Abstract:
An analog buffer having voltage compensation mechanism is disclosed for use in a source driving circuit of a liquid crystal display. The analog buffer includes a reference voltage generator, a plurality of capacitors, a plurality of switches, and a plurality of transistors. Each of the capacitors is utilized to store the gate-source voltage of the corresponding turn-on transistor for performing gate-source voltage compensation operation based on the reference voltages provided by the reference voltage generator. Each of the switches functions to control gate-source voltage compensation operation and is turned on/off in response to a corresponding control signal. The analog buffer is capable of compensating the gate-source voltages of turn-on transistors for generating an output voltage having an acceptable tiny offset with respect to an input voltage.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an analog buffer, and more particularly, to an analog buffer with voltage compensation mechanism. 
         [0003]    2. Description of the Related Art 
         [0004]    Because liquid crystal display (LCD) devices are characterized by thin appearance, low power consumption, and low radiation, LCD devices have been widely applied in various electronic products for panel displaying. The operation of an LCD device is featured by varying voltage drops between opposite sides of the liquid crystal cells of the LCD device for twisting the angles of the liquid crystal molecules in the liquid crystal cells so that the transparency of the liquid crystal cells can be controlled for illustrating images with the aid of the light source provided by a backlight module. 
         [0005]    In general, the LCD device comprises a plurality of pixel units, a plurality of data lines and a source driver. The source driver comprises a plurality of source driving circuits. The source driving circuits perform latching operations, level shifting operations, digital-to-analog converting operations and analog signal buffering operations on the digital image data signals inputted to the LCD device for generating a plurality of analog signals. Each source driving circuit is coupled to a corresponding data line for writing the generated analog signals into corresponding pixel units. 
         [0006]    Accordingly, the analog buffer of each source driving circuit for performing the analog signal buffering operation functions as a key element for writing the generated analog signals into corresponding pixel units. With the aid of the analog buffers having enhanced driving ability for performing high-speed and accurate buffering operations, the LCD device is capable of providing high display quality. That is, the display quality of the LCD device is corresponding directly to the performance of the analog buffers. Furthermore, the source driver is installed with lots of analog buffers in that each source driving circuit should be installed with an individual analog buffer, and therefore a significant part of the layout area of the LCD device is required for accommodating the analog buffers. For that reason, simplified designs of the analog buffer and related control circuit without degrading the driving performance are required for realizing advanced low-cost LCD devices having thinner appearance. 
         [0007]      FIG. 1  is a schematic diagram showing the circuit of a conventional analog buffer for use in an LCD device. As shown in  FIG. 1 , the analog buffer  100  comprises an N-type metal-oxide-semiconductor (MOS) transistor  111 , a P-type MOS transistor  112 , a plurality of capacitors  121 - 124 , a plurality of switches  131 - 142 , and two current sources  181  and  182 . The analog buffer  100  is utilized to perform the analog signal buffering operation on an input voltage Vin for generating an output voltage Vout for charging the pixel capacitor Cpixel. However, the aforementioned conventional analog buffer is operated based on a variety of complicated control signals for controlling on/off states of the switches. Also, extra current control signals are required for controlling the current sources of the conventional analog buffer. That is, the circuit operation of the conventional analog buffer should be performed with the aid of complicated control circuits for generating the complicated control signals. In summary, the conventional analog buffer cannot meet the demand for designing advanced low-cost LCD devices having thinner appearance. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with an embodiment of the present invention, an analog buffer with voltage compensation mechanism is disclosed. The analog buffer comprises a first transistor, a second transistor, a first capacitor, a second capacitor, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch. 
         [0009]    The first transistor comprises a drain for receiving a first supply voltage, a source for outputting an output voltage, and a gate. The second transistor comprises a drain for receiving a second supply voltage, a source coupled to the source of the first transistor, and a gate. The first capacitor comprises a first end coupled to the gate of the first transistor, and a second end. The second capacitor comprises a first end coupled to the gate of the second transistor, and a second end. The first switch comprises a first end coupled to the second end of the first capacitor, and a second end coupled to the source of the first transistor. The second switch comprises a first end coupled to the second end of the second capacitor, and a second end coupled to the source of the second transistor. The third switch comprises a first end for receiving a first reference voltage, and a second end coupled to the first end of the first capacitor. The fourth switch comprises a first end for receiving a second reference voltage, and a second end coupled to the first end of the second capacitor. The fifth switch comprises a first end for receiving an input voltage, and a second end coupled to the second end of the first capacitor. The sixth switch comprises a first end for receiving the input voltage, and a second end coupled to the second end of the second capacitor. The analog buffer performs a voltage compensation operation for generating the output voltage based on the first reference voltage and the second reference voltage. 
