Sub-mW Self-Oscillating Mixer with Load-Tolerant VCO Configuration: Evaluation and Design

This paper aims to investigate and propose a solution to the loading effect present in self-oscillating mixer (SOM) topologies. In such topologies the mixer is stacked on top of an LC voltage controlled oscillator (VCO) to achieve ultra-low power (ULP) operation. Thus, the VCO is loaded by the mixer section, and the circuit performance affected. A novel ULP 2.4 GHz SOM designed in standard CMOS 0.13 µm process is proposed in this paper, it based on a load-tolerant LC-VCO configuration where the LC-tank is isolated from the direct coupling to the mixer. The circuit is a stack of a double balanced mixer in switched transconductance configuration and a PMOS LC voltage controlled oscillator (VCO). Post-layout simulations were conducted, showing a conversion gain of 8.12 dB associated with an IIP3 of –12 dBm and a single sideband noise figure of 16 dB. The SOM achieved a phase noise of –114.2 dBc/Hz @ 1 MHz offset, with a tuning range from 2.12 to 2.5 GHz. It consumes an ultra-low power of only 615 µW from 1.2 V supply voltage. The proposed circuit also demonstrated its robustness while subjected to different process-voltage-temperature (PVT) conditions and Monte Carlo simulations.