https://github.com/mtmccrea/Hilbert/issues/17 > Bernie Hutchins provides a discussion of PDN design here: > > [Electronotes 168 90 Degree Phase Differencing Networks - 7 pg](http://electronotes.netfirms.com/EN168-90degreePDN.PDF) > > Offers a method to calculate poles for arbitrary _Order_ and _Bandwidth_. >