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 and Q. IC simulations and measurements are presented using a fifth-order tunable filter as an example.
continuous-time filters tunable filters active filters biquadratic filters analog integrated circuits