A Novel Dual-Slope Resistance to Digital Converter With Lead Resistance Compensation

A novel dual-slope resistance to digital converter (RDC) for compensating lead resistance is presented. The RDC uses a dual-slope analog-to-digital converter (ADC) structure along with three switches and a diode. It completes measurement in one charging–discharging cycle only, hence provides an improvement to existing RDCs based on direct microcontroller interfaces (DMIs), where two or three charging–discharging cycles are required. Moreover, it incorporates the feature of lead resistance compensation in dual-slope RDCs. The scheme works by connecting the resistive sensor to the input terminal of the integrator of the dual-slope ADC. In the charging path (or mode), sensor resistance is presented along with a lead resistance; and in discharging path, sensor resistance is bypassed, and only lead resistance is there. The difference between the RC time constant during these two modes is used to find the sensor resistance. The diode is used to turn on a switch for bypassing the resistive sensor. The diode voltage drop is not there in the charging and discharging path, which is another novelty. A detailed error analysis is also carried to evaluate the performance of the scheme considering switch resistance, diode voltage drop, voltage mismatch, and opamp noises. The scheme works with low-value resistive sensors ( $\approx 100~\Omega $ ), a feature not found in the existing dual-slope RDCs. The hardware prototype of the proposed scheme on the breadboard shows a measurement time of 2.09 ms with an average error of ±0.04% at 100 $\Omega $ when lead resistance varied from 20 to 100 $\Omega $ . The scheme takes 23.44% less time for measurement.