  The small-strip Thin Gap Chamber (sTGC) will be used for both triggering and
precision tracking purposes in the upgrade of the ATLAS forward muon
spectrometer. Both sTGC pad and strip detectors are readout by a Trigger Data
Serializer (TDS) ASIC in the trigger path. This ASIC has two operation modes to
prepare trigger data from pad and strip detectors respectively. The pad mode
(pad-TDS) collects the firing status for up to 104 pads from one detector layer
and transmits the data at 4.8 Gbps to the pad trigger extractor every 25 ns.
The pad trigger extractor collects pad-TDS data from eight detector layers and
defines a region of interest along the path of a muon candidate. In the strip
mode (strip-TDS), the deposited charges from up to 128 strips are buffered,
time-stamped, and a trigger matching procedure is performed to read out strips
underneath the region of interest. The strip-TDS output is also transmitted at
4.8 Gbps to the following FPGA processing circuits. Details about the ASIC
design and test results are presented in this paper.
