The design and characterization of a broadband radio-frequency variable-gain baseband amplifier, enhanced with tunable input-impedance matching and implemented in a 22 nm fully-depleted silicon-on-insulator technology is presented. The proposed amplifier utilizes the back-gate control of the transistors offered in the technology for gain tuning. Using a tunable nFET-based resistor, the amplifier features an adaptive input impedance and can be matched to various circuits, such as a mixer with low to moderate output impedance to serve as a final stage to drive a 50 Ω load. Measurement results show an achieved gain variability of about 9.2 dB with a maximum gain of 13.7 dB. The designed amplifier obtained a 3 dB bandwidth of nearly 20 GHz covering multiple industrial, scientific and medical (ISM) frequency bands. The circuit consumes a power of 5.3 mW from a 1 V power supply. The chip area including pads amounts to 0.277 mm2.