Measurement Computing WBK Options - Manual (Page 27)

WBK14, Dynamic Signal Input Module 988396 WBK14, pg. 3
Programmable Low-Pass Filter, Switch-Capacitor
Most of the signal alias rejection is performed by an 8-pole Butterworth filter. This filter is implemented
with a switch-capacitor network driven by a programmable clock (timebase control). Each channel has an
independent clock whose frequency determines the 3-dB cut-off frequency of the filter. The switch-
capacitor filter provides no attenuation at the clock frequency—hence, the need for the continuous-time
low-pass filter.
Note: The Low-Pass Anti-Aliasing Filter can be bypassed to process signals with a bandwidth higher
than 100 kHz.
The External Clock input provides a path to externally control the cut-off frequency of the Low-Pass
Anti-Aliasing Filter. The input waveform can be TTL or sinusoidal, with an amplitude peak of at least
500 mV. In this mode, the cut-off frequency is set to the input frequency divided by 50.
Simultaneous Sample and Hold
All WBK14 channels are sampled simultaneously, after which the WaveBook measures each output at
1 µs/channel until all channels are digitized. The time-skew between sampling on all channels (up to 72)
is 150 ns, regardless of the number of WBK14s attached to the WaveBook.
When using WaveBook with an SSH channel enabled, the per-channel sample rates are
reduced. The rate reduction is the same as that which would occur if another channel
were added. The per-channel rate (with SSH enabled) is:
1 MHz / (n+1), where n is the number of active channels.
Excitation Source
The excitation source includes a sine/random waveform generator, a programmable gain amplifier (PGA), a
DC-level DAC, and a phase-lock loop (PLL). The PLL is used to synthesize the frequency of a fixed-
amplitude sine wave and control the bandwidth of the random signals. The PGA conditions the signal
amplitude to a value between 0 V to 5 V peak. The DC level of the signal is varied independently of signal
amplitude by a software-controlled DAC from -5 V to +5 V. The DC level of the excitation signal can be
used to balance static loads, while the AC signal provides the dynamic excitation.
Calibration
WBK14 is calibrated digitally, eliminating the need for all potentiometers and manual adjustments.
WaveCal, a provided Windows-based program, simplifies the calibration process.
Reference Note:
The calibration program is detailed in the
WaveCal Document Module .