Upgrade to the front-end electronics of the BESIII muon identification system

Resistive Plate Chambers （RPCs） built from a new type of Bakelite developed at Institute of High Energy Physics （IHEP）, Chinese Academy of Sciences have been used in the BESIII Muon identification system for several years without linseed oil coating, but characteristic aging performances were observed. To adapt to the RPCs in the aging state, the front-end electronics have been upgraded by enhancing the front-end protec- tion, improving the threshold setting circuit, and separating power supplies of the comparator and the field programmable gate array （FPGA）. Improvements in system stability, front-end protection and threshold consis- tency have been achieved. In this paper, the system upgrade and the test results are described in detail.