SECTION 3 PRINCIPLES OF OPERATION
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3-3
Patient
Connection
BISx
Input
Protection
Amplification
and Filtering
Sigma-Delta
Modulators
FPGA
Digital
Signal
Processor
(DSP)
Serial
Comm.
BIS VISTA Monitor
Host Processor
Serial
Comm.
Color
Display
RS-232
Port
USB
Host
Port
Figure 6 - The BIS VISTA Data Flow Diagram
After passing through input protection circuits, the EEG signals are differentially amplified
and filtered to remove DC and high frequency components. The signals are digitized by
separate one bit sigma-delta analog to digital converters and sent to the Digital Signal
Processor (DSP). The DSP filters the signals and computes the processed variables. The
results are passed to the monitor for display.
3.2.1
The BISx
The BISx contains the inputs, amplifiers, and digitizers for two channels of EEG, and
contains the circuits to digitally process the EEG data and compute the processed
parameters. It has a single point connection that connects via a Patient Interface Cable (PIC)
to a BIS sensor. The sensor and PIC contain circuits for identifying them to the monitor.
This permits the monitor to configure automatically.
The BISx contains circuits for injecting self-test voltages into the amplifier inputs. It
constantly monitors the combined source impedance from the sensor electrodes and is able
to measure the individual impedance of the channel and ground electrodes.
