Differential color sensor without filters
View Patent ↗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. An improved color sensor, comprising:
a first semiconductor photodiode of a first material comprising silicon with a sensitivity peak at a first wavelength;
a second semiconductor photodiode of a second material comprising silicon-germanium with a sensitivity peak at a second wavelength;
a first amplifier associated with the first semiconductor photodiode and configured to develop a first voltage signal based on a photocurrent of the first semiconductor photodiode;
a second amplifier associated with the second semiconductor photodiode and configured to develop a second voltage signal based on a photocurrent of the second semiconductor photodiode; and
a circuit configured to develop a ratio between the first voltage signal and the second voltage signal, the ratio representative of the outputs of the first semiconductor photodiode and the second semiconductor photodiode.
2. The improved color sensor of claim 1 where the first and second photodiodes are combined in the same package.
3. The improved color sensor of claim 1 where the first and second photodiodes are fabricated on the same die.
4. The improved color sensor of claim 1 where the first and second photodiodes have different junction depths.
5. The improved color sensor of claim 1 where the first photodiode is an amorphous diode.