         [0010]    In accordance with another embodiment of the present invention, an analog buffer with voltage compensation mechanism is disclosed. The analog buffer comprises a first transistor, a second transistor, a first capacitor, a second capacitor, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, a third capacitor, a fourth capacitor, a seventh switch, an eighth switch, a ninth switch, and a tenth switch. 
         [0011]    The first transistor comprises a drain for receiving a first supply voltage, a source for outputting an output voltage, and a gate. The second transistor comprises a drain for receiving a second supply voltage, a source coupled to the source of the first transistor, and a gate. The first capacitor comprises a first end coupled to the gate of the first transistor, and a second end. The second capacitor comprises a first end coupled to the gate of the second transistor, and a second end. The first switch comprises a first end coupled to the second end of the first capacitor, and a second end coupled to the source of the first transistor. The second switch comprises a first end coupled to the second end of the second capacitor, and a second end coupled to the source of the second transistor. The third switch comprises a first end for receiving a first reference voltage, and a second end coupled to the first end of the first capacitor. The fourth switch comprises a first end for receiving a second reference voltage, and a second end coupled to the first end of the second capacitor. The fifth switch comprises a first end for receiving an input voltage, and a second end coupled to the second end of the first capacitor. The sixth switch comprises a first end for receiving the input voltage, and a second end coupled to the second end of the second capacitor. The third capacitor comprises a first end coupled to the gate of the first transistor, and a second end. The fourth capacitor comprises a first end coupled to the gate of the second transistor, and a second end. The seventh switch comprises a first end coupled to the first end of the fifth switch, and a second end coupled to the second end of the third capacitor. The eighth switch comprises a first end coupled to the first end of the sixth switch, and a second end coupled to the second end of the fourth capacitor. The ninth switch comprises a first end coupled to the second end of the third capacitor, and a second end coupled to the source of the first transistor. The tenth switch comprises a first end coupled to the second end of the fourth capacitor, and a second end coupled to the source of the second transistor. The analog buffer performs a voltage compensation operation for generating the output voltage based on the first reference voltage and the second reference voltage. 
         [0012]    In accordance with another embodiment of the present invention, an analog buffer with voltage compensation mechanism is disclosed. The analog buffer comprises a first transistor, a second transistor, a first capacitor, a second capacitor, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, a third transistor, a fourth transistor, a seventh switch, an eighth switch, a ninth switch, and a tenth switch. 
         [0013]    The first transistor comprises a drain for receiving a first supply voltage, a source for outputting an output voltage, and a gate. The second transistor comprises a drain for receiving a second supply voltage, a source coupled to the source of the first transistor, and a gate. The first capacitor comprises a first end coupled to the gate of the first transistor, and a second end. The second capacitor comprises a first end coupled to the gate of the second transistor, and a second end. The first switch comprises a first end coupled to the second end of the first capacitor, and a second end coupled to the source of the first transistor. The second switch comprises a first end coupled to the second end of the second capacitor, and a second end coupled to the source of the second transistor. The third switch comprises a first end for receiving a first reference voltage, and a second end coupled to the first end of the first capacitor. The fourth switch comprises a first end for receiving a second reference voltage, and a second end coupled to the first end of the second capacitor. The fifth switch comprises a first end for receiving an input voltage, and a second end coupled to the second end of the first capacitor. The sixth switch comprises a first end for receiving the input voltage, and a second end coupled to the second end of the second capacitor. The third transistor comprises a drain for receiving a third supply voltage, a source coupled to the source of the first transistor, and a gate. The fourth transistor comprises a drain for receiving a fourth supply voltage, a source coupled to the source of the second transistor, and a gate. The seventh switch comprises a first end coupled to the gate of the third transistor, and a second end coupled to the source of the third transistor. The eighth switch comprises a first end coupled to the gate of the fourth transistor, and a second end coupled to the source of the fourth transistor. The ninth switch comprises a first end coupled to the gate of the first transistor, and a second end coupled to the gate of the third transistor. The tenth switch comprises a first end coupled to the gate of the second transistor, and a second end coupled to the gate of the fourth transistor. The analog buffer performs a voltage compensation operation for generating the output voltage based on the first reference voltage and the second reference voltage. 
