Integrated circuits and logic families
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Integrated circuits and logic families book
The output resistance of a saturated transistor (Tr3 in Figure 15.1) is inherently low (about 10 ohms typically), providing the desired low output resistance when the output goes LOW. When the output is HIGH, Tr4 is active and provides the low output resistance characteristic. In IC form, TTL gates are small, reliable and cheap; because of their excellent characteristics they are used in a great variety of IC devices.