An exemplary signal amplification circuit includes an input stage, a plurality of output stages and a selecting stage. The input stage has an input node for receiving an input signal and an output node for outputting an intermediate signal. The output stages are coupled to a plurality of output ports of the signal amplification circuit, respectively. Each output stage generates a corresponding processed signal to a corresponding output port according to a gain and the intermediate signal when enabled. The selecting stage selectively couples the output node of the input stage to at least one of the output stages. The signal amplification circuit outputs a first number of processed signal(s) when operated under a first operational mode, and outputs a second number of processed signal(s) when operated under a second operational mode.