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

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 15.1 dBm and the noise figure is 9.3 dB at maximum gain. The corresponding input IP3 is 15.1 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.<
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