Figure 6. Using the MAX5186/MAX5189 for I/Q Signal Reconstruction
Grounding and Power-Supply Decoupling
Grounding and power-supply decoupling strongly influ-
ence the MAX5186/MAX5189’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 SFDR. In addition, electromagnetic interference
(EMI) can either couple into or be generated by the
MAX5186/MAX5189. Therefore, grounding and power-
supply decoupling guidelines for high-speed, high-fre-
quency applications should be closely followed.
First, a multilayer printed circuit (PC) board with sepa-
rate ground and power-supply planes is recommend-
ed. High-speed signals should be run on controlled
impedance lines directly above the ground plane.
Since the MAX5186/MAX5189 have separate analog
and digital ground buses (AGND and DGND, respec-
tively), the PC board should also have separate analog
and digital ground sections with only one point con-
necting the two. Digital signals should run above the
digital ground plane, and analog signals should run
above the analog ground plane. Digital signals should
be kept far away from the sensitive analog reference
and clock input.
Both devices have two power-supply inputs: analog
V
DD
(AV
DD
) and digital V
DD
(DV
DD
). Each AV
DD
input
should be decoupled with parallel 10µF and 0.1µF
ceramic-chip capacitors. These capacitors should be
as close to the pin as possible, and their opposite ends
should be as close to the ground plane as possible.
The DV
DD
pins should also have separate 10µF and
0.1µF capacitors adjacent to their respective pins. Try
to minimize analog load capacitance for proper opera-
tion. For best performance, it is recommended to
bypass CREF1 and CREF2 with low-ESR 0.1µF capaci-
tors to AV
DD
.
The power-supply voltages should also be decoupled
with large tantalum or electrolytic capacitors at the
point they enter the PC board. Ferrite beads with addi-
tional decoupling capacitors forming a pi network can
also improve performance.
Chip Information
TRANSISTOR COUNT: 9464
SUBSTRATE CONNECTED TO AGND