         [0014]    In accordance with another embodiment of the present invention, an analog buffer with voltage compensation mechanism is disclosed. The analog buffer comprises a first transistor, a second transistor, a first capacitor, a second capacitor, a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, a third capacitor, a fourth capacitor, a seventh switch, an eighth switch, a ninth switch, a tenth switch, a third transistor, a fourth transistor, an eleventh switch, a twelfth switch, a thirteenth switch, and a fourteenth switch. 
         [0015]    The first transistor comprises a drain for receiving a first supply voltage, a source for outputting an output voltage, and a gate. The second transistor comprises a drain for receiving a second supply voltage, a source coupled to the source of the first transistor, and a gate. The first capacitor comprises a first end coupled to the gate of the first transistor, and a second end. The second capacitor comprises a first end coupled to the gate of the second transistor, and a second end. The first switch comprises a first end coupled to the second end of the first capacitor, and a second end coupled to the source of the first transistor. The second switch comprises a first end coupled to the second end of the second capacitor, and a second end coupled to the source of the second transistor. The third switch comprises a first end for receiving a first reference voltage, and a second end coupled to the first end of the first capacitor. The fourth switch comprises a first end for receiving a second reference voltage, and a second end coupled to the first end of the second capacitor. The fifth switch comprises a first end for receiving an input voltage, and a second end coupled to the second end of the first capacitor. The sixth switch comprises a first end for receiving the input voltage, and a second end coupled to the second end of the second capacitor. The third capacitor comprises a first end coupled to the gate of the first transistor, and a second end. The fourth capacitor comprises a first end coupled to the gate of the second transistor, and a second end. The seventh switch comprises a first end coupled to the first end of the fifth switch, and a second end coupled to the second end of the third capacitor. The eighth switch comprises a first end coupled to the first end of the sixth switch, and a second end coupled to the second end of the fourth capacitor. The ninth switch comprises a first end coupled to the second end of the third capacitor, and a second end coupled to the source of the first transistor. The tenth switch comprises a first end coupled to the second end of the fourth capacitor, and a second end coupled to the source of the second transistor. The third transistor comprises a drain for receiving a third supply voltage, a source coupled to the source of the first transistor, and a gate. The fourth transistor comprises a drain for receiving a fourth supply voltage, a source coupled to the source of the second transistor, and a gate. The eleventh switch comprises a first end coupled to the gate of the third transistor, and a second end coupled to the source of the third transistor. The twelfth switch comprises a first end coupled to the gate of the fourth transistor, and a second end coupled to the source of the fourth transistor. The thirteenth switch comprises a first end coupled to the gate of the first transistor, and a second end coupled to the gate of the third transistor. The fourteenth switch comprises a first end coupled to the gate of the second transistor, and a second end coupled to the gate of the fourth transistor. The analog buffer performs a voltage compensation operation for generating the output voltage based on the first reference voltage and the second reference voltage. 
         [0000]    These and other objectives of the present invention will no doubt become apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic diagram showing the circuit of a conventional analog buffer for use in an LCD device. 
           [0017]      FIG. 2  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a first embodiment of the present invention. 
           [0018]      FIG. 3  is a schematic circuit diagram showing a first embodiment of the reference voltage generator. 
           [0019]      FIG. 4  is a schematic circuit diagram showing a second embodiment of the reference voltage generator. 
           [0020]      FIG. 5  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 2 , having time along the abscissa. 
           [0021]      FIG. 6  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a second embodiment of the present invention. 
           [0022]      FIG. 7  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 6 , having time along the abscissa. 
           [0023]      FIG. 8  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a third embodiment of the present invention. 
           [0024]      FIG. 9  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 8 , having time along the abscissa. 
           [0025]      FIG. 10  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a fourth embodiment of the present invention. 
           [0026]      FIG. 11  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 10 , having time along the abscissa. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, it is to be noted that the present invention is not limited thereto. 
