A nA-Range Area-Efficient Sub-100-ppm/°C Peaking Current Reference Using Forward Body Biasing in 0.11-$μ$m Bulk and 22-nm FD-SOI

Abstract: In recent years, the development of the Internet of Things (IoT) has prompted the search for nA-range current references that are simultaneously constrained to a small area and robust to process, voltage and temperature variations. Yet, such references have remained elusive, as existing architectures fail to reach a low temperature coefficient (TC) while minimizing silicon area. In this work, we propose a nA-range constant-with-temperature (CWT) peaking current reference, in which a resistor is biased by the threshold voltage difference between two transistors in weak inversion. This bias voltage is lower than in conventional architectures to cut down the silicon area occupied by the resistor and is obtained by forward body biasing one of the two transistors with an ultra-low-power voltage reference so as to reduce its threshold voltage. In addition, the proposed reference includes a circuit to suppress the leakage of parasitic diodes at high temperature, and two simple trimming mechanisms for the reference current and its TC. As the proposed design relies on the body effect, it has been validated in both 0.11-$\mu$m bulk and 22-nm fully-depleted silicon-on-insulator, to demonstrate feasibility across different technology types. In post-layout simulation, the 0.11-$\mu$m design generates a 5-nA current with a 65-ppm/{\deg}C TC and a 2.84-%/V line sensitivity (LS), while in measurement, the 22-nm design achieves a 1.5-nA current with an 89-ppm/{\deg}C TC and a 0.51-%/V LS. As a result of the low resistor bias voltage, the proposed references occupy a silicon area of 0.00954 mm$^2$ in 0.11 $\mu$m (resp. 0.00214 mm$^2$ in 22 nm) at least 1.8$\times$ (resp. 8.2$\times$) smaller than fabricated nA-range CWT references, but with a TC improved by 6.1$\times$ (resp. 4.4$\times$).