AD9773BSVRL Analog Devices Inc, AD9773BSVRL Datasheet - Page 42

• Manufacturer Part Number: AD9773BSVRL
• Description: IC,D/A CONVERTER,DUAL,12-BIT,CMOS,TQFP,80PIN
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9773BSVRL

• Rohs Status: RoHS non-compliant
• Settling Time: 11ns
• Number Of Bits: 12
• Data Interface: Serial, SPI™
• Number Of Converters: 2
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 410mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 80-TQFP Exposed Pad, 80-eTQFP, 80-HTQFP, 80-VQFP
• For Use With: AD9773-EBZ - BOARD EVALUATION AD9773

AD9773
The complex carrier synthesized in the AD9773 digital modu-
lator is accomplished by creating two real digital carriers in
quadrature. Carriers in quadrature cannot be created with the
modulator running at f
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 AD9773 by +e
complex signal described previously, again with positive fre-
quency components only, modulated in the AD9773 by −e
The analog quadrature modulator after the AD9773 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 AD9773, 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 AD9773, Region B appears in the spectrum.
However, on the output of the quadrature modulator, Region B
is rejected.
jωt
.
jωt
. Regions C and D are the result of the
DAC
/2. As a result, complex modulation
DAC
/4 and f
DAC
/8.
jωt
.
Rev. D | Page 42 of 60
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 AD9773, 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 AD9773, 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 AD9773
and AD8345 given the complex input signal to the AD9773 in
Figure 89. The data in these graphs was taken with a data rate of
12.5 MSPS at the AD9773 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
AD9773/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 AD9773,
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, only
DAC
/4.