MAX5186-MAX5189 MAXIM [Maxim Integrated Products], MAX5186-MAX5189 Datasheet - Page 12

• Manufacturer Part Number: MAX5186-MAX5189
• Description: Dual, 8-Bit, 40MHz, Current/Voltage, Simultaneous-Output DACs
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX5186/MAX5189’s low distortion supports ana-
log reconstruction of in-phase (I) and quadrature (Q)
carrier components typically used in quadrature ampli-
tude modulation (QAM) architectures where I and Q
data are interleaved on a common data bus. A QAM
signal is both amplitude and phase modulated, created
by summing two independently modulated carriers of
identical frequency but different phase (90° phase dif-
ference).
In a typical QAM application (Figure 7), the modulation
occurs in the digital domain and the MAX5186/
Dual, 8-Bit, 40MHz, Current/Voltage,
Simultaneous-Output DACs
Figure 5c. Offset Error
12
Figure 5a. Integral Nonlinearity
I/Q Reconstruction in a QAM Application
______________________________________________________________________________________
7
6
5
4
3
2
1
0
3
2
1
0
000
000
ACTUAL
OFFSET
POINT
001
IDEAL OFFSET
POINT
DIAGRAM
ACTUAL
010
001
DIGITAL INPUT CODE
DIGITAL INPUT CODE
AT STEP
001 (1/4 LSB )
011
OFFSET ERROR
(+1 1/4 LSB)
100
010
AT STEP
011 (1/2 LSB )
101
IDEAL DIAGRAM
110
011
111
MAX5189’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 carrier
frequencies and then sums both outputs to provide the
QAM signal.
Grounding and power-supply decoupling strongly influ-
ence the MAX5186/MAX5189’s performance. Unwanted
digital crosstalk may couple through the input, refer-
Figure 5d. Gain Error
Figure 5b. Differential Nonlinearity
Grounding and Power-Supply Decoupling
6
5
4
3
2
1
0
7
6
5
4
0
000
000
IDEAL DIAGRAM
100
001
GAIN ERROR
(-1 1/4 LSB)
DIGITAL INPUT CODE
IDEAL FULL-SCALE OUTPUT
DIGITAL INPUT CODE
010
101
1 LSB
011
DIFFERENTIAL
LINEARITY ERROR (+1/4 LSB)
DIFFERENTIAL LINEARITY
ERROR (-1/4 LSB)
100
110
FULL-SCALE
101
OUTPUT
ACTUAL
1 LSB
111