DC amplifier

Japanese: 直流増幅器 - ちょくりゅうぞうふくき（英語表記）DC amplifier

Audio signals do not contain signal components below a few tens of hertz and can be transmitted through a capacitor. In contrast, measuring instruments and other devices must amplify signals that contain a direct current component that does not change over time, and such amplifiers are called DC amplifiers. There are two types of DC amplifiers: those that use a direct-coupled multistage amplifier to amplify the signal as is, and those that use a modulated DC amplifier to first modulate the signal with a high-frequency carrier wave, amplify it with an AC amplifier, and then demodulate it using synchronous rectification with the same carrier wave to return it to a signal that contains a DC component.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

音声信号は数十Hz以下の信号成分はなく，コンデンサーを通して伝送できる。これに対して，測定器などでは時間的に変化しない直流分を含む信号を増幅しなければならず，このような増幅器を直流増幅器と呼ぶ。直流増幅器には直結形の多段増幅器で信号をそのまま増幅するものと，信号をいったん高周波の搬送波で変調して交流増幅器で増幅し，同じ搬送波による同期整流を用いて復調して直流分を含む信号に戻す変調形直流増幅器の2種類がある。

出典　株式会社平凡社世界大百科事典第２版について　情報

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