An electronic device may include wireless circuitry with a baseband processor, a transceiver circuit, a front-end module, and an antenna. The front-end module may include amplifier circuitry such as a low noise amplifier for amplifying received radio-frequency signals. The low noise amplifier is operable in a non-carrier-aggregation (NCA) mode and a carrier aggregation (CA) mode. The low noise amplifier may include a first input stage, a second input stage, a complementary degeneration transformer, and an input impedance compensation circuit. During the NCA mode, the first input stage is turned on while the second input stage is turned off, the degeneration transformer is controlled to provide maximum inductance, and the compensation circuit is turned on to provide input matching. During the CA mode, the first and second input stages are turned on, the degeneration transformer is adjusted to provide less inductance, and the compensation circuit is turned off.