90 degree phase shift
You can generate fixed delays using R-C circuits and voltage comparators, like this:







simulate this circuit &ndash; Schematic created using CircuitLab

Adjust R1 and/or C1 to get the delay you want, which is 100 ns in this case. R2 and R3 establish a switching point at exactly Vcc/2, which is important in order to get equal delays on the rising and falling edges.

Note that you can get a 1% resistor with the value of 143 &Omega;, but then the overall accuracy of your delay would depend on the precision of the capacitor.