Medical Applications User Guide (pdf) - Freescale Semiconductor

ADC
Analog-to-digital converters (ADC) are one of
the most important modules on the medical
and overall electronics field. This module
allows the conversion of an analog input
into a digital value that can be processed
by a MCU or MPU. ADCs output an N-bits
value as a result of the conversion, and can
take significant amount of PCB size placed
separately. Embedded ADCs reduce PCB size
and processing efforts reducing the access
time to the result value.
DAC
The digital-to-analog converter (DAC)
generates an analog voltage depending on
the value in its input register and the module
resolution. DACs are useful in the generation of
reference voltages or as wave form generators.
Electrocardiography uses DACs for ECG
baseline adjustment.
PDB
The programmable delay block (PDB) provides
controllable delays from either an internal
or an external trigger, or a programmable
interval tick, to the hardware trigger inputs of
ADCs and/or generates the interval triggers
to DACs, so that the precise timing between
ADC conversions and/or DAC updates can
be achieved. The PDB can optionally provide
pulse outputs (pulse-outs) that are used as the
sample window in the Analog Comparator.
VREF
VREF module generates a static voltage that
can be used as a reference on an OPAMP,
DAC, ACMP or other application without
need of external regulators. Embedded VREF
modules are programmable and can reduce
the amount of external components on a PCB
eliminating the need of external regulators or
voltage dividers for VREF applications.
Table A-1: Filters for Medical Applications
Appendix
Type Circuit Cut frequency Equation
Band-pass
passive
Reject-band
passive
0.1 Hz–150 Hz
Heart operating range
40 Hz–60 Hz
Noise signal
from the line
Band-pass active 400 Hz–4 KHz
Sound wave
bounced (range
depends of the
transducer)
Low-pass active 150 Hz
Heart operating range (if
the passive filter is not
enough, use an active
filter)
High-pass filter
active
Filter Design
A lot of noise is present in biophysical signals.
To attenuate this noise, low pass filters and
high pass filters are used to amplify the small
AC components and reject DC components.
The filters allow only the useful signals, which
helps to attain a more accurate diagnosis.
These filters can be built with passives
or actives (op amps) depending on the
application, although active filters are more
effective at rejecting noise. Passive filters are
more cost-effective and are suitable in some
cases. Sometimes the MCU does not have a
DAC. This can be built by the PWM module
and external low pass filter to convert digital
data to analog data.
Some medical applications
Not specific
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