Intuitive Analog Circuit Design

Reverse-Active Region

In the forward-active region, the base-emitter junction is forward biased and the collector-base junction is reverse biased. We could just as easily operate the transistor with the collector-base junction forward biased, and the base-emitter junction reverse biased. This mode of operation is called the reverse-active region, and analysis is exactly analogous with the forward-active region, with the roles of the collector and emitter reversed. [2] The carrier profile is as shown in Figure 10-3. The charge control equations in the reverse-active region are:



Figure 10-3: Excess carrier concentration for NPN transistor in reverse-active region. Note that in the reverse-active region the collector-base junction is forward biased and the base-emitter junction is reverse biased.

Transistors are optimized to run in the forward active region. When operated in the reverse active region, as might be expected, transistor parameters such as speed and ? F are degraded.

[2] The charge stored in the base in the reverse-active region is q R.

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