I beg you experts for help. In order to realize the function of heart rate detection, I built a circuit proposed by the predecessors on the PCB board. This is part of the circuit. The front operational amplifier sends the output signal to the comparator for comparison.
The problem is that when the op amp is not connected to the subsequent stage comparator, the output waveform of the op amp is correct, which is probably the following waveform:
But after connecting the comparator, the output of the op amp becomes an oscillating signal, and the frequency is also in the same order of magnitude as the above frequency. My brother speculates that the op amp is oscillating, but I have not been able to find a suitable method to solve this problem. I hope you can talk about your views on this problem. I am very grateful.
Franz Posted on October 7, 2020
Is the power decoupling of the op amp not done well?
Henrique Posted on October 7, 2020
It is recommended that you add a resistance of about 1M from the negative terminal of the comparator to the output.
It should solve your problem.
Birdie Posted on October 7, 2020
Refer to the above several points, 1. Power decoupling capacitor 2. Change the comparator to a hysteresis comparator to enhance the anti-interference ability, and add a resistor between the output terminal of the comparator and the positive terminal of the reference voltage.
