Design of a Lock-in Amplifier with Current-Mode Oscillator

The lock-in amplifier can be used in instrumentation systems as a part of the conditioning circuit that optimizes and supports the signals coming from sensors, being capable of measuring the electrical impedance (or admittance) of such sensors, by exciting them with a local oscillator. In industrial environments and research laboratories, it is important to ensure that the level of current passing through the sensor, usually called Device Under Test (DUT), does not exceed the tolerance and safety limits: 10 mA to 30 mA. In this paper, we proposed the design of a lock-in amplifier with a current-mode oscillator to ensure that the current level is below the tolerance limits. A current-mode Wien oscillator was used based on Current Conveyors, a current-mode building block. Through simulations and experimental measurements, we could check the operation of the designed circuit, pointing out some comparisons with the traditional lockin amplifier with voltage-mode oscillator.