Emulation of Fractional-Order Impedance with α = 0.5 Using MOSFET Revised RC-Ladder Topology

Approximations of fractional-order capacitors are widely implemented using passive RC ladder topologies. One alternative to this approach is to replace resistors in these topologies with MOSFET devices biased to operate as resistors. To validate this approach, fractional-order capacitors with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</tex> = 0.5 are approximated (with a ±1° phase error target) with MOSFET revised ladder topologies in parallel and series configurations. The measured phases of these realized approximations had average differences of 0.7° and 3.1° for the parallel and series cases, respectively, with maximum differences of 1.7° and 13.3° for the frequency band from 100 Hz to 10 kHz.