Rainbow Electronics MAX1215 User Manual

Page 15

MAX1215

1.8V, 12-Bit, 250Msps ADC for

Broadband Applications

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To further enhance THD and SFDR performance at high
input frequencies (>100MHz), a second transformer
(Figure 8) should be placed in series with the single-
ended-to-differential conversion transformer. This trans-
former reduces the increase of even-order harmonics at
high frequencies.

Single-Ended, AC-Coupled Analog Inputs

Although not recommended, the MAX1215 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 49.9

Ω resistor to AGND.

The negative input should be reverse terminated with
24.9

Ω resistors and AC-grounded with a 0.1µF capacitor.

Grounding, Bypassing, and

Board Layout Considerations

The MAX1215 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 1.7V to
1.9V input voltage ranges. 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 switching
currents, which can couple into the analog supply net-
work. Isolate analog and digital supplies (AV

and

) 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

INP

INN

MAX1215

0.1

µF

Ω

0.1

µF

ADT1-1WT

Ω

SINGLE-ENDED

INPUT TERMINAL