Patent ID: 6225992
Filing Date: 2001-05-01
Classification: G05F,G09G

Abstract:
A bias-voltage generating apparatus for generating a set of bias voltages for an LCD driver to drive an LCD panel, comprising:a voltage divider including a plurality of resistors and at least one digitally-variable resistor for dividing a system voltage into a number of apportioned voltages serving as the bias voltages, said plurality of resistors and said digitally-variable resistor being connected in series to form a DC path through which a bias current flows;a system-voltage monitoring circuit for monitoring the system voltage to thereby generate a voltage-level signal indicative of the current level of the system voltage: anda logic circuit, in response to the voltage-level signal, for generating a contorl signal which adjusts the resistance of said digitally-variable resistor so as to adjust the bias current to a top level to allow the LCD driver to output a plurality of LCD wave-forms to drive the LCD panel,wherein said system-voltage monitoring circuit includes:a reference-voltage generator for generating a reference voltage;a plurality of voltage dividers, coupled to the system voltage, for generating a plurality of apportioned levels of the system voltage;a plurality of switches connecting the plurality of apportioned levels of the system voltage to a common signal line;a comparator having a negative input connected to receive the reference voltage and a positive input connected to the common signal line, said comparator generating a series of comparison signals indicative of a specified voltage range within which the current level of the system voltage lies; anda control circuit, coupled to said comparator and said plurality of switches, for selectively turning on said switches so as to allow said comparator to generate the comparison signals, said control circuit subsequently processing the comparison signals to thereby generate a voltage-level signal indicative of the range within which the current level of the system voltage lies.