GaAs HBT 0.75-5 GHz multifunctional microwave-analog variable gain amplifier

The authors report on a GaAs HBT three-stage variable gain amplifier operating over a 0.75-5 GHz frequency band. The amplifier is broken up into a single-ended HBT LNA pre-amp, an analog current steering differential cascode cell for variable gain control, and a differential amplifier output stage. The pre-amp is required to reduce the inherently noisy differential cascode stage, and an output differential amplifier is used for drive capability and differential to single-ended conversion. The VGA has a maximum gain of 23.8 dB, an IP3 >18 dBm, and a noise figure of 6.5 dB. The variable gain control range is >35 dB. This chip demonstrates the versatility of HBT IC technology which can integrate digital, analog, and microwave circuit functions to achieve high performance in a single monolithic chip.<>