A dual-slope RDC using T-Network for Low Resistance Measurement

A novel resistance to digital converter (RDC) is presented for the measurement of low resistance (Rx, less than 1 $\Omega$). The scheme is based on a dual-slope integrator with a T-network in feedback, three SPDT switches, and a comparator. In a typical dual-slope integrator with low Rx connected to inverting terminal, a large current flows because of which the op-amp behaves abnormally. Even decreasing the input voltage to 0.01 V doesn’t help, because of which till date no RDC is proposed even for less than 100 $\Omega$ measurement. In the proposed scheme, Rx is connected to the middle branch of the T-network, while a fixed resistance and a feedback capacitor are connected to the other two remaining branches. The T-network boosts the input current entering the feedback capacitor thereby increasing the sensitivity which is a novelty. During charging, the lead resistance (RL) connecting Rx is measured, while during discharging, the Rx+$\mathrm{R}_{\mathrm{L}}$ is measured. Finally, RL is subtracted to accurately measure Rx. Hence the scheme is independent of RL in a two-wire type configuration, which is another novelty. The simulation results showed an average error of 0.0241 % in the range of 0.1 $\Omega$ to 0.9 $\Omega$.