Rainbow Electronics MAX107 - Manual (Page 16)

MAX107
Grounding, Bypassing,
and Board Layout
Grounding and power supply decoupling strongly influ-
ence the MAX107’s performance. At 400MHz clock fre-
quency and 6-bit resolution, unwanted digital crosstalk
may couple through the input, reference, power supply,
ground connections, and adversely influence the
dynamic performance of the ADC. In addition, the I&Q
inputs may crosstalk through poorly designed decou-
pling circuits. Therefore, closely follow the grounding
and power-supply decoupling guidelines in
Figure 9.
Maxim strongly recommends using a multilayer printed
circuit board (PC board) with separate ground and
power supply planes. Since the MAX107 has separate
analog and digital ground connections (AGND, AGNDI,
AGNDQ, AGNDR, OGNDI, and OGNDQ, respectively).
The PC board should feature separate sections desig-
nated to analog (AGND) and digital (OGND), connect-
ed at only one point. Digital signals should run above
the digital ground plane and analog signals should run
above the analog ground plane. Keep digital signals far
away from the sensitive analog inputs, reference inputs,
and clock inputs. High-speed signals, including clocks,
analog inputs, and digital outputs, should be routed on
50
Ω microstrip lines, such as those employed on the
MAX105EV kit.
The MAX107 has separate analog and digital power-
supply inputs:
• AV CC = +5V ±5%: Power supply for the analog
input section of the clock circuit.
• AV CC I = +5V ±5%: Power supply for the I-channel
common-mode buffer, pre-amp and quantizer.
• AV CC Q = +5V ±5%: Power supply for the Q-chan-
nel common-mode buffer, pre-amp and quantizer.
• AV CC R = +5V ±5%: Power supply for the on-chip
bandgap reference.
• OV CC I = +3.3V ±10%: Power supply for the I-chan-
nel output drivers and DREADY circuitry.
• OV CC Q = +3.3V ±10%: Power supply for the
Q-channel output drivers and DOR circuitry.
All supplies should be decoupled with large tantalum or
electrolytic capacitors at the point they enter the PC
board. For best performance, bypass all power sup-
plies to the appropriate ground with a 10µF tantalum
Dual, 6-Bit, 400Msps ADC with On-Chip,
Wideband Input Amplifier
16 ______________________________________________________________________________________
2k Ω AV CC
DREADY+/DREADY-
DOR+/DOR-
10k Ω
10k Ω
CM BUFFER
NYQUIST
FILTER
FROM PREVIOUS STAGE
QUADRATURE
DEMODULATOR
MAX2108
CM BUFFER
REFERENCE
PRIMARY
DATA PORT
P0I-P5I
AUXILIARY
DATA PORT
A0I-A5I
PRIMARY
DATA PORT
P0Q-P5Q
AUXILIARY
DATA PORT
A0Q-A5Q
I ADC
1:2
D
S
P
REF
2k Ω
PRE-AMP Q ADC
REF
DOR
LO
90 °
NYQUIST
FILTER
PRE-AMP
Figure 8. Typical I/Q Application