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Capacitive coupling is also known as AC coupling and the capacitor used for the purpose is also known as a DC-blocking capacitor. A coupling capacitor's ability to prevent a DC load from interfering with an AC source is particularly useful in Class A amplifier circuits by preventing a 0 volt input being passed to a transistor with additional ...
The AC-coupled circuit acts as a level-shifter amplifier. Here, the base–emitter voltage drop is assumed to be 0.65 volts. The input capacitor C removes any DC component of the input, and the resistors R 1 and R 2 bias the transistor so that it will remain in active mode for the entire range of the input.
Conventional vacuum tube amplifier designs rely upon an output transformer to couple the amplifier's output stage to the loudspeaker. Instead, OTLs use one of two primary methods for output stage coupling: direct coupling (DC) or capacitive coupling (AC).
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude (magnitude of the voltage or current) of a signal applied to its input ...
The direct-coupled amplifier was influential in the development of Fairchild's uA709 operational amplifier by Bob Widlar, which Noyce knew about as he was one of the founders of Fairchild Semiconductors. The direct-coupled amplifier is also the basis for Philco's Mark I hearing aid, which used the circuit built with silicon alloy transistors.
That is, an active load imposes less restriction on the output voltage swing. Notice that active load or not, large AC gain still is coupled to large AC output resistance, which leads to poor voltage division at the output except for large loads R L ≫ R out. For use as a current buffer, gain is not affected by R C, but output resistance is.
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