XRD8794AB View Datasheet(PDF) - Exar Corporation

Part Name

Description

Manufacturer

XRD8794AB

XRD8794AB Application Board

Exar Corporation 

XRD8794AB

The major components supporting the A/D under test are:

1. VREF BUFFERS - A dual op amp (EL2224C) can be

used to isolate the externally supplied VRT and VRB

from the device under test and provides a low source

impedance. These buffers can be bypassed with on-

board jumpers (JP5 and JP7). Holes for optional

compensation and gain are provided.

2. ANALOG INPUT AMPLIFIER - An operational am-

plifier (AD843) is used to provide a low source im-

pedance to the A/D. Provisions are made for sum-

ming a dither signal and/or offset voltage with the in-

put.

3. DATA LATCHES - The digital output of the A/D drive

on-board quiet latches (74ACQ377) which buffer the

device under test from the external test equipment.

4. RECONSTRUCTION DAC - A simple resistor imple-

mentation of a reconstruction DAC allows for a cross

plot test at TP4. TP4 outputs an analog waveform

generated from the four LSBs taken at the outputs of

the data latches. See Cross Plot Test.

5. DIGITAL & ANALOG WORK AREAS - 100 mil

spaced holes allow configuration of additional cir-

cuitry powered from either analog or digital planes.

The work area power and ground pads are shown in

Figure 3. for both the analog and digital planes.

–15 V +15 V AVDD

AGND DGND

+5 V

Figure 3. Analog and Digital Work Area

with Power and Ground Pads

External Equipment Required

The system block diagrams (Figure 4., Figure 5., and

Figure 8.) show the external test equipment required to

perform all test and evaluation functions. These include:

1. POWER SUPPLIES - 15V and several +5V exter- 2.

nal power supplies are needed. Separate digital and

analog grounds are provided. The analog and digital

ground planes are soldered together underneath the

board. The XRD8794 substrate is common to both 3.

the digital and analog ground pins. Treat the data

converter as an analog device when considering lay-

out grounding options. Decoupling circuits are pro-

vided on the applications board, however, low noise,

low output impedance supplies are necessary for

Rev. 1.00

4

best performance. Banana connectors are used for

all power and ground connections. For best results,

twist the power supply cable pairs. This minimizes

coupling to and from unrelated sections of the setup.

CLOCK GENERATOR - A symmetrical clock signal

must be applied to the BNC coax connector labeled

CLOCK. Select a low jitter clock for best spectral re-

sults. Note the 50Ω input impedance.

REFERENCE SUPPLIES - A positive and negative

reference voltage is connected through the BNC

coax connectors labeled VRT and VRB (typically +5

and 0V respectively). The external reference volt-

ages can be configured to go through op amp buffers

or go directly to the A/D by using jumpers JP5 and

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