Analog electronics. What are analog components? how do i know whether an Ic is analog or digital?

Question

I'm trying to build a analog dc - dc converter but as i have always dabbled about digital stuff, this has made me baffled. I stared at the Lm109/lm309 data sheet and looked at the schematics. It was all transitors, resistors, diodes. So whats so analog about it? I knew it was under other analog products under http://www.national.com/cat/ but i don't see even the word analog in the whole data. So what is the diff between analog Ic, mixed signal Ic and digital Ic?

Answer 1

A digital IC is an analogue circuit that has a signal in or a combination of signals in at a specific constant voltage but at varied times and that gives you a fixed voltage out. An analogue IC is an IC that uses the same components but it measures a varied voltage signal against another level that is not necessarily constant.  

So if I have a pulse train in of a square wave then it acts as a digital signal. This is how data gets sent around.

If I have a voltage of 2 volts in that I want to compare to 2.4 volts then I would use an analogue IC or OP-amp.

Your analogue to DC converters take a voltage and changes it to a logic combination, say 1010111 for 3 Volts. You get dedicated IC's for this.  

Answer 2

Basically, the digital circuits all start with, or have in their numbers very quickly 74.. or 40.. or 45..  Anything else is probably analog.

Remember, this is a very general rule of thumb.  I am an analog engineer and use both all the time.