A 55-70GHz two-stage tunable polyphase filter with feedback control for quadrature generation with <2° and <0.32dB phase/amplitude imbalance in 28nm CMOS process.

An integrated two-stage polyphase filters (PPFs) with feedback control is proposed for local oscillator (LO) quadrature generation at millimeter-wave band frequencies. The PPFs second stage utilizes triode-region NMOS transistors to implement variable resistors which are accurately controlled to minimize any IQ mismatch. A prototype quadrature signal generator for use in a homodyne 60GHz receiver is integrated in 28nm LP CMOS process. A worst-case measured phase and amplitude imbalance of 2 degrees and 0.32dB across a frequency range of 55-70GHz is reported. The core IQ generator size is 20 mu m x 40 mu m while consuming 81 mu W, which includes 9 mu W for the feedback control loop and 40 mu A from 1.8V supply for the opamp. The input impedance is simulated to be 150 Omega in parallel with 18fF.