Advantages and Disadvantages of Analogue Multiplexer vs a ADC chip. For having more analogue inputs on micro-controller. Thx
Sometimes you really need to simultaneously sample several inputs at the same time and a separate ADC for each channel is typically used. For example, the TI ADS1274/1278 has 4 or 8 channels of decent ADC.
If your ADC (on chip or otherwise) is fast enough to sample all the channels in turn then you can perhaps save money and power by time-sharing it between the channels.
Speed is going to be your limiting factor if using a Multiplexer. Multi input ADCs and uCs have only a couple actual AtoD converter and an internal multiplexer to feed them. The designers of these systems have taken care of all the timing constraints of switching channels and sampling.
If your using your own Multiplexer then you will have to take care of the timing. If speed is not a concern then a then either solution is fine. If speed is a concern then the multi input ADC is your only choice.