Transducer with Thermal Sigma-Delta Modulator

This paper proposes a simple circuit topology to implement an A/D converter using thermal Sigma-Delta modulator with a thermoresistive sensor. Equations of the converter behavior are presented, and show their use for estimating temperature and thermal radiation. The influence of sensor parameters in the signal to noise ratio of the system are also presented. Simulation and experimental results are showed too. In this A/D converter, the measured variable is directly converted to digital by eliminating the classical stage of signal conditioning which the measurement variable is firstly converted to the electrical domain and then is made an analog to digital conversion. It is also shown that the output binary code has a linear relationship with the measured variable throughout the measuring range. The major contributions of this paper are: the proposal for a thermal A/D converter simplified topology and a theoretical deduction of the static behavior of the converter that relates the sensor parameters and the obtained result with the measured variable. This approach can be useful as a basis for a smart A/D converter design in any temperature or thermal radiation range allowed by the sensor and can be extended for measuring fluid velocity.