A new family of active variable equalizers

An active version of the Bode-type variable equalizer has been designed. Variable equalizers are widely used for amplitude equalization in wide-band transmission systems because they possess the unique property that the equalization shape does not change as the amount of equalization is varied. Such a property is especially desirable when equalizing cable of varying length. The active variable equalizer to be described here overcomes many of the disadvantages associated with the conventional passive version, which include the need for inductors, a complex design procedure, and incompatibility with modem electronic control elements. This design also has advantages over other active variable equalizer designs. Such an equalizer is especially applicable to precision equalization at frequencies below 10 MHz. As an example, a
\sqrt{f}
equalizer can be built with a
\pm 9-dB
range having only
\pm 0.05-dB
maximum error. The equalizer is easily built with operational amplifiers and
RC
networks.