Xltek EMU128 Headbox
User & Service Manual
18
Theory of Operation
Introduction
This section describes the theory of operation of the 128-channel EEG, Model
EMU128-S. The initial discussion is primarily signal-flow oriented. Detailed board-level
theory is provided later in this section.
System Overview
Features of the EMU128-S system:
The EMU128-S performs the basic function of a digital EEG front end.
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Provides a Breakout Box to connecting patient electrodes.
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Amplifies and digitizes the electrode signals.
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Transmits the digitized waveforms to a NeuroWorks computer.
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Allows selection of reference signal.
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Provides internally-generated test signals (sine and square) for user assessment of
equipment performance.
•
Allows a technologist to apply a stimulus from an external stimulator to any pair of
electrodes.
•
Maintains continuous signal monitoring while relay closures connect the stimulus to
the selected electrode pair.
Components of the Communications Link:
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Digitized waveforms are transmitted to the computer as synchronous serial data,
using three differential pairs: Clock, Data and Frame Sync.
•
Commands and replies are handled with a much slower asynchronous link (UART),
with one differential pair in each direction.
Power Sources to the Headbox:
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12VDC from the computer power supply is used for the communications interface
only. Most of the Headbox is powered by 12VAC 40KHz, generated by the XLTEK
Headbox Interface Card in the computer ISA slot or one of the PCI slots.
•
For this modular design, four 32-channel groups (identical to the boards used in the
XLTEK EEG32) are plugged into an Analog Back Plane PCB and a Digital
Motherboard PCB to function as a system.
