Does External ADC slows down microcontroller?

Question

I am connecting external ADC to STM32L0 Microcontroller using SPI interface . Will it be slower than using internal ADC . External ADC might be faster but does SPI interface acts as a bottelneck.

Or any other way round to use external ADC

Answer 1

The speed of an ADC's conversion depends on how and what you measure:

1. How long does it take to initiate a conversion?

   Some ADCs have an automated mode that repeatedly converts its input. Others need just a bit set, yet others need a whole command sequence.

2. How long does a conversion take?

   There are different conversion algorithms, SAR, flash, you name it. Clocked conversions have a clock, and most clocked ADC have some overhead cycles for sampling etc.

3. How long does it take to fetch the result?

   This depends mainly on the interface. You mention SPI, so its clock rate and the number of bytes to exchange add to this. There are ADCs with a parallel interface.

Therefore, to decide whether this or that ADC is faster, you need to calculate all of these values. You might get a butt feeling after some examplary calculations, though.