  To better understand the energy response of the Antineutrino Detector (AD),
the Daya Bay Reactor Neutrino Experiment installed a full Flash ADC readout
system on one AD that allowed for simultaneous data taking with the current
readout system. This paper presents the design, data acquisition, and
simulation of the Flash ADC system, and focuses on the PMT waveform
reconstruction algorithms. For liquid scintillator calorimetry, the most
critical requirement to waveform reconstruction is linearity. Several common
reconstruction methods were tested but the linearity performance was not
satisfactory. A new method based on the deconvolution technique was developed
with 1% residual non-linearity, which fulfills the requirement. The performance
was validated with both data and Monte Carlo (MC) simulations, and 1%
consistency between them has been achieved.
