Blue Processing Electronics


The signal from the CCD detector is processed by fast electronics near the detector head (known as the 'Blue Processing Electronics', or BPE) to extract information which is then transmitted to the data processing unit (DPU) in the digital electronics module (DEM).

After and event is located to a CCD pixel in the BPE, it is centroided using an algorithm resulting in two numbers 'm' and 'n'. Their division yields a number between -0.5 and +0.5 which is the position within the CCD pixel of the centre of the event (this is done independently in X and Y). This range is divided up into 8 sections or bins which are known as sub-pixels. This division and sorting into bins is performed by a lookup table RAM whose input are the 8 bit numbers m and n and which gives a 3 bit output of the sub-pixel number for the event.

Within the blue detector processing electronics there are circuit blocks designed to search for events in the frames of CCD data and to find values of event height, event energy, and the values of m and n in both X and Y. In normal operation the link to the DPU (Digital Processing Unit) uses a 24 bit wide FIFO in the processing electronic to buffer event address/ window ID information, which is then serialized, input to the DPU and reorganized into an address within its memory space and that location incremented. The processing electronics has a 4 way multiplexer to select the various resolution and windowing options. The ICU (Instrumental Control Unit) selects the appropriate mode with the multiplexer - standard data acquisition mode, event characteristics mode, or a centroiding information mode. During data acquisition, the hardware event valid signals is used to store the formatted event address in the FIFO.