IC compatibility

Hi everyone!

We are building a pulse oximeter for our final year project. We found this application note in Analog devices website

http://www.analog.com/en/content/photodiode_sensing_in_pulse_oximeters/fca.html

But the ICs mentioned have their supply voltage range from 5V to 16V. Other ICs in our circuit have their operating voltages in the range 3V-less than 5V. We are using a blackfin processor too.

Can you please suggest op amps similar to AD8663/AD8667/AD8669 with operating voltage in the range we require?

Thanks in advance.

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  • You can use my parametric chooser at http://www.sevensoftltd.com/OpAmp.aspx to look for suitable candidates

    Suitable devices are the OPA376, LMP7701 and LTC6240 as they are 3V parts that all exceed the AD8663 except in terms of current requirements.

    Not mentioned in the article but key to photodiode transimpedance circuits is the issue of bandwidth and stability. I don't know what bandwidth you need, but you usually need to add a feedback capacitor for stability. This compensates for the pole inside the loop caused by the photodiod capacitance, but also reduces your bandwidth. I'm guessing the signal is modulated so that ambient (environmental) light can be rejected, so you will need enough bandwidth to work at the modulation frequency.

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  • You can use my parametric chooser at http://www.sevensoftltd.com/OpAmp.aspx to look for suitable candidates

    Suitable devices are the OPA376, LMP7701 and LTC6240 as they are 3V parts that all exceed the AD8663 except in terms of current requirements.

    Not mentioned in the article but key to photodiode transimpedance circuits is the issue of bandwidth and stability. I don't know what bandwidth you need, but you usually need to add a feedback capacitor for stability. This compensates for the pole inside the loop caused by the photodiod capacitance, but also reduces your bandwidth. I'm guessing the signal is modulated so that ambient (environmental) light can be rejected, so you will need enough bandwidth to work at the modulation frequency.

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