Design Considerations:
Blood pressure monitors can use
Korotkoff, Oscillometry, or Pulse Transit Time methods to measure blood
pressure. They employ a pressure cuff, pump, and transducer to measure
the blood pressure and heart rate in three phases: Inflation,
Measurement, and Deflation. They include an LCD, memory recall,
selection buttons, power management, and USB interface.
The pressure transducer produces the
output voltage proportional to the applied differential input pressure.
The output voltages of the pressure transducer range from 0 to 40 mV,
which needs to be amplified so that the output voltage of the DC
amplifier has a range from 0 to 5V. This is why, we need a high-gain
amplifier. Then the signal from the DC amplifier will be passed on to
the band-pass filter. The DC amplifier amplifies both DC and AC
component of the signal. The filter is designed to have large gain at
around 1-4 Hz and attenuate any signal that is out of the pass band. The
AC component from filter is important for determining when to capture
the systolic/diastolic pressures and heart rate of the patient. The
final stage of the front end is an AC coupling stage, after which the
signal is sent to analog to digital converters, and digitized.
The digital measurements of pressure and
heart rate are performed by the microprocessor. Measurements results
are stored in EEPROM or FLASH memory as a data log that can be uploaded
to a PC via USB. The analog circuit is used to amplify both the DC and
AC components of the output signal of pressure transducer so that we can
use the MCU to process the signal and obtain useful information about
the patient’s health.
Block Diagram:
Source: Texas Instruments
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