Variable-gamma circuit for colour television based on the MOS voltage-translinear principle

Abstract

In this paper a variable-gamma system is discussed for application in high-quality colour television receivers. A variable-gamma system can significantly improve the quality of the video image by enhancing the contrast in darker parts of the image without degrading the lighter areas of the screen. The adjustment of gamma can replace the traditional contrast and intensity adjustments. The main part of the variable-gamma system is a nonlinear function block, which is implemented by an MOS translinear (MTL) circuit. This circuit was realized in a standard 2.5 μm CMOS process. The circuit operates at a single 5V supply voltage. The measured small-signal-3dB bandwidth is 20MHz. The circuit response is insensitive to temperature, which is an important property of translinear circuits.