Hi,

>>I'm looking for a means of phase shifting a square wave clock pulse by
>>90 degrees.
>
>If it is a constant frequency, then just add a delay, of t/4, where t is
>the period of the pulse.
>
>If it could be some unknown frequency, it's more difficult- more details
>would be needed.
>
>Nigel

A pll (eg 4046) with XOR phase comparator could do it.

Les