AD9763ASTZ Analog Devices Inc, AD9763ASTZ Datasheet - Page 21

• Manufacturer Part Number: AD9763ASTZ
• Description: IC DAC 10BIT DUAL 125MSPS 48LQFP
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9763ASTZ

• Data Interface: Parallel
• Settling Time: 35ns
• Number Of Bits: 10
• Number Of Converters: 2
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 450mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Resolution (bits): 10bit
• Sampling Rate: 125MSPS
• Input Channel Type: Parallel
• Supply Voltage Range - Analog: 3V To 5.5V
• Supply Voltage Range - Digital: 2.7V To 5.5V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AD9763-EBZ - BOARD EVAL FOR AD9763
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

APPLICATIONS
USING THE AD9763 FOR QUADRATURE
AMPLITUDE MODULATION (QAM)
QAM is one of the most widely used digital modulation schemes
in digital communications systems. This modulation technique
can be found in FDM as well as spread spectrum (CDMA) based
systems. A QAM signal is a carrier frequency that is modulated
in both amplitude (AM modulation) and phase (PM modulation).
It can be generated by independently modulating two carriers of
identical frequency, but with a 90° phase difference. This results
in an in-phase (I) carrier component and a quadrature (Q)
carrier component at a 90° phase shift with respect to the I
component. The I and Q components are then summed to
provide a QAM signal at the specified carrier frequency.
A common and traditional implementation of a QAM modula-
tor is shown in Figure 42. The modulation is performed in the
analog domain where two DACs are used to generate the
baseband I and Q components. Each component is then typically
applied to a Nyquist filter before being applied to a quadrature
mixer. The matching Nyquist filters shape and limit the spectral
envelope of each component while minimizing intersymbol
interference. The DAC is typically updated at the QAM symbol
rate or possibly a multiple of it if an interpolating filter precedes
the DAC. The use of an interpolating filter typically eases the
implementation and complexity of the analog filter, a significant
contributor to mismatches in gain and phase between the two
TEKTRONICS
AWG2021
OPTION 4
WITH
IQWRT
IQCLK
IQSEL
SLEEP
NOTES
1. DAC's FULL-SCALE OUTPUT CURRENT = I
2. RA, RB, AND RL ARE THIN FILM RESISTOR NETWORKS
WITH 0.1% MATCHING, 1% ACCURACY AVAILABLE
FROM OHMTEK ORNXXXXD SERIES.
DCOM
MODE
DVDD
3.9kΩ
R
SET
FSADJ1
LATCH
LATCH
Q DAC
I DAC
AD9763
3.9kΩ
R
ACOM
Figure 43. Baseband QAM Implementation Using an AD9763 and AD8346
SET
FSADJQ
AVDD
DAC
DAC
0.1µF
Q
I
REFIO
QOUTA
QOUTB
I
I
OUTA
OUTB
OUTFS
CA
CA
.
DIFFERENTIAL
RLC FILTER
RL
RL
RL
RL
Rev. D | Page 21 of 32
LA
LA
LA
LA
RL
RL
RL
CB
CB
RL
RB
RB
RB
RB
RA
VDIFF = 1.82 V p-p
CFILTER
baseband channels. A quadrature mixer modulates the I and Q
components with the in-phase and quadrature carrier frequency
and then sums the two outputs to provide the QAM signal.
In this implementation, it is much more difficult to maintain
proper gain and phase matching between the I and Q channels.
The circuit implementation shown in Figure 43 helps improve
upon the matching between the I and Q channels, as well as
showing a path for upconversion using the AD8346 quadrature
modulator. The AD9763 provides both I and Q DACs as well as
a common reference that improves the gain matching and
stability. R
gain between the two channels. The mismatch can be attributed
to the mismatch between R
of each channel, and/or the voltage offset of the control amplifier
in each DAC. The differential voltage outputs of both DACs in
the AD9763 are fed into the respective differential inputs of the
AD8346 via matching networks.
AVDD
RA
RL = 200Ω
RA = 2500Ω
RB = 500Ω
RP = 200Ω
CA = 280pF
CB = 45pF
LA = 10µH
I
AVDD = 5.0V
VCM = 1.2V
OUTFS
RA
ASIC
DSP
OR
= 11mA
RA
0.1µF
CAL
10
10
can be used to compensate for any mismatch in
Figure 42. Typical Analog QAM Architecture
BBQP
0 TO I
BBIP
BBIN
BBQN
AD976x
DAC
DAC
OUTFS
VPBF
SPLITTER
AD8346
PHASE
FREQUENCY
CARRIER
NYQUIST
V
SET1
FILTERS
DAC
+
RL
and R
VOUT
LOIP
LOIN
RB
SPECTRUM ANALYZER
SIGNAL GENERATOR
ROHDE & SCHWARZ
SET2
AVDD
ROHDE & SCHWARZ
, effective load resistance
RA
QUADRATURE
MODULATOR
FSEA30B
0°
90°
AD8346
V
MOD
Σ
AD9763
TO
MIXER