A 5.2-GHz GaInP/GaAs HBT double-quadrature downconverter with polyphase filters for 40-dB image rejection

A 5.2-GHz 11-dB gain, IP/sub 1 dB/=-17 dBm and IIP/sub 3/=-10 dBm double-quadrature Gilbert downconversion mixer with polyphase filters is demonstrated by using GaInP/GaAs heterojunction bipolar transistor (HBT) technology. The image rejection ratio is better than 40 dB when LO=5.17 GHz and intermediate frequency (IF) is in the range of 15 MHz to 40 MHz. The Gilbert downconverter has four-stage RC-CR IF polyphase filters for image rejection. Polyphase filters are also used to generate local (LO) and radio frequency (RF) quadrature signals around 5 GHz in the double-quadrature downconverter because GaAs has accurate thin film resistors and the low parasitic semi-insulating substrate.