot now represents
the quadrature modulator LO, and the horizontal scale now
represents the frequency offset from this LO.
Region B
Region B is the image (complex conjugate) of Region A. If a
spectrum analyzer is used to view the real or imaginary DAC
outputs of the AD9775, Region B appears in the spectrum.
However, on the output of the quadrature modulator, Region B
is rejected.
Region C
Region C is most accurately described as a downconversion, as
the modulating carrier is –e
the images in Region C remain. This image appears on the real
and imaginary outputs of the AD9775, as well as on the output of
the quadrature modulator, where the center of the spectral plot
now represents the quadrature modulator LO and the horizontal
scale represents the frequency offset from this LO.
Region D
Region D is the image (complex conjugate) of Region C. If a
spectrum analyzer is used to view the real or imaginary DAC
outputs of the AD9775, Region D appears in the spectrum.
However, on the output of the quadrature modulator, Region D
is rejected.
Figure 89 to Figure 96 show the measured response of the AD9775
and AD8345 given the complex input signal to the AD9775 in
Figure 89. The data in these graphs was taken with a data rate of
12.5 MSPS at the AD9775 inputs. The interpolation rate of 4× or 8×
gives a DAC output data rate of 50 MSPS or 100 MSPS. As a result,
jωt
.
jωt
. Regions C and D are the result of the
DAC
jωt
. If viewed as a complex signal, only
/2. As a result, complex modula-
DAC
/4 and f
DAC
/8.
Rev. E | Page 39 of 56
jωt
.
the high end of the DAC output spectrum in these graphs is the
first null point for the sin(x)/x roll-off, and the asymmetry of the
DAC output images is representative of the sin(x)/x roll-off over the
spectrum. The internal PLL was enabled for these results. In
addition, a 35 MHz third-order low-pass filter was used at the
AD9775/AD8345 interface to suppress DAC images.
An important point can be made by looking at Figure 91 and
Figure 93. Figure 91 represents a group of positive frequencies
modulated by complex +fDAC/4, while Figure 93 represents a
group of negative frequencies modulated by complex −fDAC/4.
When looking at the real or imaginary outputs of the AD9775,
as shown in Figure 91 and Figure 93, the results look identical.
However, the spectrum analyzer cannot show the phase
relationship of these signals. The difference in phase between
the two signals becomes apparent when they are applied to the
AD8345 quadrature modulator, with the results shown in
Figure 92 and Figure 94.
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
0
0
–2.0
–4.0
Figure 84. 4× Interpolation, Complex fDAC/4 Modulation
D
Figure 83. 2× Interpolation, Complex f
D
–1.5
–3.0
A
A
–1.0
–2.0
B
B
–0.5
–1.0
f
f
OUT
OUT
C
C
(LO)
(LO)
(×
(×
0
0
f
f
DATA
DATA
D
D
)
)
0.5
1.0
A
A
DAC
1.0
2.0
/4 Modulation
B
B
1.5
3.0
C
C
AD9775
2.0
4.0