Subthreshold current reference suitable for energy harvesting: 20ppm/C and 0.1/V at 140nW

摘要

A new CMOS ultra low power, resistor free, current reference is presented which is composed of two current generators, a current scalar, and a current subtraction circuit. Typical reference topologies generally add two current signals with opposing temperature coefficient (TC) polarities to generate a near zero TC reference current (Ir). The proposed circuit generates two currents (Ia and Ib) with the same polarity TCs that are scaled with differing slopes, and subsequently ratioed and subtracted from each other to form an Ir. In each current generator, the amplifier's built-in offset voltages track thermal voltages (VT) that are forced across resistive MOSFETs, contained in self-cascodes (SC), to make Ia and Ib. The magnitudes of Ia and Ib are adjusted semi independently from their TCs via MOSFET's aspect ratios. Also by setting MOSFET aspect ratios, the current scalar and subtraction circuit deducts the adjusted Ia and Ib from one another to form an Ir optimized for near zero TC. All generated currents are independent of MOSFET's threshold voltage (VTH) and primarily a function of MOSFET's mobility (u) and thermal voltage (VT), thus aiding performance to specifications over changes in temperature and fabrication process variations. Simulations, including montecarlo (MC) and worst case (WC), indicates the following specifications are achievable: current consumption (Idd) ~ 150nA, TC ~ 20 ppm/C, Voltage Coefficient (VC) ~ 0.1 %/V, power supply rejection ratio (PSRR) ~ -65 db, and power-up time (tsu) ~ 14 milliseconds. Preliminary die size is about 101 micro meter (um) per side.