A polyphase filter based on CMOS inverters

Research output: Contribution to journalArticle


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 10 GHz front-end application where a broadband VCO, having a tuning range of 1.44 GHz, drives an active polyphase filter to generate quadrature LO signals. According to simulations the quadrature phase error shows a typical tuned behavior and stays below 0.8 degrees for the complete tuning range. Since the signal amplitude is high throughout the filter the noise is low, below 160 dBc/Hz at 10 MHz offset. The high amplitude also reduces the need for high gain tuned buffers, thereby enabling significant reductions in chip area.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Electrical Engineering, Electronic Engineering, Information Engineering


  • quadrature generation, CMOS, polyphase filter
Original languageEnglish
Pages (from-to)7-12
JournalAnalog Integrated Circuits and Signal Processing
Issue number1
Publication statusPublished - 2007
Publication categoryResearch