70-90-GHz self-tuned polyphase filter for wideband I/Q LO generation in a 55-nm BiCMOS transmitter

A low-power quadrature local oscillator (LO) generation scheme embedded in a direct-conversion E-band transmitter (TX) is presented. A single-stage polyphase filter is closed in a loop and continuously tuned by means of a quadrature phase detector to maintain precise I/Q signals independently from LO frequency and component variations, thus making the solution wideband and robust against process, supply, and temperature variations. The analog phase detector, realized with fully balanced analog multipliers, is critical to reach high accuracy. Careful circuit analysis and simple design solutions are proposed to avoid systematic phase errors and to maintain high detector gain despite the high operating frequency. The TX, realized in BiCMOS 55-nm technology, delivers a maximum linear output power of 20.5 dBm at 80 GHz with 14% power efficiency. The LO buffers consumes 115 mW from 2.3-V supply while the LO calibration circuits need 16 mW only and allows to maintain a remarkable image rejection ratio of 40 dB or better over 70-90 GHz.