HP 54750A, Руководство пользователя, Страница: 429 / 478

How the Instrument W orks
System Architecture
The major plug-in module hardware components
Sampler The sampler consists of a diode gate and sampling capacitor . The incoming
signal is applied to the input of the diode gate , which is normally biased
o. When a trigger event occurs , the pulse lter produces a pulse which
momentarily forward biases the gate and allows the input signal to charge the
capacitor . On an optical module , the O/E conversion and SONET/SDH ltering
occur ahead of the sampler .
IF AMP The IF amplier senses the voltage on the sampling capacitor and conditions
it in preparation for digitizing in the A/D converter .
T rigger input The plug-in's trigger input passes the trigger signal directly into the
mainframe . No trigger signal conditioning occurs within the plug-in.
Pulse lter The function of the pulse lter is to transform the low repetition rate trigger
pulse from the mainframe into a narrow impulse that drives the sampler . The
width of this impulse must be as narrow as possible because it directly aects
the bandwidth of the vertical channel.
Interface circuitry The plug-in's interface circuitry accepts commands from the system
microprocessor to control such module functions as IF gain, sampler
bandwidth, and optical channel bandwidth. Non-volatile RAM within the
module provides the system microprocessor with module cal factors , as well
as information on the type of plug-in installed.
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