A LOW-NOISE BASEBAND 5-GHZ DIRECT-COUPLED HBT AMPLIFIER WITH COMMON-BASE ACTIVE INPUT MATCH

This paper reports on an HBT direct-coupled 2-stage amplifier that use s active common-base input matching to provide multi-decade frequency performance from dc to 5 GHz. This work benchmarks the first reported HBT noise results of an HBT amplifier using common-base active input m atching. The 2-stage amplifier consists of a common-base input stage t hat is directly coupled to a Darlington feedback amplifier output stag e. The common-base input can be bias tuned to achieve > 13-dB return l oss at 3 GHz and a minimum noise figure of 2.9 dB at 1 GHz. A gain of 17.5 dB with a 3-dB bandwidth greater than 5 GHz was achieved under lo w-noise input bias. This amplifier topology can be implemented without the use of a complex microstrip process, which typically integrates b ackside vias and microstrip matching components. The compact amplifier consumes an area of 0.82 x 0.47 mm2, which is 10 times smaller than a previously reported 2.5-4 GHz narrow-band passive matched HBT amplifi er with similar noise and gain performance.