0.7-V supply, 21-nW All-MOS voltage reference using a MOS-Only current-driven reference core in digital CMOS

A nano-power all-MOS voltage reference circuit is proposed without any integrated resistor or bipolar transistor to generate multiple voltage sources in inexpensive digital CMOS technologies. The design is based on a current-driven voltage reference core made by standard nMOS transistors only, and can be powered up by a flexible biasing current with no consideration on its temperature characteristics. The sensitive core is shielded from the unregulated voltage supply via a voltage follower MOS transistor, whose gate terminal is driven by a supply-insensitive voltage source coming from the internal biasing configuration. The additional voltage reference is generated using the type of the biasing current made by the main voltage reference loaded by a transistor. A MOS-only implementation of the proposed reference employs MOS devices instead of passive resistors and linear capacitors. A prototype of the proposed solution consumes 30 nA with an area of 0.01 mm(2) in 0.18-mu m CMOS process, producing a main voltage reference of 147 mV while operating at the supply voltage down to 0.7 V. Simulation results demonstrate an average temperature coefficient (TC) of 66.38 ppm/degrees C for a temperature range of -40 to 120 degrees C. The line sensitivity is about 0.031%/V for the line voltages above 1.3 V. The mean power supply rejection ratio (PSRR) is -90 dB and -64.4 dB at 10 Hz and 1 MHz, respectively, when the voltage supply is set to 1.8 V and an equivalent MOS capacitor of 5 pF is used at the output. The 1% start-up settling time is 240 mu s for a 1.0 V voltage supply step, and can be reduced by increasing the supply voltage magnitude.