Measurement Computing WaveBook rev.5.3 - Manual (Page 74)

4-4 WaveBook Operation Reference 897895 WaveBook/512A, /516, /516A, /516E
Buffering, Amplifying, and Filtering Differential Signals
WaveBooks have 8 pairs of differential signals, one pair per BNC connector. Each pair of signals is
buffered and applied to a differential amplifier. The output of each differential amplifier can be applied to
a 5 pole, low pass filter. The filter and channel-selection multiplexer then switches the non-filtered and
filtered signals to a programmable gain amplifier (PGA). The amplified signal is level-shifted to locate the
desired range (within the A/D converter's fixed input range). Two offset settings are available, unipolar
and bipolar. Unipolar offset is used for sampling signals that are always positive. Bipolar offset is used
for signals that may be positive or negative. For example, when set for unipolar at a gain of ×5, the input
span is 2 volts and the amplified signal is offset so that input voltages from 0 to +2 volts can be digitized.
When set for bipolar operation, the offset is adjusted so that input voltages from -1.0 to +1.0 volts can be
digitized.
Digitizing Signals via the A/D Converter
For the WaveBook/516, /516A, and /516E, the signal is switched over to the A/D converter and digitized
to 16 bits in 1 µs. For WaveBook/512A, the signal is digitized to 12-bits in 1 µs. The A/D converter's
input can be switched to the expansion signal input, allowing the device to read one of 64 possible
expansion channels supplied by up to eight expansion modules [WBK10A, WBK14, WBK15, WBK16,
WBK17, WBK18]. The digital signal processor (DSP) processes the digitized value and corrects the value
for gain and offset errors. The DSP places the corrected result into the FIFO data buffer that holds the
samples until the PC reads the data. If the sample is used for triggering, the DSP determines if a valid
trigger event has occurred.
Using a Sample for Triggering
Low-Latency Analog or TTL-level Triggering
WaveBook includes low-latency analog or TTL-level triggering. The low-latency analog trigger detector
examines the WaveBook input channel 1 to determine if a trigger has occurred. The selected low-latency
trigger is presented to the control and timing circuit that starts the acquisition after the trigger. The TTL
trigger is taken directly from the digital I/O port. A detailed discussion of triggering begins on page 4-15.
Sync Ports
The “A” and “E” Series WaveBooks each contain two SYNC ports. With respect to each other, the units
can be scan-synchronized and triggered by connecting one of the two WaveBook SYNC ports to a SYNC
port on a second “A” or “E” Series WaveBook or to a SYNC port of a WBK40 or WBK41 module.
Additional information on synchronization begins on page 4-23.
Control, Timing, and Signal Processing
The Control-and-Timing Circuit and the Digital Signal Processor (DSP)
The Control-and-Timing Circuit and the Digital Signal Processor (DSP) work together. At each sample
time, the DSP: (a) reads from the scan sequence table, and (b) accordingly programs the Control-and-
Timing Circuit for the next sample. The Control-and-Timing Circuit waits precisely until the start of the
next sample, then selects:
the input channel
PGA gain
level-shifter offset
A/D input source
The control-and-timing circuit conveys this information to any attached expansion units and precisely
controls the A/D conversion timing.