8 GHz tunable CMOS quadrature generator using differential active inductors

The design and implementation of a new 8 GHz tunable quadrature generator using a differential active inductor embedded in the local oscillator buffer are presented. The design has a much smaller form factor compared to the sequence asymmetric polyphase filter used as quadrature generator. It relaxes the coupling between the tuning of the output signal amplitude and quadrature phase and facilitates the application of automatic gain and phase control circuitry to compensate for process and temperature variations. It eliminates the need for additional buffering stages at the output of the quadrature generator and results in a considerable reduction in power consumption. A prototype implemented in 0.18 μm CMOS technology, operating from a 1 V power supply and consuming 12 mW of power, features a measured gain of -2 dB and a worst case phase and amplitude mismatch of better than 1.5° and 1 dB respectively over a bandwidth of 100 MHz at 8 GHz. The design meets the potential specifications of 4G OFDM direct conversion receivers.