Improved Biquad Structures Using Double-Output Transconductance Blocks for Tunable Continuous-Time Filters
NOTE: At the time of publication, the author Vladimir Prodanov was not yet affiliated with Cal Poly.
A family of gm −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.
Vladimir I. Prodanov and Micheal M. Green. "Improved Biquad Structures Using Double-Output Transconductance Blocks for Tunable Continuous-Time Filters" International Journal of Analog Integrated Circuits and Signal Processing 13.3 (1997): 233-240.
Available at: http://works.bepress.com/vprodano/8