Monolithically Integrated GaN Photodetector and Bootstrapping Transimpedance Amplifier

Monolithic integration of photodetector and transimpedance amplifier is demonstrated for galvanically isolated control of GaN power switches. The transimpedance amplifier includes a bootstrapping comparator and an optical receiver stage. The bootstrapping comparator features depletion-mode AlGaN/GaN high electron mobility transistors for optimized speed and input common mode range spanning from -1 to 8 V. The comparator delivers a voltage gain up to 176 V/V and a unity-gain bandwidth of 3.58 MHz. Within the optical receiver stage, the photodetector exhibits a photocurrent range of 50 to 100 nA when stimulated by a 340 nm wavelength light emitting diode. Together with a 330 kΩ pull-up resistor, the optical receiver stage generates a voltage signal ranging from 16.5 to 33 mV. The signal is then amplified by the bootstrapping comparator, resulting in an output voltage signal with a peak-to-peak voltage of 3.1 V, operating at 1 kHz frequency.