Analysis and Optimization of Voltage-Driven Double-Balanced Passive Mixer for MICS Band Receiver

Abstract

This paper presents analysis of a 25% duty-cycle fully-differential double-balanced passive mixer dedicated to medical implantable devices. The proposed passive mixer is part of a medical implant communication service (MICS) receiver front-end operating at 402–405[Formula: see text]MHz. By performing time-domain analysis, two LTI models have been developed to study the fully-differential double-balanced passive mixer: A simplified model and a complete model taking into account harmonic components. Both models account for the AC coupling capacitors at the mixer input and account for baseband voltage variation over one LO period. In this study it has been shown the ability of mixer input impedance matching by varying baseband resistor at the mixer output. The frequency of match can be controlled by varying the AC coupling capacitors and baseband capacitors. The performance of the proposed models was compared with that of the mixer and the results were very close. In particular, the results of simulations of the input impedance as a function of the baseband resistance and as a function of the IF frequency show the validity of the proposed models. The main parameters of the passive mixer such as input impedance, gain and noise figure (NF) were optimized taking into account the constraints of our application. The proposed mixer is designed to operate at LO frequency of 403.2[Formula: see text]MHz. Transistors size is optimized to meet the receiver specifications. The mixer realizes a conversion gain of 0[Formula: see text]dB and an NF of 4.8[Formula: see text]dB. Linearity simulations show 25.2[Formula: see text]dBm for IIP3 and 9.66[Formula: see text]dBm for [Formula: see text]dB. The mixer consumes 1.44[Formula: see text]pW without LO circuit.