Comparison of Logic Families:

The following are the Comparison of Logic Families are

1. RTL and DTL families have become obsolete because of their low speed, high power dissipation, and low fan-out.

2. TTL is the most popular general purpose logic family. It is available in seven different series with a wide range of operating speed, power dissipation and fan-out. There are a large number of functions in SSI and MSI available in TTL.

TTL ICs are available with totem-pole output (which reduces speed-power product), open-collector output (which makes possible wired-AND connection and bus operation), and tri-state (TSL) outputs (which are ideally suited for bus operation).

3. HTL are best suited for an industrial environment where electrical noise level is high.

4. ECL is the fastest logic family. Its main drawbacks are : low noise-margins and high power dissipation. For interfacing other logic families level-shifting networks are required.

5. I2L is the only saturated bipolar logic family suitable for LSI because of small silicon chip area requirement and low power consumption. Because of low voltage require­ment, it is highly suitable for battery operated systems.

6. MOS devices occupy a very small fraction of silicon chip area as compared to bipolar devices and need very small power. So, MOS logic is most popular logic for LSI. The main disadvantage of MOS logic family is low speed, which is being improved upon by improvements in the technology of MOS fabrication.

7. CMOS has the lowest speed-power product and need very small power. CMOS is increasingly becoming popular in the area of MSI and LSI.

Table 47.5 gives the values of different parameters for comparison of logic families.

Comparison of Logic Families