A very compact KHN filter with multidecade tuning

A very compact implementation of a multifunction Kerwin Huelsman Newcomb (KHN) filter that can be frequency tuned almost seven decades, from 0.2 Hz to 1 Mhz, is presented. Tuning is achieved by means of high-value, programmable active resistors biased using the quasi floating gate (QFG) technique and linearisated through capacitive gate voltage averaging. The circuit, realized in a 0.5 mum standard CMOS technology using only four CMOS inverters, six small capacitors, six small resistors and two programmable active resistors, occupies a total area of 0.02 mm², dissipates 3.45 mW and presents a dynamic range at 0.1 % THD of 55.86.