  In the readout electronics of the Water Cerenkov Detector Array (WCDA) in the
Large High Altitude Air Shower Observatory (LHAASO) experiment, both
high-resolution charge and time measurement are required over a dynamic range
from 1 photoelectron (P.E.) to 4000 P.E. The Analog Front-end (AFE) circuit is
one of the crucial parts in the whole readout electronics. We designed and
optimized a prototype of the AFE through parameter calculation and circuit
simulation, and conducted initial electronics tests on this prototype to
evaluate its performance. Test results indicate that the charge resolution is
better than 1% @ 4000 P.E. and remains better than 10% @ 1 P.E., and the time
resolution is better than 0.5 ns RMS, which is better than application
requirement.
