Patent ID: 7535441

Claim:
A display driver for a passive organic electroluminescent display, the display driver comprising: a controllable current generator to provide a variable current drive output to the display, the current generator comprising at least one bipolar transistor in series with the current drive output; and control circuitry to control the current generator by a current input, whereby the display brightness is adjustable by controlling the current generator to vary the current drive to the display, wherein the at least one bipolar transistor has an emitter terminal directly connected to a power supply line of the driver, the control circuitry comprises a plurality of current sources to provide a variable current output to the current generator current input, and a first said current source is arranged to be controlled to source a predetermined current and each of said current sources except said first current source is arranged to be controlled to source a predetermined current that is greater than the predetermined current of the next lowest predetermined current of said current sources.