Please help me analyze this circuit and understand the red mark. Thank you.

菜鸟①号

Please help me analyze this circuit and understand the red mark. Thank you. [Copy link]

As title

菜鸟①号

led2015

Low pass filter circuit?

gmchen

Is the highest wire in the red marked circle missing a ground?

gmchen

Cainiao No. 1 published on 2023-10-19 15:15

The red circle is a T-shaped RC network.

This network has a band-stop characteristic and is connected to the feedback circuit, so this circuit should be a band-pass filter. However, this circuit is problematic. It is estimated that the poster drew this circuit diagram in reverse according to a certain actual circuit, but it is not complete and there may be errors.

菜鸟①号

This is a circuit I drew based on someone else's. I don't understand what the problem is. Please help me improve it. Thank you.

maychang

Posted by Novice① on 2023-10-24 11:49 I drew this based on someone else's circuit. I don't understand what the problem is. Please help me improve it. Thank you

[I drew this based on someone else's circuit, and I don't understand what the problem is]

If you don't know what the circuit is supposed to achieve, there's no way to improve it.

gmchen

Novice No. 1 published on 2023-10-24 11:49 This is a circuit I drew based on someone else's. I don't understand what the problem is. Please help me improve it. Thank you.

According to the circuit analysis, it should be the photodiode that receives the signal; the first op amp is a transimpedance amplifier, which converts the current signal of the diode into a voltage signal; the second op amp is a bandpass filter, which removes the noise in the signal.

Since that op amp is powered by a single power supply, the anode of the diode should be connected to near the VCC/2 level (signal ground). Similarly, the non-inverting input of the second op amp should be connected to the signal ground through a resistor, and the other end of the resistor (R21) between the two capacitors in the T-shaped network in the red circle should also be connected to the signal ground.

These three points are the top line in the diagram. So that line should be connected to the output of an op amp, and that op amp is the signal generator. The diagram is not complete yet, so the author should check it again.

gmchen

That’s it for circuit analysis.

As for improvement, I don't know the specific purpose, nor do I know what problems exist now. There is no way to talk about it.