Abstract: Based on the detailed analysis of the loading properties of a medium or small size TFT-LCD driver IC,a novel output buffer circuit of driving voltages is proposed.By using negative voltage feedback,the operating states of the output stage in the output buffer circuit can be controlled dynamically,which can provide source current and sink current alternately,so that the output voltage fluctuations can be rejected effectively.Compared with a conventional push-pull output buffer circuit,it has such advantages as lower static power consumption,smaller chip area,and better stability.Two output buffer circuits driving different voltages are designed and implemented using a 0.25μm CMOS process.HSPICE simulation results show that the static current is 3μA and the offset voltage is less than ±2mV.Furthermore,when the driving voltage for the TFT-LCD panel is switched between -8 and 16V,the fluctuations and the recovering times of the output voltages are less than ±0.4V and 7μs,respectively.By measuring the TFT-LCD driver IC’s engineering samples,it is shown that the proposed output buffer circuits can completely satisfy the demands of a medium or small size TFT-LCD driver IC.

Key words: TFT-LCD driver IC, output buffer circuit, negative voltage feedback, source current and sink current