Sampling&ADC

You need to transform analog input from the real world to something digestible to the digital world.

Some definition:

• Signal to noise ratio: \(\hbox{SNR} = {P_\hbox{signal}\over P_\hbox{noise}}\)
• Effective number of bits: indicated as ENOB

this holds (calculation) $$\hbox{SNR}(db) = 6.02\cdot\hbox{ENOB} + 1.76$$

Nyquist-Shannon sampling theorem

Signals that differs of \({1\over T}\) are sampled the same

• Sampling: What Nyquist Didn’t Say, and What to Do About It

Oversampling and decimation

In same cases you can improve the resolution of your ADC of \(n\) bits simply summing together \(f_\hbox{oversampling} = 4^n \cdot f_{\hbox{sampling}}\) and then scaling by a factor of \(s = 2^n\). This is possible if the following assumptions hold

• the signal of interest should not vary significantly during a conversion
• there should some noise in the signal with amplitude at least 1 LSB

Links

• Getting the most out of the SAM D21's ADC
• AVR121: Enhancing ADC resolution by oversampling
• AN118: IMPROVING ADC RESOLUTION BY OVERSAMPLING AND AVERAGING
• Understand SINAD, ENOB, SNR, THD, THD + N, and SFDR so You Don't Get Lost in the Noise Floor