AD9777-EBZ Analog Devices Inc, AD9777-EBZ Datasheet - Page 42

• Manufacturer Part Number: AD9777-EBZ
• Description: 16Bit 400 MSPS Dual TxDAC+ D/A Converter
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9777-EBZ

• Number Of Dac's: 2
• Number Of Bits: 16
• 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: AD9777
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9777
The complex carrier synthesized in the AD9777 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
Region A and Region B of Figure 83 to Figure 88 are the result
of the complex signal described previously, when complex
modulated in the AD9777 by +e
the result of the complex signal described previously, again with
positive frequency components only, modulated in the AD9777
by −e
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 remains. 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, and so
on), 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 AD9777, 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 AD9777, Region B appears in the spectrum.
However, on the output of the quadrature modulator, Region B
is rejected.
jωt
. The analog quadrature modulator after the AD9777
DAC
jωt
.
/2. As a result, complex modula-
jωt
. Region C and Region D are
DAC
/4 and f
DAC
/8.
Rev. C | Page 42 of 60
Region C
Region C is most accurately described as a down conversion, as
the modulating carrier is −e
only the images in Region C remains. This image appears on
the real and imaginary outputs of the AD9777, 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 AD9777, 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
AD9777 and AD8345 given the complex input signal to the
AD9777 in Figure 89. The data in these graphs was taken with a
data rate of 12.5 MSPS at the AD9777 inputs. The interpolation
rate of 4× or 8× gives a DAC output data rate of 50 MSPS or
100 MSPS. As a result, 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 AD9777/
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 +f
group of negative frequencies modulated by complex −f
When looking at the real or imaginary outputs of the AD9777,
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.
DAC
jωt
/4, while Figure 93 represents a
. If viewed as a complex signal,
DAC
/4.