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^o and 0.32dB across a frequency range of 55-70GHz is reported. The core IQ generator size is 20μ m × 40μ m while consuming 81 μW, which includes 9μW for the feedback control loop and 40A from 1.8V supply for the opamp. The input impedance is simulated to be 150Q in parallel with 18fF.