How to start with a new & uncommon design?

[justanavgme]

Hi everyone,

I'm an EE student and so far when I was assigned with a commonly known circuit (bandgap, LDO,...), I usually just look it up. I often find useful circuit topologies along with gain or PSRR equations already derived.

But what if I have to work with a new or not very well known circuit which has no proper documentation on how it works? Would you draw the small signal circuit from scratch and start deriving your own equations? What would be your initial approach?

Thank you in advance.

 

[dick_freebird]

I'd capture an application schematic to put
the "guts" in, and take stab at a topology to
work with, netlist it to SPICE and start poking
to see what it does (vs. what it should).

Small signal is not where I'd start, too much
of the universe is anything-but. Though some
prefer to "start small and zoom out" I prefer
the opposite and use SS analysis only for later
parameter simulations where the param of
interest is in fact a small-signal quantity. Too
many encounters with "guess that wasn't small
signal after all" (like transistor saturation, SOI
history effects, hysteretic circuits etc.).

 

[sutapanaki]

If you are given a task to design something from scratch, it will involve obviously some thinking on your part. It is always a good approach to just start. Maybe you start in the wrong way but if you find out that it's wrong you can make corrections, usually incremental corrections that should eventually lead to the final design. Because if you don't start, you don't finish.

 

[deep_sea]

This is a bit difficult because most of the analogue circuits are well known since a long time. Creative designers use "conventional conservative" designs. The conventional circuits is already challenging to implement to meet certain specs or to integrate into a system.
This is why in academia, it is easier to publish circuit ideas in Microwave, Power, Devices journals rather than in circuits like solid state circuits journal (JSSC). It is really difficult to "invent" new circuit. Try to understand what is already there. LDO and bandgap are not trivial as you think. Understand them and try to add your contribution. Your problem is a general one in analogue design world we are all facing.