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Power Supply PCBA
The power supply re5 V and ±12 V from the CPU and
su5 V and ±10 V to the RF and digital PCBAs. Separate linear
regulators are used for the RF and digital PCBAs to isolate noise
from the RF PCBA. +5 V is sent to the RF and digital PCBA with only
passive filtering. All of the communications between the digital
PCBA and CPU PCBA take place across the power supply PCBA
through passive connections.
Antenna PCBA
The antenna PCBA passes RF signals applied to the BNC connectors
on the module front panel to the RF PCBA. The antenna PCBA has
no other active function.
RF PCBA
The RF PCBA consists of a synthesizer for the first local oscillator
and two receivers, one for wide-band and one for narrow-band
reception. The two antenna inputs are sent to a crossover switch
that performs the diversity switching. The type of data being
received (wide or narrow) determines which receiver is used to
demodulate the PWM. The other receiver is then used to monitor the
strength of the RF signal on the other antenna to determine if
diversity switching should take place. If it is determined that the RF
signal is greater on the unused antenna input, the antennas are
switched and operations continue. High dynamic range is obtained
by using high third-order intercept mixers in the front end. The
mixers require a high-power local oscillator to maintain linearity. A
+20 dBm local oscillator is generated on board to drive the mixers.
Digital PCBA
The digital PCBA communicates with the CPU and the RF PCBAs to
perform the decision-making tasks for the receiver. Commands from
the CPU PCBA specify the frequency and type of data to be
received. The digital PCBA programs the synthesizer on the RF
PCBA to receive that frequency. It then filters the PWM signal from
the RF PCBA and synchronizes the data, ensuring that a proper
signal is being received. Once the digital PCBA confirms signal
integrity, it passes the PWM signal onto the CPU PCBA, where the
PWM signal is converted into ECG, SpO
2
, and NIBP data and sent
over the SDLC link for display.