Single transistor RC-only second-order allpass filters

In this letter, all possible single transistor RC-only second-order allpass filters obtainable from a four impedance common-source topology are reported. It is shown that there are only seven such filters with only one of them being a minimum component canonical 2R-2C filter. Two of the found filters are designed and simulated in a 65-nm CMOS process. © 2019 John Wiley & Sons, Ltd.