UG-132 Datasheet, PDF (4/8 Pages) Analog Devices – Differential Amplifier Evaluation Board for Single

UG-132
EVALUATION BOARD HARDWARE
POWER SUPPLIES
Power is applied to the board through test pins +VS and −VS
(see Figure 3). The board accommodates single or dual supplies.
For single-supply operation, connect the negative supply to the
ground plane.
It is very important that the power supply pins of the device
under test (DUT) have broadband decoupling circuitry. The
board layout facilitates this with footprints for a 0508 ceramic
capacitor C1 and C2) on each supply. Bulk decoupling is
provided by C3 and C4; 10 µF tantalum capacitors are
recommended.
FEEDBACK NETWORKS AND INPUT/OUTPUT
TERMINATIONS
R1/RG and R2/RF comprise the upper resistive feedback loop
(see Figure 3), and R3/RG and R4/RF compose the lower
feedback loop. To minimize summing node capacitances, the
ground plane under and around Pin 1 and Pin 8 of the DUT
(see Figure 3) and the copper that connects to them have been
removed.
R5 and R6 are included as input termination resistors for applica-
tions that have single-ended inputs.
Evaluation Board User Guide
VOCM INPUT
An external voltage can be applied to VOCM via J6 (referenced to
the ground plane of the board). In ADC driving applications, it
is convenient to apply the ADC dc reference voltage output
directly to J6. The R11 component position can be used for
both resistors and capacitors. A 0.1 μF capacitor is used in
normal applications to provide bypassing for the dc voltage
applied to the VOCM pin.
It is also possible to drive the VOCM input from an external ac
source. In this case, omit R11 or reduce it to a value that allows
the desired signal to be passed.
COMMON-MODE VOLTAGE
The internal common-mode feedback loop used in the differen-
tial drivers forces the output common-mode voltage to be equal
to the voltage applied to the VOCM input, thereby providing
excellent output balance.
SMA INPUT/OUTPUT CONNECTORS
The inputs and outputs have edge-mounted SMA connectors
for convenient connection to coaxial cables. The recommended
connector type is Johnson Components™, Part Number 142-
0701-801 or equivalent.
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