A High-Temperature Folded-Cascode Operational Transconductance Amplifier in 0.8-μm BCD-on-SOI

Abstract

The rapid growth of the hybrid electric vehicles (HEVs) has been driving the demand of high temperature automotive electronics target for the engine compartment, power train, and brakes where the ambient temperature normally exceeds 150°C. An operational transconductance amplifier (OTA) is an essential building block of various analog circuits such as data converters, instrumentation systems, linear regulators, etc. This work presents a high temperature folded cascode operational transconductance amplifier designed and fabricated in a commercially available 0.8-μm BCD-on-SOI process. SOI processes offer several orders of magnitude smaller junction leakage current than bulk-CMOS processes at temperatures beyond 150°C. This amplifier is designed for a high temperature linear voltage regulator; the higher open-loop gain of this amplifier will enhance the overall performance of a linear regulator. In addition, the lower current consumption of the OTA is critical for improving the current efficiency of the linear regulator and reducing the power dissipation at elevated temperature. A PMOS input pair folded cascode OTA topology had been selected in this work, PMOS input pair offers wider ICMR (input common-mode range) and empirically lower flicker noise compared to its NMOS counterpart. By cascoding current mirror load at the output node, the folded cascode OTA obtains higher voltage gain than the symmetrical OTA topology. The PSRR (power supply rejection ratio) is also improved. A on-chip temperature stable current reference is employed to bias the amplifier. The amplifier consumes less than 65μA bias current at 175°C. The core layout area of the amplifier is 0.16mm2 (400 μm × 400 μm).