System Overview

Signal Pathway

Signal Pathway
Signal Pathway in the MCA
(click for larger version)

The signal pathway in the MCA is shown above. The input signal is conditioned so that it can be detected by the analog circuitry. Two separate signal pathways perform pulse timing and height calculation.

To determine when a pulse occurs, the signal is differentiated, and compared with a user-selectable threshold. This produces a logic-level signal. Optionally, if the MCA will be used in conjunction with other equipment, a coincidence or anti-coincidence pulse can be input to the detector. This feature is useful when the output of a second analyzer is only of interest if another trigger occurs - or vice versa. The resulting logic level is latched, and can be polled by the PIC to determine if an pulse occurred. It is also fed into a fast counter (described here), which provides for more accurate flux information.

A peak and hold circuit (described here) is responsible for sampling a voltage pulse at its maximum height. It holds its value until it is sampled by an ADC on the microcontroller and the microcontroller resets a latch.

For more detail on the operation of the PIC microcontroller and the coordination of events in the MCA, please visit the firmware page.