An Efficient Digitizer for Self-Heating Compensation in Resistive Sensor

Self-heating (S-H) error is found in all resistive sensors (R
X
) when interfaced with an electronic circuit for the output signal. This work presents an efficient digitizer circuit for interfacing the resistive sensor to compensate the S-H error. The digitizer utilizes a dual-slope integrator and a comparator to generate a time sequence output signal, which can be directly fed to the digital pin of a microcontroller for signal processing. To minimize the self-heating error, the input current through R
X
is kept small in the micro-ampere range. However, a T-network is connected to the integrating capacitor to boost the incoming current in the feedback path and helps in achieving high accuracy, sensitivity, and resolution. This is a novel feature that has not been reported before. The digitizer is simulated for measuring R
X
in a wide range of 3.63 kΩ to 488.2 kΩ, with corresponding power dissipation of 0.275 mW to 2.03 μW respectively. The current through R
X
ranges from 275.2 μA -2.04 μA, and the measurement time varies from 4.78 ms to 389.3 ms. If this range of current is fed to a conventional digitizer for integrating the feedback capacitor, the circuit requires a longer measurement time (103.4 ms to 13.76 s). However, with the current boosting approach employed (ranging from 21.07-49.41 times) in this digitizer, the measurement time is reduced. It is to be noted that the conventional digitizer with a measurement time of 4.78 ms to 389.3 ms would require 5800 μA – 101.19 μA to pass through R
X
which would dissipate 122.11 mW – 4998.88 μW . Thus, this scheme decreases power dissipation by 444 – 2462.4 times which represents a significant improvement. The proposed digitizer produces accurate results with an average error of ± 0.28 %.