Resistor-transistor logic

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Resistor-transistor logic (often referred to by its acronym, RTL) was the earliest logic family using bipolar transistors; it was later essentially completely replaced by the later diode-transistor logic.

The name comes from the fact that the logic functions were performed by resistor networks; the signal-amplification was performed by a transistor.

The use of resistors was good in the pre-IC stage (when discrete transistors were expensive), but it limited the number of inputs. The use of resistors for the logic network also led to minimal noise immunity, probably the biggest drawback of DTL.

Is it notable as being the logic family in the first integrated circuits, produced by Fairchild Semiconductor; those ICs were used in the Apollo Guidance Computer.

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