High temperature low noise SOI-CMOS preamplifier for wireless telemetry system
Date of Issue2015
School of Electrical and Electronic Engineering
High temperature electronics find many applications such as down-hole drilling, aerospace, automotive and nuclear. Elevated temperatures are required for these applications to operate reliably. Electronics for drilling application explore oil wells by sensing, logging and processing data like temperature, inclination, heading and pressure of the strata. Data acquisition system’s biggest challenge for down-hole-drilling application is the very high operating temperature, which may be up to 200 °C under more than 2 km of the earth’s surface. At high temperature, bulk-CMOS transistors exhibit many drawbacks: increase in junction leakage, shift of threshold voltages, and reduction of mobility. Among these drawbacks, the most serious problem is the excess junction leakage current at high temperature. Circuit performance is reduced due to the loss of charges at dynamic node or the loss of bias current or more seriously, the latch-up. A proper technology choice is a first consideration for successful operation of integrated circuits in such high temperature regime. By getting rid of the reverse-biased diodes between substrate/well and the source/drain region, Silicon-on-insulator (SOI) technology significantly reduces the leakage current while keeping most of the desirable properties of bulk CMOS technology. Wireless telemetry system for Measurement While Drilling operations, which is also known as Logging While Drilling, is an effective way to improve drilling operations’ efficiency. The front end amplifier is the most critical component of the receiver in a wireless telemetry system. The noise performance of the front-end amplifier determines the detection accuracy of the overall system. Front-end amplifiers used in down-hole-drilling wireless telemetry system at low frequencies is a main challenge due to the flicker noise of the MOS transistors. Power efficient high temperature capable preamplifiers with low input noise are required. In this thesis, two high temperature low-noise 1-µm partially depleted (PD) SOI CMOS preamplifiers for wireless telemetry system are presented. These designs are targeted for operation at up to 200°C. To achieve low flicker noise, PMOS devices, operating in moderate inversion, are used for the differential input of the preamplifier. MOS devices in the deep triode region are used for resistive source degeneration to reduce flicker noise and the effective transconductance of NMOS devices. Simulation shows that the input-referred noise of the preamplifier is 83 nV/sqrt(Hz) at 800 Hz. The chopper technique is chosen mainly for its very low noise performance at low frequency. For the three opamp chopper amplifier, simulation shows that the output-referred noise is 25.6 nV/sqrt(Hz) at 800 Hz. The purpose of these designs is to investigate low noise performance of the front end amplifiers under high-temperature condition. Both the circuits are fabricated using XFAB SOI 1-µm process. Experiments prove that the preamplifier can work properly at the temperature 180 °C with a gain of 17.65 dB at 20 kHz and the chopper amplifier can work properly at 225°C with a gain of 19.65 dB at 20 kHz.
DRNTU::Engineering::Electrical and electronic engineering::Integrated circuits