Design Of Constant Current Driving Module For OLED Driver Chip

With the advancement of science and technology and the continuous developmentof electronic technology, a new type of flat panel display-organic light emitting diode(OLED) gradually has attracted people’s attention. OLED has a series of advantages,such as light weight, small thickness, a wide viewing angle, fast response, bright color.It has been widely used in vehicle-mounted display, mobile phone, instruments andapparatuses display and other display equipment. In order to meet various applicationrequirements, the research and design of new specific driver chips for OLED panelsbecome a research focus.This paper first introduces the basic structure of the organic light emitting devicesand its light-emitting principle and driving methods. Then give a brief overview ofdomestic research on OLED display that has been done and a couple of specific driverchips for OLED panels that appears on the market at present.The main work of this paper is to analyze and design one type of constant currentdriving circuit for a passive-matrix OLED driver chip. According to the designrequirements and overall architecture of the driver chip, divide the circuit into severalkey modules, including voltage reference module, contrast modulation module, constantcurrent reference generation and current mirror control module, pre-charging module.The band-gap reference in voltage reference module, adopts chopping modulationmethod to reduce the input offset voltage of the operational amplifier. Implemented intwo steps, contrast modulation module can achieve6-bits total of64levels contrastmodulation, of which its low5-bits is realized by switching programmable resistor andits MSB is individually controlled by other sub-circuit. Constant current referencegeneration module converts band-gap voltage divider to a current reference by thenegative feedback of operational amplifier and an external resistor. Adopted a highprecision current mirror structure, current mirror control module can improve the outputimpedance and current matching accuracy. Pre-charging module generates a currentpulse to quickly charge the parasitic cap of the circuit nodes when row scanning signalis valid, so that the OLED can emit light rapidly and does not affect its display effect.Based on the CSMC0.5μm mixing process model, using Spectre simulator inCadence platform, each module circuit is simulated, and some critical results andwaveforms of simulation are presented in this paper. And on this basis, some importantperformance index of each module circuit is analyzed and verified.