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4
2.0 Board Assembly
The ADC121C02XEB evaluation board comes
fully assembled and ready for use. The provided
jumpers are in their recommended locations and
suit the needs of most users. Refer to the Bill of
Materials for a description of components, to
Figure 1
for major component placement, and to
Figure 10
for the evaluation board schematic.
While the board has been populated in a manner
that is most advantageous for typical usage, the
board can be customized by adding components
to meet the user’s specific needs. The board
comes ready to use with a DC coupled input
signal (
Figure 2
). However, by adding DC bias
resistors R1 and R4 (value 4.99k
Ω
), and changing
C1 to a 1.0uF capacitor, the board can be used
with an AC coupled input signal (
Figure 3
).
Figure 2: DC Coupled Input Configuration
Figure 3: AC Coupled Input Configuration
If needed, the input can be terminated by adding
an appropriate termination resistor at R3. The
V_IN footprint (J2) has been stuffed with a single-
pin header for testing typical, slow-moving DC
input signals. An SMA footprint is also included
on the PCB and should be used for precise
dynamic performance evaluation. The Bill of
Materials (
Section 10
) lists an appropriate SMA
connector to use.
The LMP7731 Low-noise, Precision Operational
Amplifier is included on the ADC121C02XEB for
convenient buffering of the analog input. By
default, it is configured as a simple voltage
follower (
Figure 4
). Resistors R10 and R11 can
be modified to add non-inverting gain to the
circuit. Adding capacitance at C6 configures the
amplifier as a low-pass filter. To incorporate the
input buffer into the signal path, short pins 2 and 3
of JP1.
Figure 4: Input Buffer Configuration
