The present disclosure describes an ultraviolet (UV) sensor configured to detect a target UV spectrum (e.g., UVB spectrum). The UV sensor includes a first photodiode with a first UV spectral response and a second photodiode with a second UV spectral response. A filter layer having a graded spectral response is formed over the second photodiode, and the second UV spectral response is affected by a controlled parameter (e.g., thickness) of the filter layer. The UV sensor further includes a subtraction circuit coupled with the first photodiode and the second photodiode. The subtraction circuit is configured to provide a differential response based on a difference between the first UV spectral response and the second UV spectral response. The controlled parameter of the filter layer can be selected such that the differential response provides a detected spectral response of the target spectrum.