Differential Color Sensor Without Filters

Abstract

A semiconductor color sensor implemented without the use of color filters. Fabricating photodiodes using different semiconductor materials provide photodiodes with different sensitivities vs. wavelengths. A first embodiment uses photodiodes with different junction depths. A shallow junction depth produces a photodiode with its sensitivity peak in shorter wavelengths, while a deeper junction depth produces a photodiode with its sensitivity peak in longer wavelengths. Amorphous as well as crystalline structures may be used. A second embodiment uses photodiodes with different materials, such as Silicon-Germanium (SiGe) which has a longer wavelength peak sensitivity, and Silicon (Si) which has a shorter wavelength peak sensitivity in comparison. More than two photodiodes having different wavelength sensitivities may be used. Sensing current ratios between pairs of diodes allows color balance to be maintained.

1 - 6 . (canceled)  
   
   
       7 . A method of sensing the color of incident light comprising: 
 capturing a portion of the incident light with a first semiconductor photodiode of a first material comprising silicon with a sensitivity peak at a first wavelength and generating a first photocurrent;    capturing a portion of the incident light with a second semiconductor photodiode of a second material comprising silicon-germanium with a sensitivity peak at a second wavelength and generating a second photocurrent; and    computing the ratio of the first photocurrent to the second photocurrent.    
   
   
       8 . The method of  claim 7 , where the step of computing the ratio of the first photocurrent to the second photocurrent further comprises: 
 converting the first photocurrent to a first voltage representative of the first photocurrent,    converting the second photocurrent to a second voltage representative of the second photocurrent, and    computing the ratio of the first and second voltages.    
   
   
       9 . The method of  claim 7 , where the ratio is computed in analog form.  
   
   
       10 . The method of  claim 8 , where the ratio is computed in analog form.  
   
   
       11 . The method of  claim 7 , where the step of computing the ratio of the first photocurrent to the second photocurrent further comprises; 
 converting the first photocurrent to a first digital representation of the first photocurrent,    converting the second photocurrent to a second digital representation of the second photocurrent, and    computing the ratio of the first and second digital representations.