Runic‘s OP Amp RS8538and RS622, Low-Consumption LDO RS3236 Apply in Electronic Blood-Pressure Meter

The portable electronic Blood-Pressure Meter gets rid of the traditional Mercury Blood-Pressure Meter, is easier for the user to use, and the measurement result is displayed directly. The usual way is to use the oscillographic method to measure blood pressure indirectly by establishing the relationship between systolic pressure, diastolic pressure, average pressure, and cuff pressure oscillation wave, which has the characteristics of high efficiency and non-invasive.

Through inflated cuff by an Air, Booster pump compresses the arm's arteries,  then the arm is decompressed linearly by an electronically controlled air release valve, during which the blood in the blood vessels begins to flow and produce a certain shock wave after being detected by the piezoresistive sensor and then which can measure the systolic, average and diastolic blood pressure of the human body.

Runic is a High- tech company with high-performance analog signal chain design capabilities, Runic product lines such as OP Amps, Comparator,  Analog Switch, LDO, etc. Can match very well with the design of consumer medical products such as Electronic Blood-Pressure Meter.

Fig.1

In the picture above, the air hose is attached to the cuff on the side of the machine, through a piezoresistive sensor to sense the current pressure on the cuff. The essence of the piezoresistive sensor is a Wheatstone bridge, when a certain pressure is applied to the sensor, the resistance of each arm of the bridge will change. Use a Precision OP Amp RS8538 to compose a differential amplifier, which can convert the pressure signal into a voltage signal.

The oscillographic method needs to find the maximum value of the weak oscillation wave superposed in the output DC signal, that is, find the average pressure of blood pressure, and then use the corresponding relationship to find the systolic pressure and diastolic pressure. 

This means that the MCU must collect both the amplified DC voltage and the amplified AC oscillation wave after removing the DC voltage.

The typical value of RS8538 DC offset voltage is 1μV, which is very suitable for precise DC signal amplification. After the RS622 high-pass filter, the amplitude of the AC oscillation wave is amplified enough to identify, thus completing the signal sampling. Also in the system power supply, RS3236 low-power LDO can supply power for MCU or other devices.

The main parameters of Runic's high-precise OP Amp RS8538 are as below

●Wide voltage supply range: 2.5V~5.5V;

●Ultra-low offset voltage:  1μV typical,  5μVmax;

●Ultra-low temp shift:  5nV/℃ typical, 50nV/℃ max;

●Ultra-low input bias current IB:50pA;

● Gain Bandwidth: 1.6MHz;

●Quiescent current: 180μA per channel;

● 0.01Hz~10Hz noise :1.3μVpp.

The main parameters of Runic's low-noise OP Amp RS622 are as below

●Wide voltage supply range: 2.5V~5.5V;

●Low offset voltage:  0.7mV typical,  3mVmax;

●Low temp shift: 2μV/℃ typical;

●Low input bias current IB:1pA;

●Gain Bandwidth: 7MHz;

●Quiescent current: 600μA per channel;

● Noise factor:11nV/√Hz.

The main parameters of Runic's low-consumption LDO RS3236 are as below

●Wide input voltage range: 1.7V~7.5V, support 4 cells dry battery input application;

●Internal max output current limit: >500mA;

●Ultra-low quiescent current: 20μA;

●Ultra-low drop voltage :1mV/mA;

●Ultra-high PSRR: 70dB/Hz;

●Output voltage density optional: 1% or 2.5%;

●Kinds of fixed-output voltage and many packages such as SOT-23, SOT-89-3, SOT-23-5, UTDFN-1*1-4L for your choice.