A configurable calculating circuit includes a multiplexer, a mixer and an accumulator. The multiplexer is for receiving input signals including at least a first and a second input signals, and selectively outputting at least one of the input signals. The mixer is for mixing a selected input signal outputted from the multiplexer with a local oscillation signal to generate a mixed signal. The accumulator is for accumulating the mixed signal to generate an accumulated signal. When the configurable calculating circuit is operated under a first mode, the multiplexer selects the first input signal, and the accumulator performs a first accumulating operation upon the mixed signal; and when the configurable calculating circuit is operated under a second mode, the multiplexer selects the second input signal, and the accumulator performs a second accumulating operation, different from the first accumulating operation, upon the mixed signal.