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for Visible Light
| Highly sensitive photo
transistors for visible light now are available in the high voltage
process Smart-BCD developed by PREMA Semiconductor. No additional
process layers are necessary for these transistors that can,
moderately priced, be integrated into mixed-signal ASICs. The photo transistors LS21 and LS31 offer a spectral sensitivity with a maximum in the visible range at about 610 nm. The LS21 is based on a super beta transistor with high gain that enables a high sensitivity even for weakest light signals. The spectral sensitivity at 610 nm is about 540 A/W, the LS31 based on a standard transistor offers a sensitivity of 70 A/W. Both photo transistors are very linear over a wide illumination range. 
Data
Sheet Photo Transistor
PDF
The light sensor SE15L consists of four super beta phototransistors LS21 combined to a differential stage. The transistors are placed in a quad split order to optimize the matching properties. Two transistors arranged in a diagonal are covered with metal. This differential stage amplifies the light current minus the dark current. An illuminance smaller than 1 Lux can be detected with the SE15L even at a chip temperature of 120°C. An ASIC has the advantage of optimizing the transistor matching whereas such a compensation of the dark current is difficult to achieve with discrete components. The photo transistors can be produced cost-effectively with the Smart-BCD process for custom specific analog ICs. The low number of defects even for a large light sensitive area guarantees a high wafer yield. A high sensitivity can be reached even with small sizes by using high gain super beta transistors. This combination of highly sensitive photo transistors and analog / digital analysing circuits offers a high grade of system integration and is well suited for a wide range of applications such as consumer electronics or automotive applications. |