This　paper　proposes　a　neural　stimulation　integrated　circuit　design　with　multiple　current　output　modes.　In　the　cathodic　stimulation　phase　and　anodic　stimulation　phase,　each　output　current　waveform　can　be　independently　selected　to　either　exponential　waveform　or　square　wave,　so　the　stimulator　holds　four　stimulation　modes.　To　minimize　the　headroom　voltage　of　the　output　stage　and　enhance　the　power　efficiency　of　the　proposed　stimulator,　we　introduce　the　exponentially　decaying　current　which　is　realized　by　the　exponential　current　generation　circuit　in　this　work.　It　can　enhance　the　longer　duration　of　the　stimulation　pulse　as　well.　In　case　the　residual　charge　may　cause　harm　to　patients,　a　charge　balancing　technique　is　implemented　in　this　work　for　all　operation　modes.　The　four-channel　stimulator　IC　is　implemented　in　a　180-nm　CMOS　process,　occupying　a　core　area　of　1.93　mm2.　The　measurement　results　show　that　the　proposed　stimulator　realized　a　maximum　power　efficiency　of　91.3%　and　the　maximum　stimulation　duration　is　3　times　larger　than　previous　works.　Moreover,　even　in　exponential　output　waveform　mode,　the　maximum　residual　charge　in　a　single　cycle　is　only　255　pC　due　to　the　proposed　charge　balancing　technique.　The　experiment　results　based　on　the　PBS　solution　also　show　that　the　stimulator　IC　can　remove　residual　charges　within　60　μs,　and　the　electrode　voltage　remains　stable　within　a　safe　range　under　multicycle　stimulation.　IEEE