A SiGe BiCMOS D-Band LNA with Gain Boosted by Local Feedback in Common-Emitter Transistors

The performance of silicon amplifiers in D-band is limited by the low gain of transistors operated close to f(max). Cascode stages, yielding higher gain than a single device, are commonly preferred, but the issue is only partially alleviated. Recognizing that the common-emitter (CE) transistor limits the gain of the cascode, this work investigates the use of a local reactive feedback to trade gain for stability. Feedback shifts the CE into a conditionally-stable operating region, and enables a gain beyond its maximum available gain (MAG). Then, when the CE is combined with a common-base, by properly selecting impedance terminations, the resulting cascode displays unconditional stability with superior gain. The concept is exploited in the design of a D-band LNA in BiCMOS 55nm technology which shows 22.8 dB gain, 130-165 GHz operating frequency and NF down to 5 dB with 40mW power consumption. Measured results compare favorably against state of the art.