A 22-to-37.8-GHz Low-Gain-Phase-Error Variable-Gain Amplifier With Impedance-Compensation Technique in 65-nm CMOS Process

This letter presents a wideband variable-gain amplifier (VGA) with an impedance-compensation technique for 5G new radio. To minimize the gain and phase errors of a millimeter-wave VGA in a wide frequency band, a parasitic-capacitance-compensation method based on varactors is proposed to alleviate the input impedance variation of a cross-coupled structure. To extend gain bandwidth and save chip area, compact transformers with various coupling coefficients are employed to design the input, interstage, and output impedance-matching networks. The VGA is demonstrated by using a 65-nm CMOS process. According to the measurement results, the circuit achieves a peak gain of 12 dB with a 3-dB gain bandwidth of 15.8 GHz. Its fractional bandwidth is up to 52.8%. The tested root-mean-square phase and gain errors of the proposed VGA are lower than 1.2 $^{\circ}$ and 0.1 dB across 24–38 GHz, respectively.