A 1.1- / 0.9-nA Temperature-Independent 213- / 565-ppm/$^\circ$C Self-Biased CMOS-Only Current Reference in 65-nm Bulk and 22-nm FDSOI

TL;DR

This paper presents a highly area-efficient, temperature-independent nA-range current reference using a self-cascode MOSFET, achieving low power consumption and minimal silicon area in 65-nm and 22-nm processes.

Contribution

It introduces a novel CMOS-only current reference based on a self-cascode MOSFET biased by a PTAT voltage, significantly reducing silicon area compared to existing solutions.

Findings

Achieves 213 ppm/°C temperature coefficient in 65-nm process.

Consumes around 5.4-5.8 nW power at sub-1 nA current.

Occupies at least 25× less area than state-of-the-art references.

Abstract

In many applications, the ability of current references to cope with process, voltage, and temperature (PVT) variations is critical to maintaining system-level performance. However, temperature-independent current references operating in the nA range are rarely area-efficient due to the use of large resistors which occupy a significant silicon area at this current level. In this article, we introduce a nA-range constant-with-temperature (CWT) current reference relying on a self-cascode MOSFET (SCM), biased by a proportional-to-absolute-temperature (PTAT) voltage with a CWT offset. On the one hand, the proposed reference has been simulated post-layout in 65-nm bulk. This design consumes 5.4 nW at 0.7 V and achieves a 1.1-nA current with a line sensitivity (LS) of 0.69 %/V and a temperature coefficient (TC) of 213 ppm/$^\circ$C. On the other hand, the proposed reference has been simulated and fabricated in 22-nm fully depleted silicon-on-insulator (FDSOI). This second design requires additional features to mitigate the impact of parasitic diode leakage at high temperature. In measurement, it consumes 5.8 nW at 0.9 V and achieves a 0.9-nA current with a 0.39-%/V LS and a 565-ppm/$^\circ$C TC. As a result of using an SCM, the proposed references occupy a silicon area of 0.0021 mm$^2$ in 65 nm (respectively, 0.0132 mm$^2$ in 22 nm) at least 25$\times$ (respectively, 4$\times$) smaller than state-of-the-art CWT references operating in the same current range.