No. This is not AC noise. This is signal generated by oscillation of the feedback control system attempting to regulate the output DC voltage. You do not filter out this oscillation. You need to stop the oscillation in the first place.Hello everyone, perhaps i should have been more clearer,my signal is a pure DC,generated from an LM323, which is powering a micro-controller.No Vreg DC value is perfect and it will carry some noise along with it.Now i could just use a decoupling capacitor near the LM323,but by my understanding the cap here is not used to protect the signal from noise ,but to prevent it from generating noise as rapid changes in the current consumption from the Vreg occurs.
Can't i use a low pass filter here to filter out any unwanted AC noise instead,for which i need a minimum cutoff value?
No, the source of the noise is the uController itself. It is a digital device, so the noise is generated by the transient current pulses that flow in/out of its Vdd and Vss pins as its internal nodes switch. You need to store energy right across the Vdd and Vss pins (in a Bypass capacitor), with the shortest (lowest inductance) possible leads.Hello everyone, perhaps i should have been more clearer,my signal is a pure DC,generated from an LM323, which is powering a micro-controller.No Vreg DC value is perfect and it will carry some noise along with it.Now i could just use a decoupling capacitor near the LM323,but by my understanding the cap here is not used to protect the signal from noise ,but to prevent it from generating noise as rapid changes in the current consumption from the Vreg occurs.
Can't i use a low pass filter here to filter out any unwanted AC noise instead,for which i need a minimum cutoff value?
When sampling a time-varying signal with an ADC, you always need to have a low-pass filter ahead of the ADC which cuts off frequencies above half the sampling rate. See the Nyquist Theorem....
Is this same true for a varying DC,i mean for signals that would be given to an adc. I have a digital filter incorporated inside my controller, but to avoid any kind of aliasing effect ,should i have a filter before the adc samples the signal?
No, you should look at the real frequency components you are trying to measure. If there was an anti-aliasing low-pass filter with a 1Hz cutoff, would you be missing anything that is happening because the sun comes out from behind a cloud, or if you move the panel?I am trying to do both.The decoupling capacitors did the trick in the first case.The noise level is slightly lower than before.
As for the dc signal which is to be measured ,the signal is a solar panel voltage which varies throughout the day.(0 to 5v)
I have configured my controller to sample at 94.33kHz(sampling period is about 10.6us),so that means i should have a filter with a cut off frequency of about 47KHz or less?
How so,i plotted it again and i g0t the same bode plot.That will work.
I am curious, though. Your plot doesn't match the simple RC you show in the schematic?
by Jake Hertz
by Aaron Carman
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