         [0028]      FIG. 2  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a first embodiment of the present invention. As shown in  FIG. 2 , the analog buffer  200  comprises a first transistor  211 , a second transistor  212 , a first capacitor  221 , a second capacitor  222 , a first switch  231 , a second switch  232 , a third switch  233 , a fourth switch  234 , a fifth switch  235 , a sixth switch  236 , a seventh switch  237 , an eighth switch  238 , a ninth switch  239 , a tenth switch  240 , and a reference voltage generator  290 . The reference voltage generator  290  is powered between a third supply voltage Vdd 2  and a fourth supply voltage Vss 2  for generating a first reference voltage Vb 1  and a second reference voltage Vb 2 . 
         [0029]    The first transistor  211  comprises a drain for receiving a first supply voltage Vdd 1 , a source for outputting an output voltage Vout, and a gate. The second transistor  212  comprises a drain for receiving a second supply voltage Vss 1 , a source coupled to the source of the first transistor  211 , and a gate. The first transistor  211  can be an N-type MOS transistor. The second transistor  212  can be a P-type MOS transistor, and the MOS transistor may be replaced by other components have similar functions. In the circuit operation of the analog buffer  200 , the first transistor  211  and the second transistor  212  are operated in the class-AB source-follower operation mode based on the common-drain configuration for lowering power consumption. 
         [0030]    The seventh switch  237  comprises a first end and a second end respectively coupled to the gate and source of the first transistor  211 . The eighth switch  238  comprises a first end and a second end respectively coupled to the gate and source of the second transistor  212 . The ninth switch  239  comprises a first end and a second end. The second end of the ninth switch  239  is coupled to the gate of the first transistor  211 . The tenth switch  240  comprises a first end and a second end. The second end of the tenth switch  240  is coupled to the gate of the second transistor  212 . The third switch  233  comprises a first end coupled to the reference voltage generator  290  for receiving the first reference voltage Vb 1 , and a second end coupled to the first end of the ninth switch  239 . The fourth switch  234  comprises a first end coupled to the reference voltage generator  290  for receiving the second reference voltage Vb 2 , and a second end coupled to the first end of the tenth switch  240 . 
         [0031]    The first capacitor  221  comprises a first end and a second end. The first end of the first capacitor  221  is coupled to the second end of the third switch  233 . The second capacitor  222  comprises a first end and a second end. The first end of the second capacitor  222  is coupled to the second end of the fourth switch  234 . The fifth switch  235  comprises a first end for receiving an input voltage Vin, and a second end coupled to the second end of the first capacitor  221 . The sixth switch  236  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the second capacitor  222 . The first switch  231  comprises a first end and a second end respectively coupled to the second end of the first capacitor  221  and the source of the first transistor  211 . The second switch  232  comprises a first end and a second end respectively coupled to the second end of the second capacitor  222  and the source of the second transistor  212 . 
         [0032]    In one embodiment, the internal circuit structure of the reference voltage generator  290  in  FIG. 2  can be designed as the reference voltage generator  300  shown in  FIG. 3 , which is a schematic circuit diagram showing a first embodiment of the reference voltage generator. As shown in  FIG. 3 , the reference voltage generator  300  comprises a first current source  311 , a second current source  312 , a first compensation diode  331  and a second compensation diode  332 . The first current source  311  comprises a first end for receiving the third supply voltage Vdd 2 , and a second end for providing a current  11 . The second current source  312  comprises a first end for receiving the fourth supply voltage Vss 2 , and a second end for providing a current  12 . The first compensation diode  331  comprises a positive end and a negative end. The positive end of the first compensation diode  331  is coupled to the second end of the first current source  311 . The second compensation diode  332  comprises a positive end coupled to the negative end of the first compensation diode  331 , and a negative end coupled to the second end of the second current source  312 . The first reference voltage Vb 1  and the second reference voltage Vb 2  are outputted respectively from the positive end of the first compensation diode  331  and the negative end of the second compensation diode  332 . 
