Self-balancing linear bridge circuits with resistive mirrors for resistance measurement

Two types of self-balancing direct current bridge (SBDCB) circuits using resistive mirror-based voltage-controlled resistors (RMBVCRs) instead of the classical electromechanical trimming resistors have been designed. The proposed SBDCBs are the first designs reported in the literature that employ the semiconductor-controlled resistors. These bridge circuits have constant currents in their resistive branches. One of the SBDCBs has the variable supply voltage, whereas the other has the constant supply voltage. The resistive original and its mirror image within the RMBVCR have been realized using bipolar junction transistors (BJTs), The bridges are automatically balanced with the output voltage directly proportional to the measured resistance. The conclusions derived by the error analysis have been verified by the experimental results. The maximal relative error of the proposed SBDCB circuit is less than 0.05% in the measured resistance range from 0.3 k Omega to 300 k Omega.