Hi everyone!
I am using the Arduino GIGA R1 WiFi for DSP experiments. I recently noticed small, negative spikes on the A0 input. For this image I connected 1.65 V (2 x 10k voltage divider from 3V3 rail) to A0. I sampled the input at a frequency of 96 kS/s. Which is about the frequency that these spikes seem to appear.
I would assume that these spikes are caused by the ADCs sample/hold capacitor being charged. If that's the case, am I further right to assume that a low-impedance buffer (opamp, etc.) would be recommended to be able to supply a sufficient amount of charge to the ADCs s&h cap? I've been doing DSP experiments using the GIGA and just now noticed these spikes. They of course propagate into the output signal (garbage in, garbage out) when sampling relatively low-voltage signals directly from a guitar.
Therefore, I was thinking to use an OpAmp to scale the input voltage so that the full dynamic range of the ADC can be utilized.