ABSTRACT
Digital devices are constrained to two stable operating regions separated by a transition region through which the operating point may pass but not remain. Prolonged operation in the transition region does not cause harm to the devices, it simply means that the resulting outputs are unspecified. Digital logic components were the earliest commercially produced integrated circuits. Resistor-transistor logic and a speedier variant resistor-capacitor-transistor logic were introduced in the early 1960s by Fairchild Semiconductor Diode-transistor logic was introduced a few years later by Signetics Corporation. First introduced in the 1960s, transistor-transistor logic (TTL) was the technology of choice for discrete logic designs into the 1990s, when complementary metal oxide semi-conductor equivalents gained ascendancy. Because the internal switching dynamics differ and because the pull-up and pull-down transistors have different current drive capabilities, TTL parts show a longer propagation time when driving the output from low to high than from high to low.
