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Optocoupler + Schmitt Trigger problem

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ranaya

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Hi all......

Im looking for a circuit to interface high frequency pulses to the MCU with digital isolation. So I use an opto coupler with a schimitt trigger like this.

optpop.JPG

yellow - input square wave
green - opto o/p
blue - trigger o/p

But when the pulse frequency increases, opto output become a sine shape, and shcmitt trigger output ontime pulse width get increases like shown in above simulation. Real circuit showed the same result ! Is there a way to avoid this problem and to improve the frequency measurement ?

Thank You
 

chuckey

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ADI_iCoupler

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An alternate approach to the optocouplers in this design would be a digital isolator. Digital Isolators are a more modern alternative to optocouplers, offering improved performance with lower power dissipation. They’re also much easier to implement in a design since the inputs and outputs use standard digital logic. Standard digital isolators have different numbers of input and output channel combinations and can operate up to 150Mbps. Specialized products also exist for specific serial interfaces, such as USB and I2C.

You can see the entire digital isolator product line available from Analog Devices at our web site: https://www.analog.com/en/interface/digital-isolators/products/index.html
 

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