Advantages and Disadvantages of TTL Logic Gates

The following are the advantages and disadvantages of TTL logic gates.

Advantages

1.    TTL family is the fastest saturating logic family (working in between the saturation and cut-off modes).  Also, TTL gates are available in a variety of forms, such as high-speed TTL, high-speed Schottky TTL, low-power TTL etc.
2.    Typical supply voltage is only +5 V with a permitted variation of ±0.25 V. At present, TTL gates of 3-volt and even to 1.5-volt supply are possible.
3.    It has good noise immunity. Typical noise-margin is about 0.4 V.
4.    Power dissipation is in the range of several mW only. In the case of low-power Schottky TTL gates, this is less than 2 mW per gate.
5.    TTL gates are compatible with other logic families.
6.    Commercial and military versions of TTL gates are available.
7.    These gates are more freely available in the open market than most other logic families.
8.    Good fan-out; TTL gates can drive up to 10 gates.
9.    TTL gates producing almost all of the logic functions are available in the market.
10.    TTL gates exhibit low output impedance for high/low states.

Disadvantages  

1.      Noise immunity is not very high; so TTL gates cannot be used in applications where large noise voltages exist.
2.      Because of isolation problems, which require more chip space, TTL VLSI circuits are not possible in its conventional form.
3.      Power dissipation of TTL gates is much higher than that of MOS gates.
4.      Cost of TTL gates is higher than that of NMOS/CMOS gates, when MSI and LSI gates are considered.
5.      TTL gates generate transient voltages at switching instants.
6.      Wired-OR capability is not possible for the conventional TTL gates; open-collector gates are required for this application.


No comments:

Post a Comment