Abstract: The switchable up-conversion loop device for a transmitting stage of a mobile phone having multiple transmitting frequency bands includes a phase detector (21) for generating a phase detector output signal in response to a phase difference between an input signal and a mixing product signal, multiple switchable voltage controlled oscillators (35, 37; 100, 101, 102; 111, 112; 120), each connected to the phase detector (21) and each generating an output oscillating signal, the frequency of which depends on the phase detector output signal, and a coupling device (44; 110; 119; 121) for coupling the output oscillating signal to a mixer (26) for mixing said output oscillating signal with a locally generated oscillating signal to produce the mixing product signal.