LTPS AMOLED显示器像素电路阈值电压补偿效果的改善

Improvement of threshold voltage compensation of LTPS AMOLED pixel circuit

为改善LTPS AMOLED显示器像素电路阈值电压变动性补偿效果,本文分析了相关电压型像素电路的工作过程,确认了影响阈值电压补偿效果的关键因素,包括显示信号刷新扫描行周期对阈值电压获取充电时间的制约、驱动信号形成过程中相关TFT电容增量造成的阈值电压精度损失等。针对这些关键因素,本文提出了像素电路改进对策。通过分离阈值电压获取和数据电压信号刷新过程实现阈值电压获取充电时间的延长,通过反向增量电容补偿相关电容增量误差。在像素OLED驱动电流受阈值电压变动影响突出的低灰阶状态下,模拟结果表明阈值电压获取和数据电压信号刷新过程分离像素电路的OLED驱动电流变动性是参考电路的1/7;反向增量电容补偿像素电路OLED驱动电流变动性大约为无补偿参考电路的1/2。补偿效果样品视觉评价结果与模拟结果趋势相符。

The key factors affecting threshold voltage variation compensation are identified through analyzing the operation processes of a relevant voltage program LTPS AMOLED pixel circuit.The factors include charging time restriction on threshold voltage detecting process due to data voltage signal refreshing period,and accuracy loss of threshold voltage in voltage program caused by capacity increment of related TFTs.Circuit countermeasure to these adverse factors are put forward to extend the charging time through separating the threshold voltage detection from data voltage signal refreshing process,and to compensate the error due to capacity increment through a TFT with reversed capacity increment.In pixel circuit state simulation under a low grey level display state,the variation of OLED driving current of pixel circuit of separated threshold voltage detection and data voltage signal refreshing is less than a seventh current variation of the reference circuit,and the variation of OLED driving current with capacity increment compensation is about half the current variation of the pixel circuit without capacity increment compensation.The improving effects in samples demonstration are consistent with the trend of simulation results.