Why and How VCO-based ADCs can improve instrumentation applications

After introducing the basic concepts, we will describe the different VCO-based ADC architectures for instrumentation and biomedical applications published in the recent years. Both open loop and closed loop, high order architectures will be analyzed and compared to other standard instrumentation ADCs. The main solutions given to problems associated with VCO-based ADCs in instrumentation, like VCO's phase noise, linearity and sampling metastability will be reviewed. The comparison with other architectures reveals that the FoM of VCO-based ADCs lags that of conventional ΔΣ modulators. Nevertheless the total power consumption, area and performance make them fairly superior when we consider the total efficiency of the instrumentation system, including signal conditioning pre-amplifiers and references.