A diode in the base-collector junction of the transistors that prevents them from going into saturation and, therefore, reduces the switching time out of saturation. To perform this function, the diode has to have a low voltage between its terminals; Schottky diodes have this property. The diode is constructed as part of the transistor, resulting in what is called the Schottky transistor.
The low-power Schottky TTL family has higher resistance values than the Schottky TTL. This has the effect of reducing the power consumption and increasing the delay. This family has a good speed-power product and therefore is widely used.
Improvements have been made in the technology producing variations of the Schottky TTL with better speed-power products. Examples of these are Texas Instruments Advanced Schottky (AS), Advanced Low-power Schottky (ALS), and Fairchild Advanced Schottky (FAST). Table 1.1 gives a summary of the power consumption, delay, and speed-power product of all variations.