We design a digital pre-amplifier which can be directly connected to an electret microphone. The amplifier can convert analog signals into digital signals, has a wide voltage swing and low power consumption, as is required in portable applications. Measurement results show that the dynamic range of the digital pre-amplifier reaches 88 dB, the equivalent input referred noise is 5 μVrms, the typical power consumption is 540 μW, and in standby mode the current does not exceed 10 μA. Compared with an analog microphone, an electret microphone with digital pre-amplifier offers a better SNR, higher integration, lower power consumption, and higher immunity to system noise.