Patent ID: 6476591
Filing Date: 2002-11-05
Classification: G09G

Abstract:
A power supply device for driving liquid crystal that generates N numbers of liquid crystal drive voltages between first and second reference voltages, the power supply device comprising:a voltage division circuit that divides a voltage between the first and second reference voltages to generate N pairs of first and second voltages including N numbers of first voltages each of which is equal to or higher than each of the N numbers of liquid crystal drive voltages, and N numbers of second voltages each of which is equal to or lower than each of the N numbers of liquid crystal drive voltages, when the first voltage is not equal to the second voltage in each pair; and N numbers of impedance conversion circuits that generate N numbers of impedance converted liquid crystal drive voltages based on the N pairs of the first and second voltages; wherein each of the N numbers of impedance conversion circuits comprises: a voltage follower type of differential amplification circuit to which a pair of first and second voltages among the N pairs of first and second voltages is input and which generates a first output voltage based on the first input voltage and further generates a second output voltage based on the second input voltage; and an output circuit including a P-type transistor and N-type transistor connected in series between a first power supply line for the first reference voltage and a second power supply line for the second reference voltage, and having an output terminal which is connected between the P-type transistor and N-type transistor and outputs one of the N numbers of liquid crystal drive voltages; and wherein the N-type transistor is turned on when an output voltage of the output terminal is higher than the first voltage, the p-type transistor is turned on when an output voltage of the output terminal is lower than the second voltage, and both the p-type and N-type transistors are turned off when an output voltage of the output terminal is between the first and second voltages.