Sigma-delta versus oscillator-based converters in low-cost accurate sensor systems

Indirect Analog-to-Digital (A/D) converters have proven to be very suitable for use in sensor systems. Two different types of indirect converters can be distinguished: synchronous converters (such as Delta-Sigma converters) and asynchronous converters (such as converters based on free-running oscillators). This paper discusses the differences between both types for the use in low-cost sensor systems. It is concluded that the converter which is based on an asynchronous modulator is for some aspects superior to a Delta-Sigma converter and can be regarded as the optimal converter for use in low-cost sensor systems