I am working on a project that needs simultaneous ADC/DAC. The specs of the on-board ADC in typical microcontrollers are pretty weak, and separate ADC with good specs are much more expensive than audio codecs. For example, compare these three options:
(A) STM32F373 has three 16-bit, 50ksps max ADCs which reach just under 15 bits effective. This is maybe the best from ST for high resolution ADC; it also has some high-speed 12-bit ADCs and some DACs. Price: $3.26.
(B) an I2S-based audio codec, the PCM3168A has six 24-bit, 96ksps ADCs with 17.5 effective bits (if my reading of the datasheet is correct). This also has eight DACs with similar specs. All inputs/outputs are fully differential, and the highpass filter on the ADC can be turned off. Price: $4.90.
(C) the least expensive TI ADC with similar specs is the ADS1271, a 24-bit, 105ksps ADC with also ~17.5 effective bits. However, this is a $6.31 part, and has only one channel! A four-channel part goes for $14.65.
Thus, using audio codecs for measurement seems rather attractive.
Why not do this? Are there any unexpected drawbacks to using audio codecs for measurement?
Best Answer
Audio codecs are very linear and very low noise, but they are usually AC-coupled to eliminate DC offsets, and their absolute accuracy (scale factor) is not very tightly controlled, since these aspects are not as important in audio work. This makes them less suitable for general ADC/DAC applications.