Diode–transistor logic

The turned on transistor's collector current will then pull the output Q low (logic 0; VCE(sat), usually less than 1 volt).

Q1's collector current will be essentially zero, so R2 will pull the output voltage Q high (logic 1; near V+).

[citation needed] The designers of the 1962 D-17B guidance computer used diode-resistor logic as much as possible, to minimize the number of transistors used.

[6] CTDL avoided the level shifting stage (R3 and R4) by alternating NPN and PNP based gates operating on different power supply voltages.

In an integrated circuit version of the DTL gate, R3 is replaced by two level-shifting diodes connected in series.

Also the bottom of R4 is connected to ground to provide bias current for the diodes and a discharge path for the transistor base.

In 1964, Fairchild released the 930-series DTμL micrologic family that had a better noise immunity, smaller die, and lower cost.

When it comes out of saturation (one input goes low) this charge has to be removed and will dominate the propagation time.

His patent also showed how the Schottky transistor could be used in DTL circuits and improve the switching speed of other saturated logic designs, such as Schottky-TTL, at a low cost.

Schematic of basic two-input DTL NAND gate. R3, R4 and V− shift the positive output voltage of the input DL stage below the ground (to cut off the transistor at low input voltage).
NAND and NOR DTL logic circuits as used on IBM 608 cards. The PNP and NPN transistor symbols are those used by IBM. [ 1 ]
A digital clock made only with discrete transistors, diodes and resistors, no integrated circuits. This clock uses 550 switching diodes and 196 transistors to divide 60 Hz power-line frequency down to one pulse per second and provide a display of hours, minutes and seconds.