Electronic – Categorizing ICs as digital or analog


I'm new to electronics and trying to understand the difference between analog and digital ICs. My understand of analog and digital signals is up to scratch but I am struggling to categorize ICs into either analog or digital based on their function.

After digging around in datasheets and looking around online I am becoming more confused! I'm hoping someone can point me in the right direction or re-align my thinking so I can figure out what these ICs are without having to ask about individual components.

My confusion mainly comes from looking at functional block diagrams in datasheets.

For example, if we look at this Half-Bridge Gate Driver, http://www.ti.com/lit/ds/symlink/ucc27211a.pdf the schematic on pg 13 shows a diagram containing logic gates (digital signals) and what seems to be amplifiers of some sort(?), a diode, Schmitt triggers buffers (?), which are analogue components, so is this IC a digital or analog IC?

There are also some functional blocks; level shift and UVLO, I'm not even sure where to start with these!

Also, I seem to have been convinced that transistors are analogue components, but these are then use to create a logic gate. The line between analog and digital is becoming ever more blurry, any help is greatly appreciated.

Thanks in advance.

Best Answer

It's blurry because it is not black and white, or rather there is a huge grey scale between black and white that sometimes can be considered analog and other times can be considered digital depending on the application.

In reality everything, except perhaps at the atomic level, is actually analog.

Digital circuits are actually analog comparators, usually with some hysteresis, that makes them flip their outputs depending on what the input voltage or current does.

Once you have such a "gate" you can combine them in an infinite number of ways to produce more complex logic functions.

Some devices, like simple latches etc are purely logic gates. Others are hybrids that contain both "digital" and analog circuits.

A simple transistor can be used either as a current amplifier, or it can be used as a switch. Or more accurately, a transistor has three states, Saturated (ON), Reverse Biased (OFF), and Linear (neither on nor off). As such, which mode you are using is dictated by how it is driven and arranged. When you are using it as a switch, using the On and Off states, the transistor always has to goes through that linear region during the transition. So yes, the definition is blurry.

As for your indicated device. It falls into that hybrid category. It takes digital inputs and outputs analog voltages based on those inputs and what the load is doing.

In the end, as Andy pointed out, it usually doesn't matter what you call it.

There are some exceptions though. A good example of that is a multiplexer, a device that channels inputs to outputs based on come control signals. A digital multiplexer is very different from an ANALOG multiplexer.