Consider an npn transistor circuit. During the positive half-cycle of the signal, the base is positive with respect to the emitter and hence the base-emitter junction is forward biased. This causes a base current and much larger collector current to flow. The positive half-cycle of the signal is amplified in the collector. During the negative half-cycle, the base-emitter junction is reverse biased and hence no current flows. No output flows during the negative half-cycle of the signal. Thus the positive-only amplified output is unfaithful.
A sufficent battery source in the base circuit keeps the input circuit forward biased even during the peak of the negative half-cycle. When no signal is applied, a DC current I C will flow in the collector circuit due to the battery. This is known as zero signal collector current.
The value of zero signal collector current should be at least equal to the maximum collector current due to AC signal alone.
Famous quotes containing the words proper, signal, collector and/or current:
“My mind rebels at stagnation. Give me problems, give me work, give me the most abstruse cryptogram, or the most intricate analysis, and I am in my own proper atmosphere. I can dispense then with artificial stimulants. But I abhor the dull routine of existence. I crave for mental exaltation.”
—Sir Arthur Conan Doyle (1859–1930)
“Certainly the effort to remain unchanged, young, when the body gives so impressive a signal of change as the menopause, is gallant; but it is a stupid, self-sacrificial gallantry, better befitting a boy of twenty than a woman of forty-five or fifty. Let the athletes die young and laurel-crowned. Let the soldiers earn the Purple Hearts. Let women die old, white-crowned, with human hearts.”
—Ursula K. Le Guin (b. 1929)
“Though collecting quotations could be considered as merely an ironic mimetism—victimless collecting, as it were ... in a world that is well on its way to becoming one vast quarry, the collector becomes someone engaged in a pious work of salvage. The course of modern history having already sapped the traditions and shattered the living wholes in which precious objects once found their place, the collector may now in good conscience go about excavating the choicer, more emblematic fragments.”
—Susan Sontag (b. 1933)
“Liberty, as it is conceived by current opinion, has nothing inherent about it; it is a sort of gift or trust bestowed on the individual by the state pending good behavior.”
—Mary McCarthy (1912–1989)