A high‐isolation linear folded mixer for ISM band in UMC 180NM CMOS technology

Abstract

This paper presents an integrated radio frequency (RF) downconversion folded mixer that operates in the 2.4 GHz industrial, scientific, and medical (ISM) band by using UMC 180 nm RF CMOS. It is implemented by using a double-balanced transconductance switch (GmSw) configuration. The proposed mixer converts the incoming signal to a small signal RF current followed by a PMOS current mirror structure. The circuit can operate with a power supply of less than 1.8 V. A superior isolation is achieved by incorporating a novel folded structure with a CMOS local oscillator (LO) stage. The proposed folded mixer achieves 7 dB of conversion gain and 8.5 dBm of the third order input intermodulation product. The highest measured isolation between the LO-IF, RF-IF, and LO-RF ports is 50, 45, and 65 dB, respectively.ABSTRACT: A novel common mode suppression network (CMSN) for balanced structures is presented. The structure is a symmetrical transmission line loaded with k g /4 stubs, where k g is the guided wave length at the frequencies to be suppressed. The CMSN is a circuit that can be independently designed to improve the common mode (CM) behavior of the attached circuits without degrading their differential mode (DM) performance. As an example, a balanced bandpass filter (BBPF) with an undesired 0dB CM peak is improved in more than 30 dB, whilst the DM bandpass is barely affected.