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Last modified: 7-OCT-1999


There is a very obvious crosstalk amongst the 16 channels associated with a given SAS/SCA chip pair; at about 1.5%, this is large compared to benchtop measurements of order 0.3%. The difference is not understood. However, the crosstalk appears to be larger on some 16-channel groups, than on others.

  1. Variation over sector
  2. Variation between chip channels
  3. Signal shape
  4. FEE charge injection crosstalk

Variation over sector

The apparent crosstalk within groups of 16 channels, as seen in the early TPC tests, was traced to a digitization problem by Chinh Vu and Spencer Klein. By varying component values on the board, one can trade-off between noise and "digital" crosstalk; the latter was reduced considerably at the expense of increasing noise from about 1.05 ADC counts to about 1.35 ADC counts.

Variation between chip channels

The crosstalk between various combination of channels within a group of 16 seems to vary considerably. This needs to be studied systematically and quantified.

Signal shape

Crosstalk signal appear to be partially differentiated version of the real signals; this needs to be systematically studied and quantified.

FEE charge injection crosstalk

The crosstalk from FEE charge injection seems to contain a larger differentiated component than does that from cosmic-ray signals. There also appears to be a signal induced by the on-board pulser. This needs to be systematically studied and quantified.