A quadrature down converter for direct conversion receivers with high 2nd and 3rd order intercept points

Abstract

This paper describes an I and Q down converter designed for a 800 MHz direct conversion receiver. The down converter employs a bipolar Gilbert cell mixer with degenerated common base input stage that achieves greater than +62 dBm 2nd order input intercept point (IIP2) and +6 dBm 3rd order input intercept point (IIP3) with 4.6 mA at 2.5 Volt. The use of a fully balanced, fully differential topology and divide-by-two quadrature generator has improved the LO to RF signal isolation to better than 85 dB.