EVAL-AD7902SDZ Datasheet, PDF (11/32 Pages) Analog Devices – On-board reference

EVAL-AD7902SDZ User Guide
EVALUATION BOARD CIRCUITRY
ANALOG INPUTS
The analog inputs to the evaluation board are SMA Connectors J6
and J14. These inputs are buffered with dedicated amplifier
circuitry (U12 and U17), as shown in Figure 26 and Figure 27.
The circuit not only allows different configurations, input range
scaling, and filtering but also allows adding a dc component and
using different op amps and supplies. The analog input amplifiers
are set as unity-gain buffers by factory default. The amplifier
positive rail is driven from 7.5 V (from U13—ADP7104). The
negative amplifier rail is driven from –VS (generated by U3—
ADP2301).
The default configuration sets all op amps (U12 and U17) at
midscale, generated from a buffered reference voltage divider
(VCM).
The evaluation board is configured by factory default for providing
a pseudo differential analog input path to ADC1 and ADC2 (see
Figure 16).
For dynamic performance, an FFT test can be done by applying
a very low distortion ac source.
For low frequency testing, the audio precision source can be
used directly because its outputs are isolated. Set the outputs as
UG-608
balanced with a floating ground. The J10 and J15 connectors are
provided for balanced termination of a signal source. Different
sources can be used; however, most are single-ended sources
that use a fixed output resistance.
By default, the evaluation board uses the amplifiers as unity-gain
buffers. The noninverting input has a common-mode adjustment
that involves a 100 kΩ shunt resistor. This resistor creates a
voltage divider with the source, which must be accounted for
when using the board.
REFERENCE
An external 5 V reference (U6—ADR435) is used to supply the
ADCs directly.
SERIAL INTERFACE
The evaluation board uses the SPORT interface from the
ADSP-BF527 DSP.
Multiple AND gates (U9, U10, and U11) are used to clock and
gate the SPORT transfer to the ADC device.
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