  The Large High Altitude Air Shower Observatory is in the R&D phase, in which
the Water Cherenkov Detector Array is an important part. The signals of
Photo-Multiplier Tubes would vary from single photo electron to 4000 photo
electrons, and both high precision charge and time measurement is required. To
simplify the signal processing chain, the charge-to-time conversion method is
employed. A prototype of the front-end readout ASIC is designed and fabricated
in Chartered 0.35 {\mu}m CMOS technology, which integrates time disctrimination
and converts the input charge information to pulse widths. With Time-to-Digital
Converters, both time and charge can be digitized at the same time. We have
conducted initial tests on this chip, and the results indicate that a time
resolution better than 0.5 ns is achieved over the full dynamic range (1~ 4000
photo electrons, corresponding to 0.75 ~ 3000 pC with the threshold of 0.188
pC); the charge resolution is better than 1% with large input amplitudes (500 ~
4000 photo electrons), and remains better than 15% with a 1 photo electron
input amplitude, which is beyond the application requirement.
