Differential amplifier, method for inverting output polarity of the same, and source driver

Abstract

A differential amplifier includes: an output amplifier circuit; a bias circuit; and a pulse applying circuit. The output amplifier circuit receives a positive gradation voltage and a negative gradation voltage alternately by an input stage circuit and supplies a drive voltage generated based on the gradation voltage to a display panel. The bias circuit generates a bias voltage in synchronization with a strobe signal which is a trigger for a polarity inverting operation of the gradation voltage and applies the bias voltage to a constant current source controlling a current of the input stage circuit. The pulse applying circuit generates a pulse voltage having a voltage level higher than a voltage level of the bias voltage and couples the pulse voltage to the bias voltage.

1 . A source driver for use with a display panel, the source driver comprising:
 a differential amplifier including:
 an input circuit configured to provide a positive gradation voltage and a negative gradation voltage alternately, and 
 an output amplifier circuit configured to receive the positive gradation voltage and the negative gradation voltage alternately by the input circuit and supply a drive voltage generated based on the gradation voltage to the display panel; 
   a bias circuit configured to generate a bias voltage in synchronization with a strobe signal which is a trigger for a polarity inverting operation of the gradation voltage and apply the bias voltage to a current source controlling a current of the input circuit; and   a pulse applying circuit configured to generate a pulse voltage having a voltage level higher than a voltage level of the bias voltage and couple the pulse voltage to the bias voltage.   
     
     
         2 . A source driver according to  claim 1 ,
 wherein the input circuit includes:   a N-channel MOS transistor as a first current source included in the current source,   wherein the pulse applying circuit generates the pulse voltage having a waveform with a rising time longer than a falling time and couples the pulse voltage to the bias voltage to be applied to the N-channel MOS transistor.   
     
     
         3 . A source driver according to  claim 1 ,
 wherein the input circuit includes:
 a P-channel MOS transistor as a second current source included in the current source, 
   wherein the pulse applying circuit generates the pulse voltage having a waveform with a falling time longer than a rising time and couples the pulse voltage to the bias voltage to be applied to the P-channel MOS transistor.   
     
     
         4 . A source driver according to  claim 1 ,
 wherein a pulse width of the pulse voltage is equal to or more than a pulse width of the strobe signal.   
     
     
         5 . A source driver according to  claim 1 ,
 wherein the pulse voltage has a voltage level which is level-shifted to a voltage level of a positive power source for the differential amplifier.   
     
     
         6 . A source driver according to  claim 1 ,
 wherein the pulse applying circuit includes:
 a pulse generating circuit configured to generate the pulse voltage in synchronization with the strobe signal, and 
 a coupling capacitance configured to couple the pulse voltage to the bias voltage. 
   
     
     
         7 . The source driver according to  claim 6 ,
 wherein the coupling capacitance includes a parasitic capacitance of a line to which the pulse voltage is applied.