GaAs bipolar wideband oscillators

The aim of this work was an investigation of the GaAs heterojunction bipolar transistor (HBT) for wide tuning range, low phase noise oscillators including, for the first time, a YIG-tuned HBT oscillator. The article describes two types of electronically tuned oscillators, firstly ones based on varactor tuning and secondly a YIG tuned type. Varactor tuned oscillators (VTO) offer high tuning rates and low power consumption in a small, light-weight package. Whilst tuning ranges are adequate for many applications, they are smaller than can be obtained with a YTO. The limited Q of wide capacitance range varactor diodes degrades the phase noise of VTOs. By comparison the YIG-tuned oscillator (YTO) has a very wide tuning range (though not such high tuning rates as a VTO) with good linearity and excellent phase noise performance. This paper will give results on these two types of oscillator and compare them with similar circuits built using GaAs FETs or silicon BJTs