ADC speed and resolution !

Hi guys,

i have a question about the relation of the speed and the resoultion of the ADC. I know high speed ADC normally has a low resolution and vice versa. for example sigma/delta and SAR have a high resolution but low speed. the pipeline ADC has a high speed but low resolution.

Thanks

This taxonomy should be much more flexible if you ask me.

Oversampling ADC's have high resolution but more important they shape the noise. They do not necessarily offer high resolution also. They are sometimes used as parts of an integrated circuit, like temperature measuring and so. They are kind of the best fit for low speed, low power, low area considerations.

SAR ADC's offer the most basic integrated circuit solution to A to D conversion. But there are over 50 MSPS SAR ADC's around. Fujitsu's 56 GSPS ADC uses time interleaved SAR ADC's.

Pipeline ADC's offer high speed but if you can design it well with enough linearity for each sub ADC you can also have a high resolution. As far as I know 14 bit Pipeline ADC's are available.

I would suggest you to go to the websites of Analog Devices and Linear Tech (No offense to anyone, I said so because they are the marketshare leader.) and check out speed and architecture. These two companies give the most detailed datasheets I've ever read. They explain functionality in detail so in short they teach a lot.

one thing that might help understanding the relation between speed and resolution is to know why this trade off happened in the first place. in the beginning, an ADC was simply a flash ADC where the thermometer code that represents the input signal was produced in one conversion cycle, meaning it was very fast, the problem however is as the resolution increases, the number of comparators doubled for every bit and the analog value for the LSB kept getting lower and lower. this prompted the need for ways to increase the resolution while sacrificing the speed. in other words instead of getting the output word at once, or in one cycle, the conversion happens either in many steps, such as pipelined structures, or by getting the average of the signal such as sigma delta.

i hope this helps