HF-VHF-UHF IQ mixer with a single SPDT switch

Abstract

An I Q mixer topology using passive components and a single SPDT switch is described with simulations and measurements at 7 MHz and 144 MHz. A test fixture permits experiments with a variety of switch candidates. Results are presented for MOSFET switches and an SPDT switch using a hybrid coil and ring of Schottky diodes. SSB conversion loss is near 6 dB. Measured IIP3 is +16 dBm for a MOSFET switch and +6 dBm for the diodes. The Schottky version exhibits much better 2nd order performance and stability of amplitude and phase differences between I and Q ports. Results at VHF using surface mount components suggest that the Schottky diode/hybrid coil switch is a promising candidate for low power near-zero IF applications.