Systems for measuring the angle of incident light are required for many applications in vehicles. Certainly the most important and well known among them is the control of air-conditioning systems mentioned here. For this application, sensors are placed e.g. on top of the dashboard behind the windshield to detect the energy and the angle of incident sunlight for an optimized control of air conditioning.
Fig. 1: Sensor principle for different angles of incidence
Conventional sensor systems for the measurement of the angle of incident light use two (or more) sensors, placed at a certain angle towards each other and thus determine the angle of insolation on the basis of several signals. The previously required three-dimensional setup is unsatisfying, though. While it represents a source of mostly optical irritation on the dashboard, it can be accommodated in the mirror base only with great difficulty due to the most limited available space.
The new sensor made by ELMOS has a planar setup, requires no optics, and can be integrated in one CMOS process together with read-out circuit and additional electronics. If this sensor is placed sufficiently close to the dashboard surface, a planar transition between sensor and automotive environment is possible for the first time. The light reaches the surface of the sensor directly, without optical focusing or other manipulations. The sensor is assembled in a package of only 4x4 square millimeters. The sensor principle is based on measuring the difference of the photocurrent of two adjacent photo diodes. A shadow mask placed on top of the diodes adequately covers these photo diodes or leaves them exposed. As shadow mask, one of the metallization levels resulting from the IC manufacturing process is utilized.
By using a large number of diode pairs with a specially adjusted shadow mask, by principle any degree of measurement subtlety of the angle of incident light is made possible. The angle sensor presented here uses 64 diode pairs each in x and y-direction. By the sensor's very modest space requirements and its planarity, it is absolutely possible to install it e.g. in the vehicle's mirror base.
Functional principle and technical data
The angle sensor consists of a large number of diode pairs partially covered by a shadow mask. The IC contains two angle sensors in x and y-direction for the collection of the measuring data as well as two photo diodes of different spectral sensitivity for the measurement of radiation intensity. The maxima of spectral sensitivity are 550nm and 650nm. The latter value is of interest particularly for the control of air-conditioning systems. The visible blue spectral component of light, on the other hand, is required e.g. for the automatic switch-on of the dimmed headlights.