Patent ID: 7038402
Filing Date: 2006-05-02
Classification: H05B

Abstract:
1. A method to achieve linear and exponential control over a current to drive color LEDs is comprising: (1) provide a control unit for current digital-to-analog converters, a Digital Switches Control unit, at least one set of color LEDs, and a linear current digital-to-analog converter cascaded with an exponential current digital-to-analog converter; (2) activate a first color of color space of color LEDs by said Digital Switches Control unit; (3) define a floating-point number wherein its mantissa defines the color composition of the color LEDs and its exponent defines the brightness of the LEDs; (4) split said floating-point number into its mantissa and exponent; (5) convert said exponent to a current representing an analog signal of the exponent using said exponential current digital-to-analog converter; (6) convert said digital floating point number into an analog current by converting linearly said mantissa by said linear current digital-to-analog converter using the output current of the previous step as biasing reference current; (7) use the output current of said cascaded exponential and linear digital-to-analog converters as current sink for the currently assigned color of the color LEDs in order to achieve linear and exponential control over a current to drive said color LED; (8) go to step 2 if the currently assigned color is the last color of the color space used, otherwise go to step (9); and (9) activate next color of color LEDs by said digital switches unit and go to step (3).