A 1.4-dB-NF variable-gain LNA with continuous control for 2-GHz-band mobile phones using InGaP emitter HBTs

We designed a continuously variable-gain low-noise-amplifier (VG-LNA) circuit with a noise figure (NF) of 1.4 dB. This VG-LNA has a diode-loaded emitter follower and a variable-current source. The diode-loaded emitter follower enables gain control without NF degradation at the maximum gain; the variable-current source improves the linearity and widens the range of gain control. It was fabricated by using InGaP-emitter hetero bipolar transistors (HBTs) and has an NF of 1.4 dB at maximum gain, 1.95 GHz, and a 3-V supply voltage. Its maximum gain is 15 dB, its input 3rd-order-intercept-point (IIP3) at the maximum gain is 3.4 dBm, and the gain-control range is 40 dB. The obtained of NF of 1.4 dB is the lowest so far reported for a continuously controlled VG-LNA.