A low supply voltage 2µW half bandgap reference in standard sub-µ CMOS

Design of a sub-1V supply, half bandgap voltage reference (V_r) is proposed, which can generate V_r of about 620mV and operate with power supply voltage (V_DD) as low as about 750mV at 0°C. To enhance manufacturability and facilitate ease of design portability across different process nodes, the design is implemented in standard 180nm digital CMOS without the need for any special CMOS processes or non-conventional devices. The proposed topology only utilizes parasitic substrate bipolar junction transistors (BJT), poly resistors, and normally configured CMOS transistors that chiefly operate in subthreshold. Lower V_DD is achieved by segregating BJTs from the resistors used in the proportional to absolute temperature (PTAT) and the complementary to absolute temperature (CTAT) signal loops. Such configuration results in lowering the emitter-base voltage (V_EB) via biasing the BJTs at n-times (i.e. 100s of times) lower currents than the PTAT and CTAT resistors and signal loops. Therefore, the scarce V_DD headroom in sub-1V applications is freed-up in the PTAT loop from V_EB by V_T × ln (n), or in the range of typically 10%-15% of V_DD. Moreover, biasing the BJT loop at nano-ampere currents keeps the power consumption low, while it avoids using prohibitively large PTAT or CTAT resistors.