Blood pressure sensor circuit and filtering and amplification circuit

As shown in the figure below, this circuit uses BP01 pressure sensor and MAX4472 operational amplifier. BP01 pressure sensor is specially designed for detecting blood pressure and is mainly used in portable electronic blood pressure monitors. It uses precision thick film ceramic chip and nylon plastic package, with high linearity, low noise and low external stress. It adopts internal calibration and temperature compensation to improve the measurement accuracy, stability and repeatability. Within the full range, the accuracy is ±1% and the zero offset is no more than ±300μV. MAX4472 is a low-power amplifier chip integrated with four operational amplifiers from MAXIM. In this system, the internal integrated operational amplifier A is connected to the constant current source to provide a constant current for the pressure sensor. The operational amplifier B, operational amplifier C and operational amplifier D form a differential input and single-ended output amplifier circuit, which is directly input into ADC0 to monitor the DC component of blood pressure.

Filter and amplifier circuit
As shown in the figure below, the circuit consists of two parts: filtering and amplification. Among them, MAX267 is an integrated filter produced by MAXIM, which can form low-pass, band-pass, high-pass, etc. It is flexible to use and its performance is far better than the filter circuit composed of integrated operational amplifiers.

MAX4471 is a low-power amplifier from MAXIM. MAX9028 is a low-power comparator from MAXIM. The filter circuit uses MAX267 to form a bandpass filter (allowing 0.8-38Hz signals to pass through), filtering out the DC component and power supply in the signal, as well as the high-frequency noise and power frequency interference caused by the friction between the skin and the cuff, and then further amplifying it through MAX4471 to obtain a voltage signal matched by the microcontroller, which enters ADC2 to monitor the AC component of blood pressure. At the same time, the signal is converted into a pulse signal through the low-power comparator MAX9028 to trigger ADC1 to work.