A femoral distractor includes a top post for positioning under a patient’s knee and a bottom pin for fixed attachment to a hospital bed rail. A common N layer serves to provide both the separate N cathode regions of the zener diode and the separate bottom electrode N region of the capacitor. The gap, the spacer portions and the layers may have insulating andor conducting portions as needed. The rear cover can be integral with the ring, or formed separately. Therefore, the present invention does not need a large size of the storage in which both the bias current and the modulation current are stored as a table.