Change phase of the output of a buffer I have a question about changing the phase of a buffer.

Question - How to change the output phase of a buffer by 90 degrees, 180 degrees, and 270 degrees?

I know to change the phase by 180 degrees, we just invert the signal using an inverter. But what about changing it by 90 degrees?

Thank you for your help!
If you are referring to a buffer as in a logic gate, this question may be more appropriate on the electronics stack exchange site but here are some suggestions. 

If it is a logic gate, you must be referring to a fixed frequency clock, and shifting the phase for this is quite trivial. Here are some approaches to doing this:

For 180° simply invert with a not gate (inverter).

For 90° and 270° you can double the frequency with a frequency doubler and then invert the 2x clock and then divide by 2 with a flip flop (since it's output changes state on each rising edge). You need to gate the reset on the divide by twos with your original signal to ensure a consistent phase state (either 90° or 270°)

For 90° you can phase-lock a like frequency VCXO using an XOR gate as the phase detector which will have a lock point at 90°, invert this to get 270°.

For 90° you can implement a delay lock loop (similar to above but with a voltage variable delay line and compare one clock output to the delayed one with the xor gate, integrate it's output and use that to control the delay line for a first order DLL which will lock to 90°)

For non precise (temperature sensitive) approximate phase shifts, cascade buffers with RC filters in between.

For variable phase shifts there are plenty of delay lines on the market: https://www.digikey.com/products/en/integrated-circuits-ics/clock-timing-delay-lines/688