A monolithic integrated light-to-frequency chip was designed, and the chip test results were given. The photo current inside the photodiode varies with the intensity of light, and it will be converted to be voltage signal with the integrating capacitor. When the voltage reaches the threshold of the comparator, the comparator flips, the oscillator oscillates, and the light intensity will be converted into a frequency signal. Chips were fabricated with 0.6μm 2P3M process, and experimental results indicate that they can work normally under three-terminal packaging conditions with the chip size of 1.8mm×1.7mm, photodiode area of 850μm×850μm, nonlinearity of less than 1%, dark current of less than 1Hz, output signal duty cycle of 50%, and the maximum output frequency of 1MHz.
