Resistor-BJT-less PTAT Current Generator with Single Threshold MOSFET

Abstract

In this article, we present a proportional-to-absolute-temperature (PTAT) current generator that employs only MOSFETs, without the use of resistors or bipolar junction transistors (BJTs). Traditional PTAT current generators are based on the voltage difference between the base-emitter junctions of two BJTs. However, the fabrication of BJTs is increasingly limited in advanced process nodes due to their large area overhead and poor scalability. Conventional MOSFET-only designs, often rely on large resistors or suffer from high line sensitivity and poor linearity due to the channel length modulation effect. The proposed PTAT current generator utilizes two self-cascode structures, each operating in weak and moderate inversion. To enhance line sensitivity, the design incorporates a regulated cascode configuration that suppresses the channel length modulation effect. The sizes of the transistors are determined using the ACM model. In addition, by utilizing only a single type of MOSFET, the design could improve reliability against process variations. Consequently, the proposed design achieves high linearity with an R2 value exceeding 0.9959 and exhibits line sensitivity below 0.25%/V.