A 28 GHz balun-first LNA with db-linear 32 db gain range for 5 G applications

This letter presents a 28 GHz balun-first low noise amplifier (LNA) featuring a wide dB-linear variable gain range. The architecture of LNA includes three-stage cascode amplifiers. An integrated balun at the input stage provides RF ESD protection and converts a single-ended signal to a differential one (S-to-D). A transformer-based dual-resonant matching network is designed and analyzed to achieve wideband performance. To realize a continuous dB-linear variable gain range and consistent input/output matching, gain control is implemented in the second stage using a 5-bit digital-to-analog converter (DAC) for a 32 dB gain range. The DAC can generate a nonlinear analog voltage to control the gate of the common-gate transistor in the second cascode stage, inversely compensating for the nonlinear gain variations of the cascode amplifier. The LNA is fabricated in 65-nm CMOS process with a core size of 0.154 mm². Measurement results exhibit a maximum gain of 33.5 dB and a minimum noise figure (NF) of 3.65 dB with a 3-dB bandwidth of 23–29.5 GHz. The measured variable gain range is approximately 32 dB across 32 different gain states, with a linear gain step of ~1 dB per state and an IP1dB ranging from −6.5 dBm to −35.25 dBm. The power consumption is 35.4–48 mW from a 1.2 V supply voltage.