Bandwidth Enhancement of a Current Sensing Trace by Adaptive Inverse Filtering

In our previous article we proposed a novel current measurement technique, the CSRTRI (Current Sensing by Real-Time Resistance Identification), which is characterized by the main principle of the in-situ identification of the current rail's resistance by an auxiliary inductive coil in the face of continuously varying conductor-temperature. The feasibility of the method was shown, and an accuracy of 0.93%...1.10% was demonstrated. The accuracy is limited by the stray inductance of the Cu-trace, which in combination with the resistance forms a temperature dependent highpass filter. We introduced an analog RC-lowpass filter based compensation method at 25°C nominal temperature and reached a bandwidth of 2 MHz. In this paper, we present an adaptive digital inverse filtering based compensation method instead. The advantage of this approach is that it covers the whole temperature range of the sensor, not just a narrow nominal value. The enhancement does not require any additional temperature sensor; we will utilize the instantaneous estimate of the copper trace’s resistance from the CSRTRI-algorithm directly to identify the cutoff frequency of the parasitic highpass filter in situ, without the need to determine the copper temperature itself. A temperature dependent time-varying first order lowpass filter of approximately 48 kHz cutoff frequency is applied to eliminate the main inductive overshoots. By this software-based transfer function enhancement a 1.5 MHz overall system bandwidth has been achieved between 20°C and 50°C conductor-temperature.