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The CMS Pixel FED
Veröffentlicht am 08.10.2007 in TWEPP07 Proceedings

The innermost detector of the CMS Experiment consists of 66 million silicon pixels. The hit data has to be read out and must be digitized, synchronized, formatted and transferred over the S-Link to the CMS DAQ. The amount of data can only be handled because the readout chip (ROC) delivers zero-suppressed data above an adjustable threshold for every pixel.

The Pixel FED 9U VME module receives an analog optical signal representing the encoded information from the pixel detector. Each 25 ns slice of the analog is re-digitized and processed. For instance, the position of a hit pixel on a module is transmitted with five symbols coded in six pulse height steps each. The data of 36 inputs build a final event data block. The data block from each detector module with either 16 or 24 ROCs differs in length and arrival time.

Depending on the data length and trigger rate, there can be a skew of several events between any two inputs. That is possible because the ROC has a multi-event time stamp memory and the readout bandwidth is limited.

The information processed by the Pixel FED will be transferred over the S-Link to the CMS DAQ. Each module must be able to process a trigger rate of 100 kHz or, if in trouble, to send an alarm signal. The number of inputs is limited by the maximum data transmission rate of the S-Link (640 MB/s) for the expected high luminosity of LHC.

The data flow on the module is continuously controlled. Errors are written in an error memory, included in the data stream and if critical sent to the general CMS readout control.


Autoren: Manfred Pernicka, Siegfried Schmid, Helmut Steininger

weitere Autoren: D. Kotlinski, W. Johns

Download: twepp07_pixelfed.pdf
Kategorie: Nicht- reviewtes Paper