Rainbow Electronics MAX1213 - Manual (Page 16)

MAX1213
1.8V, 12-Bit, 170Msps ADC for
Broadband Applications
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To further enhance THD and SFDR performance at
high-input frequencies (>100MHz), a second trans-
former (
Figure 8) should be placed in series with the
single-ended-to-differential conversion transformer.
This transformer reduces the increase of even-order
harmonics at high frequencies.
Single-Ended, AC-Coupled Analog Inputs
Although not recommended, the MAX1213 can be used
in single-ended mode (
Figure 9). Analog signals can be
AC-coupled to the positive input INP through a 0.1µF
capacitor and terminated with a 49.9Ω resistor to AGND.
The negative input should be reverse terminated with
24.9Ω resistors and AC-grounded with a 0.1µF capacitor.
Grounding, Bypassing, and
Board Layout Considerations
The MAX1213 requires board layout design techniques
suitable for high-speed data converters. This ADC pro-
vides separate analog and digital power supplies. The
analog and digital supply voltage pins accept input
voltage ranges of 1.7V to 1.9V. Although both supply
types can be combined and supplied from one source,
it is recommended to use separate sources to cut down
on performance degradation caused by digital switch-
ing currents, which can couple into the analog supply
network. Isolate analog and digital supplies (AV
CC and
OV CC ) where they enter the PC board with separate
networks of ferrite beads and capacitors to their corre-
sponding grounds (AGND, OGND).
AGND OGND
D0P/N–D11P/N
AV CC
INP
INN
OV CC
12
MAX1213
0.1µF
25Ω
25Ω
0.1µF
ADT1-1WT ADT1-1WT
10Ω
10Ω
SINGLE-ENDED
INPUT TERMINAL
AGND OGND
D0P/N–D11P/N
AV CC
INP
50Ω
25Ω
INN
OV CC
12
MAX1213
0.1µF
SINGLE-ENDED
INPUT TERMINAL
0.1µF
Figure 8. Analog Input Configuration with Back-to-Back Transformers and Secondary-Side Termination
Figure 9. Single-Ended AC-Coupled Analog Input Configuration