Gain Adjustment Control for an Active EMI Filter

In this paper several implementations of variable gain amplifiers are investigated, for achieving maximal performance for a feedforward active EMI filter (AEF). Due to the inaccuracy of variable gain or high frequency behavior, all the known implementations do not fulfill the requirements for AEF. Therefore, a new setup with a temperature dependent resistor is investigated. With this setup a high intersection loss of 28 dB at 382 kHz and 20 dB over a frequency range from 150 kHz until 500 kHz is achieved.