Figure 2a and b—The 2-D tetralateral type of PSD has a single resistive layer on only one surface. The bias electrode is a dedicated lead on the rear of the substrate; it makes biasing simple. A higher reverse bias causes a reduction in the junction capacitance and higher frequency response, but also causes higher dark current. This type of PSD has the worst accuracy—typically a 3 to 6% position error near the perimeter of the device.