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Description
Summary
The front-end electronics of the Silicon Drift Detectors (SDDs) of ALICE is based on
two custom integrated circuits: PASCAL (Preamplifier Analog Storage and Conversion
from Analog to digitaL) and AMBRA (A Multievent Buffer Readout Architecture). PASCAL
is a mixed-mode integrated circuit that samples the signals coming from the detector
and digitizes them when a trigger signal is received. AMBRA is basically a RAM that
allows the derandomization of the trigger. This chip performs also some digital
signal pre-processing, like baseline equalization and 10-to-8bit compression. Both
ASICs have been designed and produced in 0.25 um CMOS technology. For cost reasons
the two chips have been fabricated using the same set of masks. Each 8-inch wafer
hosts 146 PASCAL and 146 AMBRA. This paper describes the test system developed for
the on-wafer testing and discusses the results obtained.
The test system is based on a Cascade Microtech Rel-6100 probe station with a
motorized chuck stage controlled via GPIB interface. It is required to use two
different full custom active probe cards for the two ASICs. Each probe card contains
custom to standard differential digital buffers.
To reduce as much as possible hardware dependence, the digital control signals are
generated by a data pattern generator (Agilent 16702B Logic Analysis System); the
outputs are read out by the logic state analyzer (on the same instrument) and then
sent to a PC for data analysis. For AMBRA, which is a pure digital IC, it is
possible to implement data analysis directly on the logic state analyzer. The data
produced by PASCAL are digitized analog signals and a more complex statistical
analysis isrequired for an adequate assessment of the performance. In this case the
raw data are sent to a PC. The computer performs online a complete data analysis
evaluating the critical parameters (gain, linearity, number of dead channels, ADC
and DAC performance, etc.).
The whole test system is controlled by a PC running a software developed in LabView.
The program allows to drive the test hardware (probe station and power supplies via
GPIB, data pattern generator and logic state analyzer via TCP/IP and all support
electronics), to control all test steps and to create report files for the database
in a friendly windows-based user interface.
The mass production testing system is installed at the INFN in Rome. The typical
testing time is 8 minutes for PASCAL and 5 minutes for AMBRA. The architecture of
the test system, the test selection criteria and the test results will be discussed
in detail in the final paper.
