I am new to analog design and I need to design a galvanic isolator based upon the edge-based communication** described in digital isolator design guide as a part of a task.
How can I start designing this and which simulation programs do I need?
Can the isolator design be realized on PCB or only CMOS?
** I need to isolate an SPI bus using this digital isolator, so any relevant specifications for an SPI Isolator will be OK.
You can design galvanic isolation by just making two circuits that aren't connected to each other.
The difficulty is transferring signals between them without breaking the isolation. The TI parts described in the document you linked are one way of doing that. Optoisolators are another. Transformers are another (for purely AC signals).
How can I start designing this and which simulation programs do I need?
Generally simulators can be useful for predicting how a signaling system works at transferring signals, but they won't do much to tell you whether you've maintained or broken the isolation in your system.
Can the isolator design be realized on PCB or only CMOS?
If you buy the parts from TI (or similar parts from Analog Devices or other vendors) then your signaling across the isolation barrier is implemented in CMOS. But it's also implemented at the board level because you bought the part and put it in your PCB.
You can design your isolator as discrete, just use suitable capacitors (especially with regard with pin clearance and dielectric failure modes) and it's a learning experience. SPICE is fine for simulation, it's nothing more complex than an AC coupled amplifier at the end.
Or much simply you can buy premade isolators; IIRC TI are capacitive and Analog is inductive with chip scale transformers. I've seen other designs in the past with piezoelectric transformers.
Just be aware of the limitation of that kind of isolation barrier: while it's very useful to break ground loops and such kind of common mode issues you (usually) can't relay on that for primary circuit insulation (where you often need 2-4kV to be 'safe'). Optos are for these cases (usually slower and bulkier).
For SPIs I remember parts which casually have 3 signal in on direction and one in the reverse so it's an already solved problem.
