Chapter 4
Analog Input
4-2
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On S Series devices, each channel uses its own instrumentation amplifier,
FIFO, multiplexer (mux), and A/D converter (ADC) to achieve
simultaneous data acquisition. The main blocks featured in the S Series
analog input circuitry are as follows:
•
Mux
—By default, the mux is set to route AI signals to the analog front
end. When you calibrate your device, the state of the mux switches.
You can manually switch the state of the mux to measure AI GND.
•
Instrumentation Amplifier
—The instrumentation amplifier can
amplify or attenuate an AI signal to ensure that you get the maximum
resolution of the ADC. Some S Series devices provide programmable
instrumentation amplifiers that allow you to select the input range.
•
Analog Trigger
—
(NI 6124 Only)
For information about the trigger
circuitry of S Series devices, refer to the
section.
•
Filter
—The filter on these S Series devices minimizes high frequency
noise and some attenuating signals by 3 dB at 2 MHz.
•
ADC
—The analog-to-digital converter (ADC) digitizes the AI signal
by converting the analog voltage into a digital number.
•
AI Timing Signals
—For information about the analog input timing
signals available on S Series devices, refer to the
section.
•
Isolation Barrier and Digital Isolators
—
(NI 6154 Only)
The digital
isolators across the isolation barrier provide a ground break between
the isolated analog front end and the chassis ground. For more
information about isolation and digital isolators, refer to the
Isolation and Digital Isolators
.
•
AI FIFO
—A large first-in-first-out (FIFO) buffer, located inside the
FPGA, holds data during A/D conversions to ensure that no data is lost.
S Series devices can handle multiple A/D conversion operations with
DMA, interrupts, or programmed I/O.
Analog Input Terminal Configuration
S Series devices support only differential (DIFF) input mode. The channels
on S Series devices are true differential inputs, meaning both positive and
negative inputs can carry signals of interest. For more information about
DIFF input, refer to the
Connecting Analog Input Signals
section, which
contains diagrams showing the signal paths for DIFF input mode.
