AD8031ARTZ datasheet(11/32 Pages) AD

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EVAL-AD7903SDZ User Guide

UG-609

Rev. 0 | Page 11 of 32

EVALUATION BOARD CIRCUITRY

ANALOG INPUTS

The analog inputs to the evaluation board are SMA Connectors J6,

J7, J10, and J15. These inputs are buffered with dedicated amplifier

circuitry (U12, U14, U16, 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, U14, U16, and

U17) at midscale, generated from a buffered reference voltage

divider (VCM).

The evaluation board is configured by factory default for providing

a 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 for

a balanced and floating ground. 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 49.9 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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