CDF COT - ASDQ Overview

The front-end electronics for the COT begin with Amplifier-Shaper-Discriminator-dE/dx (ASDQ) boards mounted on the endplate which process the analog signals and send them to TDC's via a micro-coax/repeater/flat-cable chain.

After input protection and amplification, the analog pulse is shaped by cancelling the ion tail, which improves high rate operation. A baseline restoration is then performed, which returns the signal to zero to prevent large signals from shifting the threshold point. The signal is then discriminated, and the measurement of charge above threshold is encoded into the width of the output pulse.

The 8-channel ASDQ ASIC chip inputs control voltages to set the threshold and output width, has an optional factor of 2 attenuator, and can deactivate dE/dx for high rates. The chip also accepts a calibration pulse from the TDC which injects a variable amount of charge directly into the preamp.

Three 8-channel ASDQ chips are housed on 24-channel ASDQ daughter boards, which supply +/- 3V power and control voltages. The daughter boards contain a single-row header for connection to ASDQ motherboards, processing signals from two COT supercells. A double-row output header then connects to the micro-coax to send the discriminated and width-encoded signals to the TDC's.

The ASDQ daughter boards are mounted onto the endplate motherboards, and clamped to the extrusions via control voltage (CV) and ground (CG) boards running the circumference of the superlayer. The CV boards provide supply and control voltages to the daughter boards through short, 10-line ribbon cables.

The ASDQ power is input to copper bus bars on the CV boards from the LV filter box containing Vicor +/- 3V supplies with associated filtering and trimming circuitry. The control voltages originate from VME-based VMIC-4132 DAC modules located in the TDC crates. To accommodate the current requirements of the ASDQ's, these DAC voltages are driven by bufferboards mounted on the endplate, which in turn receive power from +/- 5V Condor supplies located in the LV filter box.