Editing Resistor–transistor logic (section)

== Speeding up RTL ==

Various companies have applied the following speed-up methods to discrete RTL.

Transistor switching speed has increased steadily from the first transistorized computers through the present.  The ''GE Transistor Manual'' (7th ed., p.&nbsp;181, or 3rd ed., p.&nbsp;97 or intermediate editions) recommends gaining speed by using higher-frequency transistors, or capacitors, or a diode from base to collector ([[Baker clamp|parallel negative feedback]]) to prevent saturation.<ref name=Cleary>
{{cite book
  | editor = Cleary, J. F.
  | title = ''GE Transistor Manual''
  | edition = 3rd–7th
  | publisher = General Electric, Semiconductor Products Department, Syracuse, NY
  | year = 1958–1964 }}
</ref>

{{anchor|RCTL}}Placing a capacitor in parallel with each input resistor decreases the time needed for a driving stage to forward-bias a driven stage's base-emitter junction.  Engineers and technicians use "RCTL" (resistor-capacitor-transistor logic) to designate gates equipped with "speed-up capacitors".  The Lincoln Laboratory [[TX-0|TX-0 computer's]] circuits included some RCTL.<ref name=Fadiman>
{{cite book | last=Fadiman | first=J. R. | year=1956 | title=TX0 Computer Circuitry  | publisher = MIT Lincoln Laboratory | url=http://bitsavers.org/pdf/ibm/140x/1401_CE_Drws_1962.pdf | accessdate=2011-09-09 }}
</ref> However, methods involving capacitors were unsuitable for integrated circuits.{{Citation needed|date=April 2011}}

Using a high collector supply voltage and diode clamping decreased collector-base and wiring capacitance charging time.  This arrangement required diode clamping the collector to the design logic level.  This method was also applied to discrete DTL ([[diode–transistor logic]]).<ref name=DEC>
{{cite book | year=1967 | title=The Digital Logic Handbook Flip Chip Modules | publisher = Digital Equipment Corporation| url=http://www.bitsavers.org/pdf/dec/handbooks/ |id=1750·3/67 |via=Bitsavers | accessdate=2008-03-08 }}
</ref>

Another method that was familiar in [[discrete-device]] logic circuits used a diode and a resistor, a germanium and a silicon diode, or three diodes in a negative feedback arrangement. These diode networks known as various [[Baker clamp]]s reduced the voltage applied to the base as the collector approached saturation. Because the transistor went less deeply into saturation, the transistor accumulated fewer stored charge carriers. Therefore, less time was required to clear stored charge during transistor turn off.<ref name=Cleary/> A low-voltage diode arranged to prevent saturation of the transistor was applied to integrated logic families by using [[Schottky diode]]s, as in Schottky [[Transistor–transistor logic|TTL]].