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Digital lock-in amplifier for precision audio frequency bridge

This paper introduces a custom digital lock-in amplifier for detecting the imbalance signal of a precision audio frequency bridge. The lock-in amplifier is designed with a PXI measurement system which is equipped with a signal generator and simultaneous data acquisition adapters. The advantage of this design is that the demodulation algorithm can be flexibly reconfigured when the imbalance signal changes in the AC bridge system. The resolution and linearity of the lock-in amplifier can also be improved by using higher resolution A/D adapters. Simulations and experiments have verified the basic concept of the designed lock-in amplifier.