Editing Resistor–transistor logic (section)

== Limitations ==

The disadvantage of RTL is its high power dissipation when the transistor is switched on, by current flowing in the collector and base resistors. This requires that more current be supplied to and heat be removed from RTL circuits. In contrast, TTL circuits with "[[Totem pole output|totem-pole]]" output stage minimize both of these requirements.

Another limitation of RTL is its limited [[fan-in]]: 3 inputs being the limit for many circuit designs, before it completely loses usable noise immunity.{{Citation needed|date=January 2008}} It has a low [[noise margin]]. Lancaster says that integrated circuit RTL NOR gates (which have one transistor per input) may be constructed with "any reasonable number" of logic inputs, and gives an example of an 8-input NOR gate.<ref name=Lancaster>
{{cite book
|author=Donald E. Lancaster
|title=RTL cookbook
|year= 1969
|isbn=0-672-20715-X
|publisher=Bobbs-Merrill Co. (or Howard W Sams)
|url=http://www.alibris.com/booksearch?qsort=p&siteID=BMAI54k.xMY-6bJvSC2hb2j9kKSb5V.rLA&qtit=RTL+Cookbook}}
</ref>

A standard integrated circuit RTL NOR [[Logic gate|gate]] can drive up to 3 other similar gates.
Alternatively, it has enough output to drive up to 2 standard integrated circuit RTL "buffers", each of which can drive up to 25 other standard RTL NOR gates.<ref name=Lancaster/>