A power detector has a signal input terminal, N limiting amplifiers, N rectifiers and a signal output terminal. N is an integer greater than 1. The signal input terminal receives an input signal, and the signal output terminal outputs a detection signal. The N limiting amplifiers generate N amplified signals according to N attenuated signals having different attenuation. Each limiting amplifier receives one of the N attenuated signals and outputs one of the N amplified signals. Each rectifier receives a corresponding amplified signal and outputs a rectified signal. The detection signal is associated with the sum of N rectified signals outputted from the N rectifiers, and all transistors of the power detector are bipolar junction transistors.