An analytical approach to designing millimeter‐wave LNAs with transformer‐based matching networks

Abstract

In this article, an analytical method for designing transformer matching network of millimeter‐wave (mm‐wave) low noise amplifier (LNA) is presented. In the circuit design, neutralizing capacitors (NCs) structure is used to mitigate the intrinsic gate‐drain feedback capacitance in the transistor for increasing the reverse isolation and available gain, thus allowing the common source (CS) structure can be regarded as an unilateralized active amplification part. The equivalent circuit of the active amplification part and the matching transformer network is modeled, then the analytical matching equations can be established, and the required matching transformer parameter can be determined quickly. As a proof of concept, a Ka‐band LNA operating at 37–43 GHz is designed and implemented in 65 nm complementary metal oxide semiconductor. The measured results show that the small signal gain of the circuit is 19.2–20.5 dB at 37–43 GHz. The noise figure (NF) in the operating band is 3.2–4.2 dB, and the minimum NF is 3.2 dB at 40.2 GHz. The chip area is only 0.08 mm2 excluding pads.