A circuit board which has a high speed digital circuit in close proximity to a sensitive analog structure has a grounded, conductive band interposed between them and a ground plane with two separate, grounded portions, with a first of the portions underlying the digital circuit and a second portion underlying the analog structure. In an exemplary embodiment, the circuit board has a high density of analog-to-digital converter integrated circuits, each with two analog input signals and ten parallel high speed digital output signals corresponding to each input signal. A grounded, conductive band is placed on the board between the inputs and outputs of the integrated circuit, and a ground plane is provide which has separate, interleaved analog and digital areas, with the digital area underlying only portions of the board having digital signals and structures and the analog area underlying only portions of the board having analog signals and structures.