Brown Bag Instrumentation Seminar

Yuan Mei, LBNL: "Charge waveform digitization by counting pulses and charge neutralization"

by Yuan Mei






For TPC charge waveform measurement, the Q-Pix concept (arXiv:1809.10213) offers a waveform digitization method by accumulating charge in a fixed-capacity bucket and recording the instances when the bucket becomes full.  The bucket is subsequently emptied (reset).  This results in a pulse series, where the inter-pulse time intervals encode the original charge waveform, enabling its reconstruction.  We demonstrate this scheme using commercial off-the-shelf components.  Rather than resetting the charge bucket, we inject fixed amounts of opposite charge to neutralize the accumulated charge, thereby converting the charge integrator into a Sigma-Delta modulator.  Our PCB-level implementation achieves a charge resolution of 2000 electrons, a bandwidth approaching MHz, and excellent linearity.  The circuit's architectural simplicity and its potential for integration into ASICs and larger systems will be discussed.