why do we need rail-to-rail input stages?

[yonutz88]

does anyone know some books in which is explained the need for rail-to-rail inputs and outputs? thanks

 

[rhaynes]

I don't know of any books but having R-R I/O can be helpful for single supply operation. One example is for current measurement or control where one end of the sense resistor is tied to either ground or power. Having a R-R input stage makes the design a breeze.

In contrast to R-R inputs which are specified to work at the rail which is a black and white specification, a R-R output I would say is more of a marketing term. If any load what so ever is applied to the output it can not go rail to rail. So how close it gets to the rail with a specified load is the real specification and those specs vary all over the place.

Ray

 

[kak111]

Here is Microchip`s analog design note, about

What Does “Rail-to-Rail” Operation Really Mean?

https://ww1.microchip.com/downloads/en/DeviceDoc/adn009a.pdf

Regards KAK

 

[BradtheRad]

1.

Binary operation works best when you have extremes between a hi and low signal.

So rail-to-rail operation is preferable in that case. Not easy to achieve since output components don't have zero ON-resistance.

2.

Or with audio amplifiers, you want linear operation, and across the maximum range you can get.

This is assisted by output components with a minimum of 'ON' resistance. In other words, which more closely approach rail-to-rail operation.