Systems and methods for a front-end circuit receiving a current from a photodiode receiving a signal light and ambient light have been disclosed. In a preferred embodiment the front-end circuit accommodates a photo diode current, generated by a signal light from an infrared LED diode in presence of a current generated by ambient light for a rain-sensing system. The circuit invented has a high dynamic range comprising a programmable transresistance amplifier, a switched capacitor programmable gain amplifier and a switched capacitor fourth-order oversampled sigma-delta A/D converter including an optimized digital filter. Furthermore coarse and fine IDACs are used to successively subtract a current generated by ambient light.