A polyphase filter based on CMOS inverters

A new idea for generation of quadrature signals on chip is presented. The topology is based on a passive RC polyphase filter, where the resistive parts are made active by using inverters. The active filter combines quadrature generation, isolation, and gain without losing quadrature performance compared to a regular RC polyphase filter. The filter technique is demonstrated in a 10GHz front-end application where a broadband VCO drives an active polyphase filter to generate quadrature LO signals. By avoiding a quadrature VCO and tuned buffers, significant reductions in chip area are possible.