AD9750 Analog Devices, AD9750 Datasheet - Page 17

• Manufacturer Part Number: AD9750
• Manufacturer: Analog Devices

Specifications of AD9750

• Resolution (bits): 10bit
• Dac Update Rate: 125MSPS
• Dac Settling Time: 35ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Par

It is also possible to generate a QAM signal completely in the
digital domain via a DSP or ASIC, in which case only a single
DAC of sufficient resolution and performance is required to
reconstruct the QAM signal. Also available from several vendors
are Digital ASICs which implement other digital modulation
schemes such as PSK and FSK. This digital implementation has
the benefit of generating perfectly matched I and Q components
in terms of gain and phase, which is essential in maintaining
optimum performance in a communication system. In this imple-
mentation, the reconstruction DAC must be operating at a
sufficiently high clock rate to accommodate the highest specified
QAM carrier frequency. Figure 37 shows a block diagram of
such an implementation using the AD9750.
REV. 0
FREQUENCY
CARRIER
Q DATA
I DATA
12
12
12
Figure 37. Digital QAM Architecture
SIN
STEL-1130
STEL-1177
12
QAM
NCO
12
COS
CLOCK
Q DATA
R
2k
I DATA
INPUT
INPUT
FSADJ
SET1
REFIO
12
CLK
0.1 F
AD9750
REFIO
REFLO
Figure 36. Baseband QAM Implementation Using Two AD9750s
(“Q DAC”)
(“I DAC”)
LATCHES
AD9750
AD9750
LATCHES
R
1.9k
SET2
FSADJ
DVDD
AVDD
50
ACOM
R
220
CAL
DAC
DAC
U1
U2
REFLO
SLEEP
AVDD
LPF
QOUTA
QOUTB
IOUTB
IOUTA
DCOM
AVDD
50
100W
TO
MIXER
100
100
100
C
NOTE: 500
100
FILTER
500
500
–17–
C
500
FILTER
RESISTOR NETWORK - TOMC1603-100D
500
500
AD9750 EVALUATION BOARD
General Description
The AD9750-EB is an evaluation board for the AD9750 10-bit
D/A converter. Careful attention to layout and circuit design
combined with a prototyping area allow the user to easily and
effectively evaluate the AD9750 in any application where high
resolution, high speed conversion is required.
This board allows the user the flexibility to operate the AD9750 in
various configurations. Possible output configurations include
transformer coupled, resistor terminated, inverting/noninverting
and differential amplifier outputs. The digital inputs are designed
to be driven directly from various word generators, with the
on-board option to add a resistor network for proper load ter-
mination. Provisions are also made to operate the AD9750
with either the internal or external reference, or to exercise the
power-down feature.
Refer to the application note AN-420 for a thorough description
and operating instructions for the AD9750 evaluation board.
500
500mV p-p WITH
+5V
RESISTOR NETWORK - OHMTEK ORN5000D
500
V
634
CM
=1.2V
500
0.1 F
BBIP
BBIN
BBQP
BBQN
VPBF
1.82V
SPLITTER
PHASE
AD8346
+
LOIP
LOIN
VOUT
AD9750