Design Of A 16 Bit Constant Current Driver Application-special Chip For Large Color LED Display Screen

Just a few years, the Large color LED display which has bright color and broad angel, is becoming the mainstream product in high-definition flat panel display devices market, and will have more and more wide application. As a key component in big screen display system, the constant current LED driver IC, ensures the display evenness, meets demands for various application, so it attracted more and more attention.In this thesis, a 16-bit constant current LED driver IC with is designed. It supports 25MHz data shift frequency and realizes fast screen refresh with no flicker. The main innovations of this thesis are the usage of high precision reference voltage anti-offset technique, driving current output matching technique and the special design in both process parameters of doping concentration and chip layout. All of these ensure that in the condition that operating temperature changes from-40℃to 80℃, working voltage changes from 4.5V to 7V and load changes in broad width, the chip still meet constant current matching between channels and chips completely even when output currents of 16 channels up to 90mA.Firstly, the whole framework of the chip is built. Then, the band-gap reference module, constant current reference module, high precision current amplifier, over-temperature protection module, oscillator module and logic control module are designed. And the simulation results are given. Among them, chopping modulation is used in bandgap reference module to decrease offset voltage of operational amplifier, an improved current mirror is adopted in constant current reference module to enhance output impedance and current matching accuracy, an effective discharge circuit is adopted in high precision current amplifier to eliminate the clutter in output current, and ring oscillator composed of inverters is adopted in oscillator to reduce chip area. Finally, the simulation has been completed by using Cadence Hpsice software with the CSMC 5V 0.5uM process library, and all the important performance indexes have been analyzed and verified in detail. The simulation and testing results show that, the whole chip area is 1630μm×1230μm, the maximum output current of each channel achieves 106mA, adjusting rate of supply voltage is 0.3%, adjusting rate of output voltage(load) is 0.06%, output current error between channels is less than 2.1%, output current error between chips is less than 3.3%. Therefore, the designed chip has reached the technical index requirements.