What is the necessity of Interfacing in digital ICs and what are the points to be kept in view, while interfacing between TTL gate and CMOS gate?

Ans:

To realize the optimum performance in digital system, the device from more than one logic families can be utilized, that takes advantages of the better characteristics of each logic families. For illustration, CMOS logic ICs can be utilized in those parts of the system where low power dissipation is essential, and TTL can be utilized where high speed of operation is needed. While CMOS derives TTL, the subsequent conditions are essential to be satisfied.

V_OH(CMOS) ≥ V_IH(TTL)

V_OL(CMOS) ≤ V_IL(TTL)

-I_OH(CMOS) ≥ NI_IH(TTL)

-I_OH(CMOS) ≥ -NI_IL(TTL)

Figure 1: TTL-to-CMOS interfacing using pull-up register.

Figure 2: CMOS-to-TTL interfacing using a CMOS buffer IC