         [0033]    In another embodiment, the internal circuit structure of the reference voltage generator  290  in  FIG. 2  can be designed as the reference voltage generator  400  shown in  FIG. 4 . Please refer to  FIG. 4 , which is a schematic circuit diagram showing a second embodiment of the reference voltage generator. As shown in  FIG. 4 , the reference voltage generator  400  comprises a first current source  411 , a second current source  412 , a first transistor  431  and a second transistor  432 . The first current source  411  comprises a first end for receiving the third supply voltage Vdd 2 , and a second end for providing a current  11 . The second current source  412  comprises a first end for receiving the fourth supply voltage Vss 2 , and a second end for providing a current  12 . The first transistor  431  comprises a drain coupled to the second end of the first current source  411 , a gate coupled to the drain, and a source. The second transistor  432  comprises a drain coupled to the second end of the second current source  412 , a gate coupled to the drain, and a source coupled to the source of the first transistor  431 . The first reference voltage Vb 1  and the second reference voltage Vb 2  are outputted respectively from the drain of the first transistor  431  and the drain of the second transistor  432 . The first transistor  431  can be an N-type MOS transistor. The second transistor  432  can be a P-type MOS transistor, and the MOS transistor may be replaced by other components having similar functions. 
         [0034]      FIG. 5  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 2 , having time along the abscissa. The signal waveforms in  FIG. 5 , from top to bottom, are the input voltage Vin, the first control signal P 1 , the second control signal P 2 , the first enable control signal Ea, the second enable control signal Eab, and the output voltage Vout. The first switch  231  through the fourth switch  234  are turned on/off in response to the first control signal P 1 . The fifth switch  235  and the sixth switch  236  are turned on/off in response to the second control signal P 2 . The ninth switch  239  and the tenth switch  240  are turned on/off in response to the first enable control signal Ea. The seventh switch  237  and the eighth switch  238  are turned on/off in response to the second enable control signal Eab. In the following description of the circuit operation concerning the related signal waveforms in  FIG. 5 , the enabled signal having high voltage level is utilized for turning on corresponding switches, and the disabled signal having low voltage level is utilized for turning off corresponding switches. The circuit operation of the analog buffer  200  is detailed as the followings. 
         [0035]    When the first control signal P 1  and the first enable control signal Ea are set to be enabled signals and the second control signal P 2  and the second enable control signal Eab are set to be disabled signals during the interval T 10 , the output voltage Vout is changed from the previous voltage V 0 ±ΔV 0  to the preset voltage Vpreset; meanwhile, the first capacitor  221  is charged to have the capacitor voltage as the gate-source voltage of the first transistor  211  in turn-on state, and the second capacitor  222  is charged to have the capacitor voltage as the gate-source voltage of the second transistor  212  in turn-on state. 
         [0036]    When the second control signal P 2  and the first enable control signal Ea are set to be enabled signals and the first control signal P 1  and the second enable control signal Eab are set to be disabled signals during the interval T 11 , the output voltage Vout is changed from the preset voltage Vpreset to the voltage V 1 ±ΔV 1  based on the voltage V 1  of the input voltage Vin in conjunction with the capacitor voltages of the first capacitor  221  and the second capacitor  222 . Since the gate-source voltages of the first transistor  211  and the second transistor  212  in turn-on state are compensated by the capacitor voltages of the first capacitor  221  and the second capacitor  222 , the variation error ΔV 1  can be lowered to an acceptable tiny offset with respect to the input voltage Vin. 
         [0037]    When the second enable control signal Eab is set to be an enabled signal and the first control signal P 1 , the second control signal P 2  and the first enable control signal Ea are set to be disabled signals during the interval T 12 , the first transistor  211  and the second transistor  212  are turned off for retaining the voltage V 1 ±ΔV 1  of the output voltage Vout and for saving power consumption corresponding to the first transistor  211  and the second transistor  212 . 
         [0038]    When the first control signal P 1  and the first enable control signal Ea are set to be enabled signals and the second control signal P 2  and the second enable control signal Eab are set to be disabled signals during the interval T 20 , the output voltage Vout is changed from the voltage V 1 ±ΔV 1  to the preset voltage Vpreset; meanwhile, the first capacitor  221  and the second capacitor  222  are charged to have the capacitor voltages respectively equal to the gate-source voltages of the first transistor  211  and the second transistor  212  in turn-on state. 
         [0039]    When the second control signal P 2  and the first enable control signal Ea are set to be enabled signals and the first control signal P 1  and the second enable control signal Eab are set to be disabled signals during the interval T 21 , the output voltage Vout is changed from the preset voltage Vpreset to the voltage V 2 ±ΔV 2  based on the voltage V 2  of the input voltage Vin in conjunction with the capacitor voltages of the first capacitor  221  and the second capacitor  222 . Since the gate-source voltages of the first transistor  211  and the second capacitor  222  in turn-on state are compensated by the capacitor voltages of the first capacitor  221  and the second capacitor  222 , the variation error ΔV 2  can be lowered to an acceptable tiny offset with respect to the input voltage Vin. 
