For any of us who has worked on ADC in Microcontrollers or processors, one of the important specification we look at is the resolution. For example, take the case of MSP432P401R Microcontroller, it has a Analog-to-Digital (ADC) module with 14-bit resolution and the controller datasheet says,
"The Precision ADC module is a native 14-bit SAR analog-to-digital conversions, supports up to 16-bit
precision through software over-sampling."
For beginners, one would be wondering how come 14-bit ADC can achieve 16-bit resolution. The technique that are used to improve the resolution is:
- Oversampling
Let us look at how it can be achieved.
Oversampling is nothing but performing a higher sampling than what is required so that the additional bits for improving the resolution are covered by this sampling. This is entirely depending on the frequency components associated with the signal input. for example if Fc is the highest frequency of the analog input, then as per Nyquist theorem to achieve reproduction of the signal/measurement the sampling rate must be
Sampling Rate, Fs = 2 * Fc
Now the above is the sampling rate commonly used for the ADCs. If we want to achieve higher resolution, the sampling rate must be
Sampling Rate to achieve over sampling, Fov = F * (4^bits)
F is the highest frequency of the input signal.
bits here indicate the number of digits by which the resolution has to be increased.
For example, as mentioned in the case of MSP432 above, if we have to achieve resolution of 16-bit for a 14-bit ADC, bits = 2.
What we are doing indirectly is that we are collecting more and more samples than the desired sampling rate to get more samples within a give time there by increasing the resolution of the measurement. More number of bits in a given time higher the resolution. The firmware engineer in the code must collect these large samples and average to get the desired output.
Disadvantages:
- Giving more emphasis to ADC measurement and hence performance of the system gets affected
]]>
0 Comments