  Using Commercial Off-The-Shelf (COTS) Operational Amplifiers (OpAmps) and
Complementary Metal-Oxide Semiconductor (CMOS) transistors, we present a
demonstration of the Q-Pix front-end architecture, a novel readout solution for
kiloton-scale Liquid Argon Time Projection Chamber (LArTPC) detectors. The
Q-Pix scheme employs a Charge-Integrate/Reset process based on the Least Action
principle, enabling pixel-scale self-triggering charge collection and
processing, minimizing energy consumption, and maximizing data compression. We
examine the architecture's sensitivity, linearity, noise, and other features at
the circuit board level and draw comparisons to SPICE simulations. Furthermore,
we highlight the resemblance between the Q-Pix front-end and Sigma-Delta
modulator, emphasizing that digital data processing techniques for Sigma-Delta
can be directly applied to Q-Pix, resulting in enhanced signal-to-noise
performance. These insights will inform the development of Q-Pix front-end
designs in integrated circuits (IC) and guide data collection and processing
for future large-scale LArTPC detectors in neutrino physics and other
high-energy physics experiments.
