METHOD AND DEVICE FOR GENERATING BIAS VOLTAGE FOR DRIVING LIQUID CRYSTAL DISPLAY

PROBLEM TO BE SOLVED: To obtain a bias voltage generator making it unnecessary to loading many I/O ports by generating a control signal for controlling a bias current to a top level so as to output an LCD driving waveform from an LCD driver. SOLUTION: A system voltage monitor circuit 126 detects the current level of system voltage Vcc in response to a voltage detection request signal 127 outputted from a detection signal generation circuit 128 and generates a voltage level signal Vdet In response to the signal Vdet , a logic circuit 124 sends a control signal 125 to control the resistance of a resistor Rc to a regulated value in accordance with the current level of the system voltage Vcc . The equivalent resistance Rcq of a voltage division circuit 122 is changed in accordance with a change in the resistor Rc and bias voltage levels V. to V, which are sufficiently high levels for generating an LCD driving waveform from the LCD driver 110 are obtained. At the instant of switching the LCD driving waveform from one state to the other, a large bias current value is obtained by a resistor with 100 KΩ and capacitors C5 to C8.