Signal Shapes

In the forward endcap EMC the signals coming from Hamamatsu Vacuum Photo Tetrodes (VPTTs) as well as from Hamamatsu Large Area Avalanche Photodiodes (LAAPDs) are first fed to integrating Low Noise Preamplifiers (LNP) inside the cold volume of the detector. The output signals of the preamplifiers are routed out of the cold volume and fed into FPGA-driven digitizing boards which contain a shaping amplifier at their input stage. The following measurements have been taken using a VPTT (and an LAAPD respectively) which is mounted inside the Proto192. The Lightpulser was used to periodically illuminate the PWO crystal sitting in front of the VPTT (APD) with light pulses similar to the scintillation light of PWO.

The amplitude of the preamplifier output signal has been measured with an oscilloscope (terminated with 50 Ohms), the results are given in the pictures below (black text in HIGH gain part of the picture). The pictures below show the signal shape as seen by the digitizing board and have been acquired directly from the FPGA on the ADC board using Xilinx' ChipScope. The ADC board that was used (ADC32DR v1.0) is a prototype for the board that will be used in the forward endcap. The input signal (U.FL differential input) is first shaped, then split into two different gain branches, namely a x1 (LOW Gain) and a x16 (HIGH Gain) signal. Please note, that although the board is designed for a differential input signal the LNPs deliver a single ended signal, thus only half the conversion rage of the ADCs can be used. The pictures show the conversions of the LOW as well as the HIGH gain branch after digitization for different signal amplitudes and detector types.

Although the digitizing boards as well as other components are still under development these measurements show actual waveforms coming from a running detector and can be used e.g. for simulations.

For further use you can find the raw data of these waveforms (High and Low gain) in a machine-readable ASCII format here:

• x3y3-2-1000V_sig7comma7mV_1.prn: VPTT at 1000V; Signal: 7.7mV behind Preamp

• x3y3-2-1000V_sig770mV_1.prn: VPTT at 1000V; Signal: 770mV behind Preamp

• x4y2-2-360V_sig6comma15mV_1.prn: APD at 360V; Signal: 6.15mV behind Preamp

• x4y2-2-360V_sig615mV_1.prn: APD at 360V; Signal: 615mV behind Preamp

-- MalteAlbrecht - 25 Oct 2013