Active-RC variable equalizers with minimum number of operational amplifiers

This paper describes some new active equalizers that are based on the Bode principle, but using shaping transfer functions instead of shaping immittances. It is shown that bump equalizers may be realized by circuits containing only one operational amplifier and only one variable element, with sensitivities somewhat higher than previous two-OA approaches. A low-sensitivity configuration using two operational amplifiers (OA\´s) is also considered, which is capable of realizing bump heights in excess of 20 dB and \´s higher than 20 reliably, since it does not use positive feedback or cancelling feedforward.