max5851 Maxim Integrated Products, Inc., max5851 Datasheet - Page 15

• Manufacturer Part Number: max5851
• Description: Max5851 Dual, 8-bit, 80msps, Current-output Dac
• Manufacturer: Maxim Integrated Products, Inc.

The MAX5851 exhibits excellent dynamic performance
to synthesize a wide variety of modulation schemes,
including high-order QAM modulation with OFDM.
Figure 7 shows a typical application circuit with output
transformers performing the required differential-to-
single-ended signal conversion. In this configuration,
the MAX5851 operates in differential mode, which
reduces even-order harmonics, and increases the
available output power.
Figure 8 shows the MAX5851 output operating in differ-
ential, DC-coupled mode. This configuration can be
used in communication systems employing analog
quadrature upconverters and requiring a baseband
sampling, dual-channel, high-speed DAC for I/Q syn-
Figure 7. Application with Output Transformer (Coilcraft
TTWB3010-1) Performing Differential-to-Single-Ended Conversion
8
8
DA0–DA7
DB0–DB7
Differential-to-Single-Ended Conversion
Differential DC-Coupled Configuration
AGND
AV
DD
DGND
DV
MAX5851
MAX5851
Applications Information
DD
1/2
1/2
CGND
Dual, 8-Bit, 80Msps, Current-Output DAC
CV
______________________________________________________________________________________
DD
OUTPA
OUTNA
OUTPB
OUTNB
50Ω
100Ω
50Ω
50Ω
100Ω
50Ω
SINGLE ENDED
SINGLE ENDED
V
V
OUTA
OUTB
,
,
thesis. In these applications, information bandwidth can
extend from 10MHz down to several hundred kilohertz.
DC-coupling is desirable to eliminate long discharge
time constants that are problematic with large, expen-
sive coupling capacitors. Analog quadrature upcon-
verters have a DC common-mode input requirement of
typically 0.7V to 1.0V. The MAX5851 differential I/Q out-
puts can maintain the desired full-scale level at the
required 0.7V to 1.0V DC common-mode level when
powered from a single 2.85V (±5%) supply. The
MAX5851 meets this low-power requirement with mini-
mal reduction in dynamic range while eliminating the
need for level-shifting resistor networks.
Grounding and power-supply decoupling strongly influ-
ence the MAX5851 performance. Unwanted digital
crosstalk can couple through the input, reference,
Figure 8. Application with DC-Coupled Differential Outputs
8
8
DA0–DA7
DB0–DB7
AGND
AV
DD
DGND
DV
MAX5851
MAX5851
Power Supplies, Bypassing,
DD
1/2
1/2
CGND
CV
DD
Decoupling, and Layout
50Ω
50Ω
50Ω
50Ω
OUTPA
OUTNA
OUTPB
OUTNB
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