Improved Biquad Structures Using Double-Output Transconductance Blocks for Tunable Continuous-Time Filters

A family of g_m-C biquad structures is derived. These biquads require only a pair of grounded capacitors and three transconductors. It is shown that a pair of complex zeros can be realized simply by replicating the output stage of the transconductance block, thereby constructing a second output current that is proportional to the original output current. Although these biquad structures are very compact, they allow independent programming of the filter's center frequency andQ . IC simulations and measurements are presented using a fifth-order tunable filter as an example.