W. Dabrowski,
Faculty of Physics and Nuclear Techniques, Cracow, Poland
R. Szczygiel, M. Wolter,
Institute of Nuclear Physics, Cracow, Poland
A. Clark, D. Ferrere, D. La Marra, D. Macina, M.C. Morone, A. Zsenei,
University of Geneva, Switzerland
F. Anghinolfi. J. Kaplon, C. Lacasta, S. Roe, M. Turala P. Weilhammer,
CERN, Geneva, Switzerland
0. Dorholt, B. Sundal,
University of Oslo, Norway
Z. Dolezal, M. Hornung, C. Ketterer, J. Ludwig, G. Rieth, M. Rogalla, K. Runge,
University of Freiburg, Germany
T. Kohriki, T. Kondo, S. Terada, Y. Unno,
KEK, Japan
P. Kodys,
Charles University, Prague, The Czech Republic

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Electrical module prototypes with the geometries defined for the barrel cylinder and the forward disks of the Silicon Tracker in ATLAS have been tested. The barrel module consists of two daisychain 6cm long strips detector (80um pitch) with a readout hybrid placed near the center of the detector area. The forward module consists of two daisy-chain fan-shape geometry detectors with a readout hybrid placed at the end of the detector strips. Each hybrid is supporting six ABCD chips and the passive components for decoupling and detector biasing. Each chip provides the signal amplification, discrimination and Level I latency for 128 channels. The back-end is organized in such a way that one ABCD chip (configured as "Master") collects the data from six chips to be transmitted out of the module. The "Master" chip sends serialized data on a differential low level signal wire pair. Data is collected from the five neighbour chips by using a token and data pass circuitry. The full functionality of this system has been proved.

Analog performance of modules was evaluated by using the calibration circuitry internal to the front-end chips, first with no detectors connected, then by connecting 6cm long strips and finally 12 cm long strips. Gain and noise values obtained with no or short detectors are corresponding to the design goals. The dispersion of threshold is measured to be 4 to 5 times higher than the expected values from the design calculations. This problem has been traced back to the insufficient 
 matching properties of a resistive component in the DMELL process used for the fabrication of the ABCD chips. The evaluation of the module with 12 cm strips has shown marginal stability with the normal biasing conditions on the analog amplification chain. Several cumulated parasitic effects, which can provide feedback paths, are needed to trigger the unstable operation. Each one has been analyzed. A specific feedback path due to the SOI structure of the wafers used for the DMILL process has been identified. A proper grounding and detector biasing scheme has also shown a great importance. Some modules operate in stable conditions with 12 cm detector strips if the amplification gain is reduced by 40%. In the later condition, the input noise meets the design specification of 1400 el. with 12cm strips and detector bias lOOV. Gain and threshold dispersions are not affected. Solutions to limit the potential contributions to instability, and local threshold setting to reduce the threshold dispersion across channels have been implemented into the second version of the chip (ABCD2T).

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Electrical modules for the ATLAS Silicon Tracker (SCT) have been fabricated and tested. The modules consist of 6 ABCD front-end chips connected to silicon strip detectors, with the electronics hybrid and detector geometries specified for the barrel and forward part of the tracker. Tests were done with the second batch of the ABCD chip, connected to 6cm or 12cm long strip detectors. The functionality of the modules are demonstrated, including the token pass readout mechanism which allows the serial transmission of the data out of 768 strips on one differential pair only. Threshold scan, noise, gain and offset spread have been evaluated. The performance of modules depends on the signal gain in ABCD chips and on the quality of the grounding and detector biasing. Improvements adopted for the next module construction will be discussed.
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