Better ADC resolution can be accomplished by oversampling two or more ADC readings and then averaging them. If you’re not satisfied with a microcontroller’s 10 bit ADC and need more resolution, check out this application note from Atmel.
Increasing the ADC resolution by one bit requires 4 ADC measurements. Four 10 bit readings are needed for one 11 bit reading. Similarly, the maximum bandwidth is reduced. If you go from 10 bit to 16 bit, the maximum bandwidth comes to 7600 Hz divided by 46 (i.e, 4096) – that’s only ~2 Hz.