Design of electromagnetically coupled isolation operational amplifiers without input buffer

The paper describes an approach to design of isolation operational amplifiers with electromagnetic coupling. The amplifier includes an RL-multivibrator with nonlinear transformer, a duty-cycle detector and an output amplifier. The multivibrator is used as a DC current sensor. The input DC signals and the feedback signal are applied to the transformer secondaries which results in the magnetic field modifying the core saturation. The multivibrator duty cycle changes. Then the duty cycle detector output voltage changes. The output amplifier further amplifies detector output signal and provides the necessary loop gain