Measurement Computing WaveBook rev.3.0 - Manual (Page 17)

WaveBook User’s Manual 6-25-99 WaveBook Overview 1-3
WaveBook Block Diagrams and Board Layouts
Reference Notes: Pages 1-4 and 1-5 contain the functional block diagrams and board layouts for
WaveBook/512, WaveBook/512H, and WaveBook/516. Chapters 3 and 4 include block diagrams for
WBKs and DBKs, respectively. Simple board layouts have been included when considered useful.
The following block diagrams should help you to better understand the information below.
For all three models (/512, /512H, and /516), the analog input signal path proceeds as follows:
• WaveBook/512 and WaveBook/512H: Each of the 8 pairs of differential signals (one per BNC
connector) is buffered and then switched by the channel-selection multiplexer.
• The selected differential pair is then converted to a single-ended signal by the programmable gain
amplifier (PGA). The WaveBook/512 has gain factors of ×1, ×2, ×5, or ×10 (corresponding to input
ranges of 10, 5, 2, or 1 volts). The /512H gain factors are similar.
• WaveBook/516: Each of the 8 pairs of differential signals (one per BNC connector) is buffered and
applied to a differential amplifier. The output of each differential amplifier is applied to a 5 pole, low
pass filter. The 8 channels and their low pass signals are then switched by the channel-selection
multiplexer into a the programmable gain amplifier (PGA). The WaveBook/516 has gain factors of
×1, ×2, ×5, or ×10 (corresponding to input ranges of 10, 5, 2, or 1 volts).
• The amplified signal is then 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 a /512, or /516 is 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.
• The signal is then switched over to the A/D converter. For /512 and /512H units, the A/D converter
digitizes the signal to12 bits in 1 µs. For WaveBook/516, the A/D converter digitizes the signal to
16 bits in 1 µs. Note that 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 WBK10
expansion chassis).
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.
The WaveBook also 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.
The control and timing circuit and the DSP together coordinate WaveBook activities. Every sample time,
the DSP reads from the scan sequence table and 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 and then selects
the input channel, the PGA gain, the level-shifter offset, and the A/D input source. It also conveys this
information to any attached expansion units and precisely controls the A/D conversion timing.