A backplane has through holes for conductors to project through the backplane in arrays corresponding to respective circuit boards arranged along the front side of the backplane. The method includes the steps of forming a shallow first-type well layer, a second-type well layer and a deep first-type well layer over a substrate, forming stack gates over the shallow first-type well layer and finally forming source terminals and drain terminals. The method also includes determining a one-sided power spectral density from the received signals.