The demodulator is an important component of a modulated DC amplifier circuit. It restores the amplified AC voltage to a DC voltage, whose magnitude and polarity correspond to the amplitude and phase of the AC voltage.



The modem we often refer to is actually the abbreviation for modulator and demodulator, which is called a modem in Chinese. Some people affectionately call it "cat" based on the homophonic sound of the modem. We know that information in computers is composed of digital signals of "0" and "1", while what is transmitted over telephone lines can only be analog electrical signals. So, when two computers need to transmit data over a telephone line, a device is needed to handle the conversion between digital and analog. This analog-to-digital converter is the modem we are going to discuss here. When a computer sends data, the modem first converts the digital signal into the corresponding analog signal, which is called "modulation". Before the modulated signal is transmitted through a telephone carrier to another computer, it also needs to be restored to a digital signal that can be recognized by the computer through the receiver's modem. This process is called "demodulation". It is through such a digital to analog conversion process of "modulation" and "demodulation" that remote communication between two computers is achieved.

As an electronic device, the power supply principle of a modem mainly follows the working principle of a general electronic device power supply. The function of a power supply is to convert other forms of energy (such as AC power) into electrical energy and provide stable voltage and current to the internal circuits of the modem.