Projeto de um indutor ativo CMOS de baixa potência para circuitos deslocadores de fase operando em sub-GHz

Abstract

In the realm of low-power RF ICs for the UHF band, demands have grown for integrated systems that operate without batteries and consume minimal energy on a single chip, known as SoCs. Inductors play a crucial role in front-end circuits, but their use becomes challenging in sub-GHz frequencies. This is because higher inductance requirements mean they take up more die area and often have lower quality factors. This project aims to design an active inductor that meets the need for higher quality factors and smaller silicon area compared to traditional planar inductors. The goal is to optimize the topology to achieve low power consumption and improve quality factors for phase shifters operating at sub-GHz applications. Initially, a simplified active inductor topology was designed for validation and analysis. Following this, an ultra-low voltage balanced active inductor was developed using inverter-based OTA. However, reducing VDD increases design complexity and process variations, necessitating methods to mitigate these issues through CMFB circuits and sub-circuits for transistor biasing. After developing the active inductor, a 400 MHz phase shifter was implemented using a T-differential network. These circuits was designed in a CMOS 65 nm process. Two versions of the active inductor were implemented: the first with a single-ended output and VDD = 1.2 V, achieving a maximum Q of 14.44 with a power consumption of 1.3 mW, and the second with a differential output and VDD = 0.4 V, achieving a maximum Q of 215.06 with a power consumption of 300.56 μW and a SRF of 1.57 GHz. A strategy for varying the inductance of the active inductor based in a 4-bit selector applied to the phase shifter resulted in a phase shift (∆φ) of -79.91◦ with only 1 section. With 5 sections, a full 360° phase shift can be achieved with power consumption between 1.50 mW and 3.65 mW according the bit selector combinations. Keywords: Active Inductor. Sub-GHz Circuits. Low Power. Phase Shifters.