XRD8794AB データシートの表示（PDF） - Exar Corporation
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XRD8794AB Datasheet PDF : 24 Pages
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XRD8794AB
ANALOG TESTING WITH EXTERNAL DAC
The logic output of the system can be converted back to
analog by using a high performance digital-to-analog
converter. Laboratory spectrum analyzers and
oscilloscopes can be used to measure linearity,
frequency response, harmonic distortion, noise,
intermodulation distortion, etc. These measurements can
be converted to the specifications commonly used in
specifying A/D’s dynamically. In addition to a high quality
sinewave input, the output digital-to-analog converter
must be significantly more accurate than the A/D under
test.
CROSS PLOT
An evaluation of differential linearity can be simply done
with an oscilloscope, a triangle wave generator and a low
noise DC signal source. Input BNCs are provided on the
board so this “cross plot” method can be conveniently
implemented (See Figure 8.) The oscilloscope must be
set in the X-Y display mode.
A triangle wave (500 Hz) with a peak-to-peak amplitude of
approximately 320 LSBs is supplied to the “DITHER”
input. This is attenuated by a factor of R5/R3 by the input
amplifier. The triangle wave is also used to drive the x axis
of the scope. The horizontal gain is set so that 16 divisions
are swept. Look at Test Point 4 (TP4) with the vertical
input. Set the horizontal gain at about 2 LSB per division.
Power
Supplies
Low Noise
Triangle
Wave
Generator
Clock
Generator
Oscilloscope
X Axis
Y Axis
Low Noise
Precision
DL Voltage
Source
AIN
Dither
R3
R5
VRT
VRB
Clock
AIN
TP4
R16-19
R15
4
Data
Latches
12
C
o
n
n
e
c
t
PTS o
r
DB
VRT (0-11)
VRB
AP
XRD8794AB
Rev. 1.00
Top
Reference
Bottom
Reference
Figure 8. Crossplot Setup
10
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