Texas Instruments SLAU039, User Manual

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Analog Output
2-9
AD50-EVM Design and Construction
Since most noise sources are likely to be coupled equally into both inputs the
filter in Figure 2–4b is usually the best choice (the evaluation board has
footprints to allow for either or both configurations, with the capacitor in
Figure 2–4a not connected).
The AD50 allows higher source impedances at its inputs than many
sigma-delta converters, easing the drive requirements.
The aux inputs also have antialiasing filters connected, allowing the use of
these inputs from external sources without any special filtering requirements.
The antialiasing filter components are placed as close as possible to the inputs
to the AD50 to reduce the possibility of noise pickup between the filter and the
ADC. The use of 0603 footprint surface-mount components makes this
possible.
2.7 Analog Output
The AD50 uses a pair of differential voltage outputs. The output stage needs
to convert the differential signals to a single ended output, and to attenuate
noise outside the pass-band. This filter is not a conventional reconstruction fil-
ter, since the AD50 has an integral low-pass reconstruction filter. The filter is
a 12-kHz second order low-pass filter designed for use at 20 ksps and will be
less effective at lower sampling rates. Since this filter only removes out of band
noise it will be unnecessary in many applications.
Figure 2–5. AD50-EVM Differential to Single-Ended Output Converter
_
+ 1/2 TLC2272
5 V
–5 V
100 nF
100 nF
10 k
Ω
_
+ 1/2 TLC2272
5 V
100 nF
100 nF
–5 V
10 k
Ω
10 k
Ω
10 k
Ω
2.2 nF
220 pF
22 k
Ω
5.6 k
50
Out
OUT_P
OUT_M
TLC320AD50C
5.6 k