NOISE SUPPRESSION CIRCUIT FOR MOBILE TELEPHONE

摘要

A noise elimination circuit of a portable phone is provided to optimize filtering characteristics of an LPF(Low Pass Filter) by using a capacitor whose capacitance is changeable, according to usage environment, thereby effectively suppressing inevitably generated noise as well as white noise. An RF(Radio Frequency) unit(203) processes an RF signal received through an antenna to output the processed signal. A vocoder(205) extracts digital voice information from the outputted signal. A CODEC(Coder Decoder)(207) converts the extracted digital voice information into an analog voice signal to output the converted signal. An LPF(210) filters the outputted analog voice signal, and outputs the filtered signal through a speaker. The LPF(210) consists of a resistor(213) placed between the CODEC and a speaker, a capacitor(217) between the resistor(213) and the speaker and a varactor(215) between the resistor(213) and the capacitor(217).