25 March 1996 Increasing the dynamic range of an array of light sensors using a new thin-film circuit
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Abstract
Previously realized circuits for solid state light sensitive arrays fabricated in thin-film technology show a comparatively small dynamic range. A wide dynamic range as well as a large sensitivity of the output signal to the change of the input signal (irradiance) is required. A circuit which satisfies these requirements is described. The circuit consists of two thin-film transistors (TFTs), a photoconductor, and a fixed resistor. The photoconductor is used to detect the incoming light whereas the first TFT generates the logarithm of the photocurrent in form of a voltage. The second TFT and the fixed resistor invert the signal of the first stage and determine the slope of the output signal. The sensor's characteristic can be shifted over a wide dynamic range by using an appropriate control voltage. The circuit is simulated by SPICE, employing a special model for the TFTs. The sensor's characteristics show a large dynamic range of 4 decades when shifted by means of the control voltage. At the same time it exhibits a high sensitivity of 1.8 V/W/m2 due to the steep slope of its characteristics. This circuit was then built in a-Si:H thin-film technology. The measured characteristics match very well the simulations.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Dietmar Horst, Holger Scherr, Ernst H. Lueder, "Increasing the dynamic range of an array of light sensors using a new thin-film circuit", Proc. SPIE 2654, Solid State Sensor Arrays and CCD Cameras, (25 March 1996); doi: 10.1117/12.236089; https://doi.org/10.1117/12.236089
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