A 400nW CMOS bandgap voltage reference

A resistorless 400 nano-Watts bandgap voltage reference in standard 0.25µ digital CMOS process is presented. Parasitic vertical bipolar transistors (BJT) are used to generate a series of cascaded thermal voltages (VT), which is summed with a base-emitter voltage (VBE) to produce a ∼1.25V bandgap voltage (VBG). Statistical contributions of CMOS amplifiers' inherent random noise, offset, and drift terms to the VBG are not multiplied but rather accumulated by the square root of number of additions, fundamentally because the proposed configuration uses summation and not multiplication to generate the bandgap's proportional to absolute temperature (PTAT) term. Such a bandgap can operate at ultra-low currents (i.e. nano-amperes) without using (large size) resistors, which saves significant die area. This design does not require special transistors, and it does not stack parasitic BJTs that could impose VDD headroom constraints. Furthermore, the design does not use multi-staged (special hybrid or) CMOS voltage followers with built-in offset voltage to generate pseudo-PTAT voltage. Therefore, manufacturability and portability across different process nodes at standard CMOS foundries is optimized. Monte Carlo simulations and analysis demonstrates that a temperature coefficient (TC) of about ±50 ppm/°C over a 200°C temperature range can be achievable, and voltage coefficient of about ±0.2% / V with VDD spanning 1.5V to 4.5V can be realized.