Runic‘s OP Amp RS622，Analog Switch RS2105 and Low-Consumption LDO RS3236 Apply in Finger Clip Oximeter

PublishTime： 2022-12-31 Article Source：RUN-IC News

The Household portable Finger clip oximeter is highly flexible, and can quickly measure the percentage of human blood oxygen saturation (SpO2 ) and pulse rate on the basis of non-injury. Has won wide and high praise and has sold well continuously.

As the Hemoglobin in blood has different absorb abilities of red light and infrared light. Compare the Hemoglobin with oxygen (HBO2) and the Deoxygenated hemoglobin(HB), HB absorbs more red light and less infrared light, HBO2, on the other hand, absorbs less red light and more infrared. The Red and infrared LEDs are next to each other Structurally, thus can allow light to pass through in the finger-pointed single position conveniently. Light travels from one side of the finger to the other side after being picked up by a photodiode and producing a proportional voltage to it.

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 Finger clip oximeters.

The typical schematic block diagram of a portable Finger clip oximeter is as below:

Fig.1

In the picture above, the Analog switch RS2105 of Runic is used to switch red LED and infrared LED lamps, they are time-sharing and modulate at a certain frequency. The OP Amp RS321 works with the DAC inside the MCU to produce a constant current output signal, because the constant-current operation of an LED lamp can obtain a relatively stable wavelength, the emission current usually reaches tens of mA, so the on-resistance of analog switch should be less than 1Ω, and the on-resistance of RS2105 is 0.6Ω, which meets the application requirement well.

On the side of the photosensitive receiver, the OP Amp RS622 is used for the photoelectric conversion, which requires the input bias current Ib of the OP Amp to be pA-level, and the bandwidth of the OP Amp needs to be more than 5 MHZ to satisfy the fast response. The low-noise series OP Amp can better improve the resolution of the system. In the power topology, one is to use two cell dry batteries(3V) boost to 5V and then back to the system circuit to use, the other is to use a lithium battery, which can be cycled and charged for use. RUNIC low power consumption LDO RS3236 is suitable for both topologies.

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: 2uV/°C 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 Analog Switch RS2105 are as below:

●Wide voltage supply range: 1.8V~5.5V

●Low on-resistance: 0.6Ω, 1Ω max

●Output current continues:500mA

●-3dB Bandwidth：30MHz

●Quiescent current: less than 1μA

● Has MSOP-10， TDFN-3*3-10L package for your choice.

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, and UTDFN-1*1-4L for your choice.

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