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What is the function of the diode between these two operational amplifiers?

Hardware design
March 15, 2021 by Nena 310

The inverting input of the operational amplifier-1 uses a voltage of 0V <= x <= 5V, while the non-inverting input is connected to a 1k ohm potentiometer. The output is 100kOhm and 0.001uF for feedback.

This output is then connected to 10k ohms in series with a 1N4149 diode. This signal is sent through 0.1uF and 100kOhm before being used as the input of the second stage (op-amp-2).

What is the function of this diode?

All Comments

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Horatio Posted on March 15, 2021

Can you tell me what the function of this circuit is? I don't know what the output and U17 and U18 are?

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  • Nena

    Nena Posted on March 15, 2021

    This is for measuring the gas-liquid voltage, and the output is the processed gas-liquid voltage, such as blood, saline, air, etc. U17 and U18 are regarded as silicone tubes that are put into the gas-liquid. And these gas and liquid have expected values, such as saline 1.5V, blood 0.9V, air 0V, etc...

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Snow Posted on March 15, 2021

Interesting, there seems to be something similar in the design of Theremen. U17/U18 and C16/C17 will form a variable capacitor and inject current into the inverting node of the first op amp. The diode (D1) and capacitor (C19) are used to solve the interference amplitude of this "variable capacitor" and can filter out high frequency noise.

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Tomi Posted on March 15, 2021

D1 and C19 form the so-called envelope detector. This circuit is used in AM radio to demodulate the radio frequency carrier and transmit audio. Although this is not an audio signal, there should be a lot of RF.

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