# Signal to Noise Ratio [closed]

Please explain about Vih,Vil,Voh and Vol and how they are relaed to SNR? Do we have to take care of these parameters when we are selecting any peripherals to interface with master controller?If yes than what will be the limits?

• Obviously an homework without showing any effort so far. This is off topics here. sorry – Blup1980 Jul 14 '14 at 10:55

The main ones to consider are $V_{IH}$ and $V_{IL}$. These are the logic HIGH and logic LOW input voltage thresholds. Anything above $V_{IH}$ is considered a logic HIGH, and anything below $V_{IL}$ is considered a logic LOW.
The space between $V_{IH}$ and $V_{IL}$ is called the noise margin and any signal within this region is ignored.
The corresponding output values $V_{OH}$ and $V_{OL}$ of a device feeding $V_{IH}$ and $V_{IL}$ must therefore fall reliably in the $V_{IH}$ and $V_{IL}$ regions. The more fully into those regions, and away from the noise margin the voltages are the better the immunity to noise.
For instance, if you have a device with a $V_{IH}$ of 3V, and a device which outputs a $V_{OH}$ of 5V, you have 2V of noise immunity before it reaches the noise margin. However, if $V_{OH}$ is only 3.2V then you only get 0.2V of noise immunity.