Hello!
I designed a PCB trying to read from a sensor. The signal is being modulated to three tones, one at 500Hz, one at 800Hz, and one at 1.1KHz The one at 800 Hz is about 40dB higher than the other two. The information I care about is their individual amplitude. I am using an ADC to sample the data, and then FFT to get the spectrum. I tried to use a notch filter to suppress the peak at 800Hz. I followed my text book to design a 6th order high pass and a 6th order low pass and then summed the outputs to create a notch filter. The simulation worked fine on LTSPICE, I have a notch of 34dB at 800 Hz.
The problem comes when I actually make this into a PCB implementation. The circuit uses two OPA4209 opamps and capacitors and resistors. The output of the circuit looks like simulation except that the 800Hz tone slowly increases its amplitude over time. From my observation, the rate of change is decreasing exponentially.
Does anyone has knowledge of what might be the source of this behavior?
I designed a PCB trying to read from a sensor. The signal is being modulated to three tones, one at 500Hz, one at 800Hz, and one at 1.1KHz The one at 800 Hz is about 40dB higher than the other two. The information I care about is their individual amplitude. I am using an ADC to sample the data, and then FFT to get the spectrum. I tried to use a notch filter to suppress the peak at 800Hz. I followed my text book to design a 6th order high pass and a 6th order low pass and then summed the outputs to create a notch filter. The simulation worked fine on LTSPICE, I have a notch of 34dB at 800 Hz.
The problem comes when I actually make this into a PCB implementation. The circuit uses two OPA4209 opamps and capacitors and resistors. The output of the circuit looks like simulation except that the 800Hz tone slowly increases its amplitude over time. From my observation, the rate of change is decreasing exponentially.
Does anyone has knowledge of what might be the source of this behavior?