AN206 View Datasheet(PDF) - Vishay Semiconductors
Part Name
Description
Manufacturer
AN206 Datasheet PDF : 3 Pages
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AN206
Vishay Siliconix
PC
RS-232
Micro
Controller
Temperature
Oxygen
Saturation
Pulse
Rate
To Patient
Monitor
FIGURE 2. Patient Simulator Block Diagram
Design Considerations
The temperature parameter was simulated by using a discrete
resistor array and a pair of analog multiplexers as illustrated in
Figure 3. A discrete resistor value representing a known
temperature was placed between the same channel of two
analog multiplexers. Using its I/O lines, the microcontroller
simultaneously selects one of the 16 resistors. A know current
is sent through the resistor. The medical monitor reads the
voltage drop across the resistor and translates it into a
temperature reading.
Since rDS(on) affects the output voltage, in order to obtain
accurate results, it was necessary to use the multiplexers with
a low on-channel resistance. The temperature simulation
section of the design utilized the DG406, a 16-channel
multiplexer manufactured by Vishay Siliconix. Thus, it was
possible to simulate 16 discrete temperatures by using a pair
of multiplexers. The DG406 was ultimately chosen for its low
rDS(on) of approximately 40 W typical. This value was
measured and confirmed several times. To get the best results
possible, lower resistor values were used and a digital
potentionmeter array was used to get the exact resistance
required including the 40-W rDS(on).
Simulating the saturated oxygen level was accomplished
utilizing another DG406 multiplexer. An analog signal was sent
through the selected channel of the multiplexer and attenuated
in a predetermined manner. The resulting signal is then output
to the medical patient monitor modifying the saturated oxygen
parameter. Again an array of digital pots was used to
compensate for the already low on-resistance and to get the
exact resistance values desired.
R1
Digital Pots
R2
R16
DG406
DG406
www.vishay.com S FaxBack 408-970-5600
6-2
FIGURE 3. Temperature Simulation Circuit
I
VOUT to
Monitor
From mC
Document Number: 70604
10-Aug-99
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