Publication: Design of a band gap reference voltage with trimming circuit for performance tuning in CMOS 180nm technology
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Date
2024-07
Authors
Tan, Yun Ling
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Abstract
A bandgap voltage reference (BGR) circuit is used to provide a stable output for analog and digital blocks such as A/D and D/A converters. The output needs to be stable across several aspects, including temperature, power, and process variations. The BGR utilizes two quantities with opposite temperature coefficients (TC): PTAT (Proportional To Absolute Temperature) and CTAT (Complementary To Absolute Temperature). These quantities are added through multiplication with the correct weighting factors to achieve stability. However, process, voltage, and temperature (PVT) variations can affect the overall performance of the BGR. Process variation occurs due to the lithography step, while voltage variation is caused by fluctuations in the power supply. Temperature deviations can cause mismatches and functional failures. Hence, a trimming circuit is required to tune the performance of the BGR due to PVT variations. In this project, a bandgap reference voltage with a trimming circuit is designed. The overall circuit is constructed using 180nm CMOS technology. A stable BGR output of 1.2V is expected from this project. A two-stage operational amplifier with a gain higher than 60dB and a phase margin of 45° is required. The workflow of the project starts with identifying the properties of MOSFETs for ease of circuit calculation. Next, the calculation and design of the bandgap voltage reference and the two-stage operational amplifier are carried out. The trimming circuit is built to maintain the performance of the BGR. Simulations for both components are conducted
to check the performance of the circuit. At the pre-layout simulation, the two-stage OPAMP achieves a DC gain of 75.2611dB and a phase margin of 77.633°. Across all corners of the pre-layout and post-layout simulations, the output reference voltage is 1.2V, with a temperature coefficient lower than 30ppm/°C.