Increase the Noise Immunity

[PrescottDan]

Why would a designer want to increase the Noise Immunity of logic signals? for the reset signal?

How do you increase the noise immunity for logic signals?

 

[rkt_167]

Noise Immunity of logic signal are increased to avoid errors in output. e.g if 001 is received as 101 which has entirely different meaning.
In analog signal we generally use various filters to filter out various kind of noise and In case digital signal we generally go with hard and soft decision making to avoid error. just check https://www.gaussianwaves.com/2009/12/hard-and-soft-decision-decoding-2/

 

[chuckey]

If you are designing a piece of kit which is going to be used in an electrically noisey enviroment, such as an arc welder controller, high noise immunity is an advantage. It is set by the characteristics of the logic family used. Old TTL, had a max "0" of .8V, and a minimum "1" of 2.4V, So a 1.6V noise pulse could turn a "1" into a "0". Modern CMOS (4000 series) running on 15V has a noise immunity of 12V. In the 1960s, Mullard made a series called Norbit , which had a noise immunity of 20V.
So if you really want high noise immunity, you need to build your own logic circuits out of transistors etc. Or you could use an external high voltage logic level, say 1 = 50V (>48) and a 0 = 0V (<1V) then build interfaces to get these levels back to that of a normal logic family.
Frank