RTL is the acronym for resistor transistor logic or logic-transistor resistance. It was the first logic family to appear before the integration technology. Belongs to the category of bipolar logic families, or involve the existence of two types of carriers: electrons and holes.
This type of network, presents the phenomenon called power grab that occurs when multiple transistors are coupled directly and input characteristics differ slightly from each other. Then one of them lead before the others placed in parallel (monopolize the flow), preventing the proper functioning of the rest.
Figure 1, is represented, by way of example, a NOR logic gate and its corresponding electronic circuit in RTL logic.
It can be seen as in series with the base of each transistor is placed a compensation resistor (Rc) of a high enough value for the current distribution is more equal as possible and not occurrence of the phenomenon described above.
This circuit arrangement has the disadvantage that with the addition of resistance Rc increases the switching delay, having to be loaded and unloaded through the same input capacitance of transistors but on the other hand, has the advantage of increased output factor (fan-out). Therefore, in the design of these circuits is necessary compromise between output and factor switching delay. Normal values \u200b\u200bare output by a factor of 4 or 5, with a switching delay of 50 nanoseconds.
On the other hand, has a relatively poor noise immunity. The noise margin voltage to the voltage logic 0 threshold is about 0.5 volts, but voltage logic 1 to the threshold voltage is only about 0.2 volts.
may improve travel time by adding a capacitor in parallel with each of the resistors Rc, which would get a new logic family, to be called RCTL. However, the large number of resistors and capacitors difficult to integrate so much the technique, such as RTL, not used in modern designs but can still be found in very old equipment.
The emergence of DTL circuits, with their greater speed and noise immunity meant the end of the RTL circuit.
Yoseph 18257871 ESS SECTION 2 CI BUITRAGO
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