Contrast controllable electrochromic display driver circuit

Driver circuit means for an electrochromic display capable of producing uniform display contrast thereon, said electrochromic display including a counter electrode and a plurality of segment electrodes of various sizes, comprising:

• constant current means connected to said counter electrode for providing a constant current in response to a write signal applied thereto;
• a plurality of switching means connected, respectively, to said plurality of segment electrodes, each of said switching means having a gate means and switching to a conducting state in response to respective constant voltage switching signals applied to said gate means to control the flow of said constant current into corresponding ones of said segment electrodes;
• means providing write command signals corresponding one to each of said switching means and having first and second control states;
• control circuit means connected to said plurality of switching means for selectively generating a like plurality of constant voltage switching signals, said control circuit means including:
• constant voltage means for providing a constant voltage signal;
• and
• a plurality of gate controlling circuit means interconnecting said constant voltage means and respective ones of said gate means of said plurality of switching means and responsive to said constant voltage signal and respective ones of said write command signals in the first said control state for generating said plurality of constant voltage switching signals in response thereto, said switching signals switching respective ones of said switching means to said conducting state and maintaining said conducting states for respective durations sufficient to apply said constant current to said segment electrodes for coloring said segment electrodes by a uniform application of charge per unit electrode size.