Source driver in liquid crystal display device, output buffer included in the source driver, and method of operating the output buffer

An output buffer included in a source driver of an LCD (liquid crystal display) device, the output buffer comprising:

• a differential input unit generating first control currents by amplifying the difference between voltages of an analog image signal and a signal output from the output buffer;
• a gain unit generating second control currents by adding the first control currents together;
• and
• an output unit outputting a signal obtained by amplifying the analog image signal in response to the second control currents,
• wherein the differential input unit comprises
• first and second bias current sources having a first amount of current during a charge recycling period in which a source line of the LCD device is precharged to a precharge voltage, and
• third and fourth bias current sources having a second amount of current during a driving period in which the amplified analog image signal is supplied to the source line after the source line is precharged, the second amount of current being less than the first amount of current,
• the gain unit comprises
• a first floating current source which drives the gain unit and has a third amount of current during the charge recycling period;
• a second floating current source which drives the gain unit and has a fourth amount of current during the driving period, the fourth amount of current being less than the third amount of current;
• a first floating voltage source that controls first quiescent current to be generated in the output unit and has a first voltage during the charge recycling period;
• and
• a second floating voltage source which controls second quiescent current to be generated in the output unit and has a second voltage during the driving period, the second voltage being less than the first voltage, and the amount of the first quiescent current is less than the amount of the second quiescent current.

A method of operating an output buffer included in a source driver of an LCD (liquid crystal display) device, the method comprising:

• generating control currents by amplifying the difference between voltages of an analog image signal and a signal output from the output buffer;
• outputting a signal obtained by amplifying the analog image signal in response to the control currents;
• increasing an amount of bias current for driving a differential amplification unit included in the output buffer and reducing an amount of quiescent current flowing through an output unit included in the output buffer during a charge recycling period in which a source line of the LCD device is precharged to a precharge voltage;
• and
• reducing the amount of the bias current for driving the differential amplification unit and increasing the amount of the quiescent current flowing through the output unit during a driving period in which the amplified analog image signal is supplied to the source line after the source line is precharged.

A source driver of an LCD (liquid crystal display) device, the source driver comprising:

• a gamma decoder transforming a digital image signal into an analog image signal and outputting the analog image signal;
• and
• an output unit amplifying and outputting the analog image signal,
• wherein an amount of bias current for driving a differential amplification unit of an output buffer increases and the amount of quiescent current flowing through an output unit of the output buffer decreases during a charge recycling period in which a source line of the LCD device is precharged to a precharge voltage, and
• the amount of the bias current for driving the differential amplification unit decreases and the amount of the quiescent current flowing through the output unit increases during a driving period in which the amplified analog image signal is supplied to the source line after the source line is precharged.