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User's Guide
SNOA552B–July 2011–Revised May 2013
AN-2072 LMH6522 Evaluation Board
1 General Description
The LMH6522EVAL evaluation board, Figure 1, is designed to aid in the characterization of Texas
Instruments High Speed LMH6522 Digital Controlled Variable Gain Amplifier (DVGA).
Use the evaluation board as a guide for high frequency layout and as a tool to aid in device testing and
characterization.
2 Basic Operation
The LMH6522 DVGA has differential inputs and differential outputs. The evaluation board has been
designed to easily interface with 50Ω single ended test equipment. The LMH6522EVAL evaluation board
is shipped with input and output transformers installed to convert the DVGA differential inputs and outputs
to single ended signal paths. As built, the signal path uses the IN+ and OUT− marked connectors. The
IN− and OUT+ signal paths are grounded. The signal paths are fully symmetrical.
To preserve proper bias voltages there are DC blocking capacitors on both the input and output signal
traces. The input pins of the LMH6522 will self bias to approximately mid supply (2.5V). The output pins
need to be biased to near ground potential. Inductors are installed on the evaluation board to provide
proper output biasing. The bias current is approximately 36 mA per output pin. Capacitors between the
amplifier and the output transformer will prevent offset currents from flowing through the transformer
primary coil. Many transformers will show increased distortion products when there is a DC current flowing
through the primary coil.
Figure 1. LMH6522EVAL Evaluation Board
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SNOA552B–July 2011–Revised May 2013 AN-2072 LMH6522 Evaluation Board
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