These Schottky-clamped circuits are designed to be used in high-performance memory-decoding or data-routing applications, requiring very short propagation delay times. In high-performance memory systems these decoders can be used to minimize the effects of system decoding. When used with high-speed memories, the delay times of these decoders are usually less than the typical access time of the memory. This means that the effective system delay introduced by the decoder is negligible.
The DM74ALS138 decodes one-of-eight lines, based upon the conditions at the three binary select inputs and the three enable inputs. Two active-LOW and one active-HIGH enable inputs reduce the need for external gates or invert ers when expanding. A 24-line decoder can be imple mented with no external inverters, and 32-line decoder requires only one inverter. An enable input can be used as a data input for demultiplexing applications.
This decoder/demultiplexer features fully buffered inputs, presenting only one normalized load to its driving circuit. All inputs are clamped with high-performance Schottky diodes to suppress line-ringing and simplify system design.
■ Designed specifically for high speed:
Data transmission systems
■ 3- to 8-line decoder incorporates 3 enable inputs to
simplify cascading and/or data reception
■ Low power dissipation…23 mW typ
■ Switching specifications guaranteed
over full temperature and VCC range
■ Advanced oxide-isolated, ion-implanted Schottky TTL