A novel baseband-1.5 GHz monolithic HBT variable gain amplifier with PIN diode gain control

Abstract

This paper reports on a GaAs HBT Variable Gain Amplifier (VGA) which monolithically integrates a GaAs PIN diode as a variable resistor to achieve wide gain control. The PIN diode is made from the intrinsic MBE layers of the HBT collector-base junction which consists of a 7000 /spl Aring/ thick i-region. The novel VGA topology employs active feedback and output buffering to obtain high IP3 performance and is the first PIN-HBT VGA reported of its kind. The VGA obtains 10 dB gain and over 25 dB of gain control range at 1 GHz. The output IP3 is +5.1 dBm and the noise figure is 9.3 dB at maximum gain. The corresponding input IP3 is +5.1 dBm and remains constant over gain control which is an attractive feature of the HBT-PIN VGA. The PIN diode VGA design is realized in a miniature 0.8/spl times/0.4 mm/sup 2/ area. Integrated with a previously developed HBT LNA, the resultant low noise VGA MMIC demonstrates 2.1 dB noise figure, >35 dB gain, +13.5 dBm OIP3, and over 25 dB of gain control at 1 GHz. >