Choose Your ADC Averaging Method With Care… | Cypress Semiconductor
Choose Your ADC Averaging Method With Care…
Last week my friend Kendall Castor-Perry published an interesting article on multi-channel ADC averaging methods on Product Design and Development (www.pddnet.com). In it he discusses the options that modern integrated ADC technology gives you for optimizing conversion rate when scanning multiple channels, including the case where some channels are averaged and some are not.
The traditional method - known as sequential averaging - is to scan each channel multiple times until the averaging is complete, then move onto the next channel to repeat the process. And so on for all channels. For a given channel this results in a long delay between usable samples while the ADC scans other data. This "aperture" limits the maximum frequency that can be reliably scanned courtesy of our Swedish chum Nyquist. And the limit frequency is highly dependent on the other channels being scanned.
With the alternative method - interleaved averaging - the ADC samples each channel just once and then moves onto the next one. This repeats until the averaging is complete and can be read from the ADC. This averaging method does not suffer from the same sampling rate limitations because the samples are all taken at even intervals, rather than in bursts. Adding channels to the ADC configuration slows the overall scan rate a little but does not create the troublesome profile of bursts of samples followed by an aperture.
Kendall goes into a lot more detail than I can here. Well, to be more honest, he goes into more detail than I can regardless of where I am or who I am talking to! He touches on the limitations of ADCs with a single result register (as opposed to a register for every channel) and also discusses aliasing issues and their impact on sample frequencies. It's all good stuff and nicely explained so I definitely recommend giving the article a read.