Datasheet

MAX5180/MAX5183
Dual, 10-Bit, 40MHz, Current/Voltage
Simultaneous-Output DACs
12 ______________________________________________________________________________________
I/Q Reconstruction in a QAM Application
The MAX5180/MAX5183’s low-distortion supports ana-
log reconstruction of in-phase (I) and quadrature (Q)
carrier components typically used in QAM (quadrature
amplitude modulation) architectures where I and Q
data are interleaved on a common data bus. A QAM
signal is a carrier frequency that is both amplitude and
phase modulated, and is created by summing two
independently modulated carriers of identical frequency
but different phase (90° phase difference).
In a typical QAM application (Figure 6), the modulation
occurs in the digital domain and the MAX5180/
MAX5183’s dual DACs may be used to reconstruct the
analog I and Q components.
The I/Q reconstruction system is completed by a quad-
rature modulator that combines the reconstructed I and
Q components with in-phase and quadrature phase
carrier frequencies, then sums both outputs to provide
the QAM signal.
Grounding and Power-Supply Decoupling
Grounding and power-supply decoupling strongly influ-
ence the MAX5180/MAX5183’s performance. Unwanted
digital crosstalk may couple through the input, refer-
ence, power-supply, and ground connections, which
may affect dynamic specifications like signal-to-noise
ratio or spurious-free dynamic range. In addition, elec-
tromagnetic interference (EMI) can either couple into or
be generated by the MAX5180/MAX5183. Therefore,
AGNDDGND
OUT1P
CREF2
CREF1
OUT1N
OUT2P
OUT2N
0.1
µ
F
0.1
µ
F
0.1
µ
F
AV
DD
AV
DD
AV
DD
R
SET
**
*400
Ω
RESISTORS INTERNAL TO MAX5183 ONLY.
**MAX5180 ONLY
MAX5180
MAX5183
10
µ
F
3V
3V
0.1
µ
F
0.1
µ
F
CLK
REFR
REFO
D0–D9
10
µ
F
400
Ω
*
400
Ω
*
5V
5V
-5V
402
Ω
402
Ω
402
Ω
DV
DD
402
Ω
OUTPUT1
REN
400
Ω
*
400
Ω
*
-5V
402
Ω
402
Ω
402
Ω
402
Ω
OUTPUT2
MAX4108
MAX4108
Figure 5. Differential to Single-Ended Conversion Using a Low-Distortion Amplifier