Rainbow Electronics MAX5858 - Manual (Page 20)

MAX5858
Dual, 10-Bit, 300Msps, Current-Output DAC with
4x/2x/1x Interpolation Filters
20 ______________________________________________________________________________________
Differential DC-Coupled Configuration
Figure 9 shows the MAX5858 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-
thesis. In these applications, information bandwidth can
extend from 10MHz down to several hundred kilohertz.
DC-coupling is desirable in order to eliminate long dis-
charge time constants that are problematic with large,
expensive coupling capacitors. Analog quadrature
upconverters have a DC common-mode input require-
ment of typically 0.7V to 1.0V. The MAX5858 differential
I/Q outputs can maintain the desired full-scale frequen-
cy spectrum at the required 0.7V to 1.0V DC common-
mode level when powered from a single 2.85V (±5%)
supply. The MAX5858 meets this low-power require-
ment with minimal reduction in dynamic range while
eliminating the need for level-shifting resistor networks.
Power Supplies, Bypassing,
Decoupling, and Layout
Grounding and power-supply decoupling strongly influ-
ence the MAX5858 performance. Unwanted digital
crosstalk can couple through the input, reference,
power-supply, and ground connections, which can
affect dynamic specifications, like signal-to-noise ratio
or spurious-free dynamic range. In addition, electro-
magnetic interference (EMI) can either couple into or
be generated by the MAX5858. Observe the grounding
and power-supply decoupling guidelines for high-
speed, high-frequency applications. Follow the power
supply and filter configuration to realize optimum
dynamic performance.
Use of a multilayer printed circuit (PC) board with sepa-
rate ground and power-supply planes is recommend-
ed. Run high-speed signals on lines directly above the
ground plane. The MAX5858 has separate analog and
digital ground buses (AGND, CGND, and DGND,
DA0–DA9
10
MAX5858
1/2
50 Ω
100 Ω
50 Ω
OUTPA
OUTNA
V OUTA ,
SINGLE ENDED
DB0–DB9
10
MAX5858
1/2
50 Ω
100 Ω
50 Ω
OUTPB
OUTNB
V
OUTB
,
SINGLE ENDED
CV DD DV DD AV DD
CGND DGND AGND
Figure 8. Application with Output Transformer Performing
Differential to Single-Ended Conversion
DA0–DA9
10
MAX5858
1/2
1/2
50 Ω
50 Ω
CV DD DV DD AV DD
CGND DGND AGND
OUTPA
OUTNA
DB0–DB9
10
MAX5858
50 Ω
50 Ω
OUTPB
OUTNB
Figure 9. Application with DC-Coupled Differential Outputs