newbie analog question

I can see that digital design = AND gate, OR Gate, Gates made up from transisters, millions of transisters in a square mm, FPGAs, chips. Designing at gate levels, things so small you can't see, like the FPGA, so small, but weeks of coursework design fits in...

whereas analog, I usually visual it as visible resisters, capitors and inductors, big transisters, big circuits...one lap work was to build an AM receiver, I can see things are pretty big.....

However, from lecture courses about Analog circuits later, we were taught to do calculations on these amplifiers, differential pair, filters, current mirrors, etc... which seem to be working with a lot of transisters, and transisters are very small and resister, capacitors are very big, I'm confused... are there very small transisters for digital and very big transisters for analog?


Please someone help me a little bit here with this one.

We may use Big transistor Inside Digital circuits and also we may use a very small transistor inside Analog circuits it depend on the circuits and on your design

the main idea here is that the transistor size depends on the application and need... if you study about the design of PLL, op amp etc... you would know the number of transistors and transistor sizes.... also in any IC level circuits the capacitors and resistors that you are seeing in discrete form are not used.... MOSFETs are used to realise capacitors and resistors.....

Of course it depends on your design and the problem you have each time.But i can say this:Analog IC cover the 30% of the whole chip so you can have big W/L for critical transistors in order to have no problems such as noise and other.So is up to you

I still can't visualise the size of these things... I know digital circuits are in chips, like FPGAs, and you get big resister and capitors connecting with peripherals, and you call the whole circuit on the PCB the "intergrated circuit" right? but I can't see where these MOSFET lies, in the PCB.... are these Analogue circuits in chips aswell? like the digital FPGAs...

also, what is meant by using big transisters in digital circuits....? any examples?

analog circuits are also there in ICs.... try googling about PLL, op amp, FM transceiver and you will find a lot of ICs related to them.... even the protection circuit of many digital ICs are analog circuits.....

the size of a transistor depends on the parameters we want the transistor to have.... so a comparison between the size of digital and analog transistors and circuits depends on the circuits we are considering....

No dear, Integrated Circuit refers to just the CHIP or MICROCHIP.....

The PCBs that you'd see typically have a number of ICs, resistor, capacitors etc.

FPGA is also a chip. A chip can have millions of transistors.

Usually resistors and capacitor ARE NOT used for IC design.

So gathering my thoughts together, is this correct in a typical PCB?

PCB

- Digital chips (use knowledge from digital design courses)
- Analog chips(use knowledge from analog design courses)
- inter-connecting resistors and capacitors (adjusting the voltage/current for the chips, also filter noise)


Or do you mean

PCB

- IC chips (analogue and digital ALL-IN-ONE chip)[so hard to understand, no lecture courses covered the mix implementations]
- inter-connecting resistors and capacitors

Yes you are right. There are ICs which have both analog and digital components; as well as ICs which are only analog or only digital.

Don't worry! It seems that you're just starting out on Electrical engineering. You will get the hang of it sooner or later. However, most IC designers are either Digital (many of them) and a few are working on the Analog side (which is considered to be a lot more difficult)...and even fewer are MIXED-SIGNAL IC DESIGNERS.....

The elements that you can see and they are big, are discrete type elements,where in IC design you implement CKT in integrated form on a chip,so they are very small.

thanks, you guys are superb. I have been able to learn more with the knowledge within the last year.