A signal converter includes a signal converting unit and a compensation unit. The via is formed through a dielectric layer and a barrier layer that are disposed over a metal-containing trace, pad, or other such circuitry, wherein the metal-containing trace, pad, or other circuitry is disposed on a semiconductor substrate. According to an input control signal, a focus actuator actuates the pickup head to keep it substantially at the focal distance. Then, the pinched-off portion of the vessel is pressed so as to move it from a first position wherein the portion is convex to a second position wherein the portion is concave. A transport signal is also evaluated and a transport signal validity indicator value is then created.