A switched-capacitor PWM generator for LCD backlight brightness control

Abstract

Abstract:In this paper, a pulse width modulation (PWM) generator based on a switched capacitor for LCD backlight brightness control is described. The proposed scheme uses a simple RC network along with a clocked-comparator which samples the output of the ambient light sensor, and generates a PWM signal corresponding to the light level. Furthermore, by using a switched-capacitor resistor with variable clock frequency, the RC time constant is programmable and less sensitive to process variations with respect to passive resistors. In addition, it is shown that the linearity of the proposed PWM generator can be enhanced by replacing the RC network resistor with a constant current source. The operation of the PWM generator is verified through circuit level simulations, and the prototype circuit is fabricated using CMOS 0.18 um technology.