Editing Resistor–transistor logic (section)

=== RTL inverter ===

A bipolar [[Transistor#Transistor as a switch|transistor switch]] is the simplest RTL gate ([[Inverter (logic gate)|inverter]] or NOT gate) implementing [[logical negation]].<ref>[http://www.play-hookey.com/digital_electronics/rtl_gates.html Resistor-Transistor Logic] {{Webarchive|url=https://web.archive.org/web/20181002181106/http://www.play-hookey.com/digital_electronics/rtl_gates.html |date=2018-10-02 }} explains the basic RTL gates and gives some useful calculations</ref> It consists of a [[Common emitter|common-emitter stage]] with a base resistor connected between the base and the input voltage source. The role of the base resistor is to expand the very small transistor input voltage range (about 0.7 V) to the logical "1" level (about 3.5 V) by converting the input voltage into current. Its resistance is settled by a compromise: it is chosen low enough to saturate the transistor and high enough to obtain high input resistance. The role of the collector resistor is to convert the collector current into voltage; its resistance is chosen high enough to saturate the transistor and low enough to obtain low output resistance (high [[fan-out]]).