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	WHAT'S YOUR ENGINEERING QUOTIENT?
Problem 8—What is "base width modulation" in transistors? Answer Base width modulation, also called the Early effect, is a variation in the current transfer characteristics of a transistor as a function of V_CE. In the active region, the base-emitter junction of a transistor is forward biased and the base-collector junction is reverse biased. The width of the base-collector depletion region increases with V_CE. Because the base region is usually more lightly doped than the collector region, the depletion region occupies more space in the base than in the collector, reducing the effective width of the base region. This reduces the rate of carrier recombination in the base region, in effect making the transistor more efficient, with a higher h_FE. This causes the collector current to vary slightly with collector voltage, and makes the lines slope slightly in the typical graph of transistor characteristics. When modeling a transistor, the Early effect can be treated as a slight variation in V_BE as a function of V_CE. Typically, DV_BE » 0.0001 × DV_CE. Contributor: Naveen P N 7-01 For questions or comments about Test Your EQ, e-mail eq@circuitcellar.com.