Mallinckrodt NELLCOR NPB-4000, Service Manual

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Section 16: MP-205 Service Manual; 044540A-0296
16-2
16.3 CIRCUIT DESCRIPTION
This section provides service personnel with an explanation of the circuit
operation for the oximetry module. The text is supported with a schematic
diagram, see Figure 17-1.
16.4 Interconnections
16.4.1
Host (Monitor) Interconnect
The monitor interface is a 14-pin dual-row header connector, JP5. This
connector includes the power supplied by the host monitor, a serial interface
port, and two hardware control lines. The power required by the oximetry
module is +5 volts (digital) and ±5 volts (analog).
Other than supply voltages provided to the module from the power supply, there
are five data signals present at the module connection to the monitor, see
Figure 17-1.
CTS*
clear to send is a logic signal (active low)
transmitted to the module by the monitor to
suspend data transmission from the module.
EXT_RESET* an asynchronous input (active low) from the
monitor to effect a reset in the oximetry module;
CR3 provides a voltage protection from the power-
on reset.
RXD
the receive data line to the oximetry module.
TXD the transmitted data line from the oximetry module;
U6 provides a buffer for this signal.
C_LOCK a hardwired timing pulse (active high) transmitted
to the oximetry module, via the host instrument,
from an external ECG monitor. The rising edge of
this pulse is used by the module to satisfy the
software requirements necessary to perform pulse
recognition using ECG as a timing reference.
NOTE: “ * ” indicates a LOW active signal.
16.5 Sensor Interconnect
The sensor interface is a 10-pin dual-row connector, JP1, located on the oximetry
module PCB.
16.6 Oxichip Circuit
At the heart of the oximetry module is the U1 Oxichip
™
integrated circuit, which
provides variable LED drive, photodetector amplification, variable gain,
demodulation, filtering, and signal conditioning for the analog-to-digital
converter (ADC) input. The
Oxichip circuit generates its own LED modulation
and photodetector demodulation timing. It requires only a single clock at
8-times the desired LED switching frequency. A block diagram of the
Oxichip
circuit is shown on Figure 17-2.
In the following discussion, parts that are internal to the Oxichip circuit are noted
with a "U1." prefix.