A Precision Wideband Quadrature Generation Technique With Feedback Control for Millimeter-Wave Communication Systems

An integrated two-stage polyphase filter (PPF) with feedback control for quadrature local oscillator generation at millimeter-wave frequencies is described. To minimize the in-phase (I) and quadrature (Q) mismatch, the second stage of the PPF utilizes triode-region nMOS transistors to implement variable resistors where the resistance is precisely controlled by modulating the shared gate-to-source bias voltage at the gate of nMOS devices. The gate bias voltage of the triode-region devices is set by a feedback loop which changes with variations in process, voltage, and temperature. A prototype quadrature signal generator, employing this PPF design, is integrated in a 28-nm LP CMOS process. A worst case measured phase/amplitude imbalance of 2°/0.32 dB (typical-typical corner dies) and 2.2°/0.55 dB (slow-slow corner dies) is reported over 7-GHz bandwidth for a fixed control current (ICtrl). By retuning ICtrl at every 7 GHz, this IQ generator would maintain the measured quadrature accuracy from 55 to 70 GHz. The core area occupied by the IQ generator circuitry is 20 μm × 40 μm and the device consumes less than 192 μW, of which 120/72 μW comes from the feedback control-loop/opamp, respectively. The proposed PPF method has a simulated input impedance of 150 Ω in-parallel with 18 fF.