Design of a High Temperature 2.37 GHz Voltage-Controlled Oscillator With GaN-on-SiC HEMTs

This paper presents a high temperature voltage-controlled oscillator (VCO) for downhole communications. The VCO with the center frequency of 2.37 GHz is prototyped with 0.25μm GaN-on-SiC technology high electron mobility transistors (HEMTs) and microstrip transmission lines on Rogers 4003C PCB. The measured operating temperature of the VCO ranges from 25 °C to 225 °C. A minimum tuning range of 66 MHz and less than 20% variation for the output power of 17 dBm are achieved at 225 °C. The frequency variation remains below 1.5% over the temperature range of 25 °C to 225 °C, and the harmonics power level is 20 dB lower than the fundamental. A phase noise of -131 dBc/Hz at 1 MHz offset frequency is achieved at 225 °C.

I. Introduction

The oil and gas industry’s exploration of deeper wells necessitates electronics operating at temperatures above 210 °C [1], [2]. However, existing electronics for those systems are incapable of prolonged operation at temperatures greater than 150 °C [3]. Cooling and conventional heat extraction techniques are impractical for the application due to added weight, power consumption, and increased complexity. In addition to the thermal limitations, existing systems operate at a low frequency with a correspondingly low data rate of approximately 4 Mb/s [2]. High data rates are required to support high resolution sensors, fast logging speeds, and additional tools available beyond a single wireline cable [3].