The SCA is a storage device used to save analog readings from each calorimeter channel until they can be read by the ADC after an event has occurred.  It is essentially an analog time delay element which holds signals until they are either digitized or discarded.  The capacitor cells can be written to or read from in a sequential or random manner.  While the SCA chip is capable of reading out one channel while writing another, this significantly degrades the cell to cell uniformity and we will not use the SCA in this manner.

In operation a certain SCA cell depth is addressed and a voltage level is stored there.  This process would be continued in a circulating fashion, to provide a buffer of event information.  When interesting information is collected it can be read out and digitized by and ADC.

Orbit Semiconductor fabricated all the wafers we anticipated needing last year before shutting down their four inch line.  A total of 491 wafers were fabricated.   During initial testing we found that 45% of the units were good.  About halfway into testing, lower than expectance yields were occurring.  We are currently investigating the cause of this problem.

The SCAs area combination of digital and analog circuitry which makes testing somewhat challenging.  Tests that are done should verify that each individual cell is functional and addressed correctly, and that the voltage levels read back from a cell are within a window of tolerance of the value written.  Testing should check for cross-talk between adjacent cells or channels and excessive power consumption.   Testing should be quick.

An electronic SCA tester has been designed to perform a full functional test of the SCAs.  Since there are two package types, two different tester types are required.  The analog portion of the tester will provide inputs to the SCA with varying voltage levels.  Output levels must fall between a high and low tolerance of the input for the SCA to be passed as goof.  Chip power must also be within a certain tolerance level.  Input voltage levels are set by analog switches.  The digital portion of the tester coordinates all of the timing and controls necessary to perform the tests.

The test covers the low and high range of the device.  It test functionality of each cell, and checks for cross-connected cells and cells with addressing failures.   Both testers have been built and testing is more than halfway completed.