An apparatus for measuring Output Voltage characteristics on a dynamic logic signal at an output of a device under test includes a comparator for comparing the voltage at the output with a threshold voltage to generate a control signal. Also provided herein are vectors and host cells comprising those nucleic acid sequences, chimeric polypeptide molecules comprising the polypeptides of the present invention fused to heterologous polypeptide sequences, antibodies which bind to the polypeptides of the present invention and to methods for producing the polypeptides of the present invention. This makes it possible to detect spherical aberation signals more stably. The dopant concentration in the second body region is greater than the dopant concentration in the first body region.