AD9762
–18–
REV. B
REFIO
FS ADJ
IOUTA
IOUTB
CLOCK
R
SET
2k⍀*
R
CAL1
50⍀
CLOCK
U1
I-CHANNEL
50⍀**
R
LOAD
50⍀**
R
LOAD
TO
NYQUIST
FILTER
AND MIXER
REFIO
FS ADJ
IOUTA
IOUTB
CLOCK
R
SET
2k⍀*
R
CAL2
100⍀
U2
Q-CHANNEL
50⍀**
R
LOAD
50⍀**
R
LOAD
TO
NYQUIST
FILTER
AND MIXER
0.1F
REFLO
REFLO
AVDD
* OHMTEK ORNA1001F
** OHMTEK TOMC1603-50F
Figure 57. Baseband QAM Implementation Using Two
AD9762s
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
implementation, the reconstruction DAC must be operating at a
sufficiently high clock rate to accommodate the highest specified
QAM carrier frequency. Figure 58 shows a block diagram of
such an implementation using the AD9762.
50⍀
AD9762
LPF
50⍀
TO
MIXER
STEL-1130
QAM
12
COS
12
SIN
12
12
I DATA
Q DATA
12
CARRIER
FREQUENCY
12
STEL-1177
NCO
CLOCK
Figure 58. Digital QAM Architecture
AD9762 EVALUATION BOARD
General Description
The AD9762-EB is an evaluation board for the AD9762 12-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 AD9762 in any application where high
resolution, high speed conversion is required.
This board allows the user the flexibility to operate the AD9762
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
termination. Provisions are also made to operate the AD9762
with either the internal or external reference, or to exercise
the power-down feature.
Refer to the application note AN-420 “Using the AD9760/
AD9762/AD9764-EB Evaluation Board” for a thorough
description and operating instructions for the AD9762
evaluation board.
