Speed- and sensitivity-enhanced integrated optical sensor with divided photodiode

Generally, a high-speed optical sensor consists of a photodiode and a transimpedance amplifier. If a large photosensitive area is demanded, the resulting large junction capacitance of the photodiode limits both the bandwidth and the noise behavior of the transimpedance amplifier. Therefore we suggest an innovative approach, which divides the photodiode into four electrically isolated sections. Each of the four-quarter photodiodes is connected to a transimpedance amplifier and their output voltages are combined with a summation amplifier. The capacitance of each of the four-quarter photodiodes is only one fourth of the capacitance of the undivided photodiode, therefore the bandwidth of the innovative optical sensor is 223MHz, which is three times as high as the bandwidth of a transimpedance amplifier with an undivided photodiode. The photo-sensitivity is more than doubled to 75mV/μW.