Self-balancing DC bridge circuits using resistive mirror based voltage controlled resistors

Two types of self-balancing DC 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 bridges are automatically balanced with the output voltage directly proportional to the measured resistance. The behaviours of the proposed circuits have been verified by experiment. The maximal relative error of the proposed SBDCB circuit is less than 0.05% in the measured resistance range from 0.3 k/spl Omega/ to 300 k/spl Omega/.