A resistorless switched bandgap voltage reference with offset cancellation

This work presents a novel Switched-capacitor Bandgap Voltage Reference (SCBGR) circuit that dispenses entirely the use of resistors. The vEB negative drift and the thermal voltage (VT) positive drift voltages are both generated by the same PNP vertical bipolar transistor, avoiding diode mismatch problems. The current sources that are used to generate different junction current densities are averaged in the switching process, reducing their mismatch impact on the circuit performance. A switched-capacitor circuit stores and processes these voltages, generating the bandgap reference voltage after 5 clock cycles. Since capacitors are used instead of resistors, variability problems like average process spread and device mismatches are reduced. The proposed topology was designed and simulated in CMOS for 180 nm process. This paper presents a systematic comparison to the traditional dual-BJT BGR and demonstrates the better performance of this new topology with respect to the former. Monte Carlo simulation shows significantly lower spread resulting from variations in the output reference voltage and in its temperature coefficient (TC).