The invention relates to a fabrication apparatus for fabricating a layer structure comprising at least a patterned first layer on a substrate. In order to detect whether a value has exceeded or is below a threshold for the acceleration to which objects have been subjected in the past, i. If an entry is not present in the table for the particular flow, the packet is forwarded to the CPU to be processed. In some embodiments in which the op-amp is auto-zeroed during some or all of the sampling phases, the accumulation circuit may include a holding capacitor that, during an auto-zeroing process, holds a value output by the op-amp during a prior transfer phase. A refrigeration subsystem is mounted directly adjacent the dispense font to provide a controlled flow of refrigerant to the open space within the font. The channel correlator or channel-matched filter despreads the subtracted signal.