Resistor–transistor logic

The resistor - transistor logic, English resistor transistor logic (RTL), a logic family is no longer used in the electronics.

Logic gates and functions were realized by the combination of resistors and subsequent amplification by transistors. The output of these circuits can control only three inputs from other circuits in the TTL gate the figure is about ten. This maximum possible degree of branching is called fan-out.

The RTL was the first form of digital electronic circuits, which was developed in the 1950s by Texas Instruments specifically designed for use in the field of seismology. The Massachusetts Institute of Technology (MIT ) designed with this technique, the Apollo Guidance Computer, which was used aboard the Apollo spacecraft.

RTL 2 NOR gates

Construction

The diagram at right shows a NOR operation with two inputs of type MC717 It has a power loss PV of 5 mW and a duration of 25 ns tpd on.

Located on an input U1 or U2 high level, the corresponding transistor is conductive and thereby connected the output to low level. Each input has an associated transistor, transistors share a common collector resistor Rc. Therefore, the output voltage Vout is highly dependent on the load at the output, resulting in a lower fan-out results. The transistors are switched in the saturated state due to the low base resistances R1 and R2. Thus, the switching times are relatively long, but the arrangement against fluctuations between transistors is insensitive because the transistors are turned on even at low gain.

Due to the above disadvantages RTL circuits are no longer used.