         [0040]    When the second enable control signal Eab is set to be an enabled signal and the first control signal P 1 , the second control signal P 2  and the first enable control signal Ea are set to be disabled signals during the interval T 22 , the first transistor  211  and the second transistor  212  are turned off for retaining the voltage V 2 ±ΔV 2  of the output voltage Vout and for saving power consumption corresponding to the first transistor  211  and the second transistor  212 . 
         [0041]    Based on the above description, it is obvious that the seventh switch  237  through the tenth switch  240  are utilized to control on/off states of the first transistor  211  and the second transistor  212  for saving power consumption. If the design key issue of the analog buffer  200  is focused on production cost instead of power consumption, then the seventh switch  237  through the tenth switch  240  can be omitted for lowering production cost. That is, in another embodiment of the analog buffer  200 , the seventh switch  237  and the eighth switch  238  are replaced with open circuits, and the ninth switch  239  and the tenth switch  240  are replaced with short circuits, which is also applied to the following embodiments. It is noted that the enable signal and the disable signal are not limited to the signals having high voltage level and low voltage level respectively. In another embodiment, the enable signal and the disable signal can be set as the signals having low voltage level and high voltage level respectively without degrading the performance of the analog buffer. 
         [0042]      FIG. 6  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a second embodiment of the present invention. As shown in  FIG. 6 , the analog buffer  500  comprises a first transistor  511 , a second transistor  512 , a first capacitor  521 , a second capacitor  522 , a third capacitor  523 , a fourth capacitor  524 , a first switch  531 , a second switch  532 , a third switch  533 , a fourth switch  534 , a fifth switch  535 , a sixth switch  536 , a seventh switch  537 , an eighth switch  538 , a ninth switch  539 , a tenth switch  540 , an eleventh switch  541 , a twelfth switch  542 , a thirteenth switch  543 , a fourteenth switch  544 , a fifteenth switch  545 , and a reference voltage generator  590 . The reference voltage generator  590  is powered between a third supply voltage Vdd 2  and a fourth supply voltage Vss 2  for generating a first reference voltage Vb 1  and a second reference voltage Vb 2 . 
         [0043]    The first transistor  511  comprises a drain for receiving a first supply voltage Vdd 1 , a source for outputting an output voltage Vout, and a gate. The second transistor  512  comprises a drain for receiving a second supply voltage Vss 1 , a source coupled to the source of the first transistor  511 , and a gate. The first transistor  511  can be an N-type MOS transistor. The second transistor  512  can be a P-type MOS transistor. In the circuit operation of the analog buffer  500 , the first transistor  511  and the second transistor  512  are operated in the class-AB source-follower operation mode based on the common-drain configuration for lowering power consumption. 
         [0044]    The eleventh switch  541  comprises a first end and a second end respectively coupled to the gate and source of the first transistor  511 . The twelfth switch  542  comprises a first end and a second end respectively coupled to the gate and source of the second transistor  512 . The thirteenth switch  543  comprises a first end and a second end. The second end of the thirteenth switch  543  is coupled to the gate of the first transistor  511 . The fourteenth switch  544  comprises a first end and a second end. The second end of the fourteenth switch  544  is coupled to the gate of the second transistor  512 . The third capacitor  523  comprises a first end and a second end. The first end of the third capacitor  523  is coupled to the first end of the thirteenth switch  543 . The fourth capacitor  524  comprises a first end and a second end. The first end of the fourth capacitor  524  is coupled to the first end of the fourteenth switch  544 . The ninth switch  539  comprises a first end coupled to the second end of the third capacitor  523 , and a second end coupled to the source of the first transistor  511 . The tenth switch  540  comprises a first end coupled to the second end of the fourth capacitor  524 , and a second end coupled to the source of the second transistor  512 . 
         [0045]    The seventh switch  537  comprises a first end for receiving an input voltage Vin, and a second end coupled to the second end of the third capacitor  523 . The eighth switch  538  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the fourth capacitor  524 . The third switch  533  comprises a first end coupled to the reference voltage generator  590  for receiving the first reference voltage Vb 1 , and a second end coupled to the first end of the thirteenth switch  543 . The fourth switch  534  comprises a first end coupled to the reference voltage generator  590  for receiving the second reference voltage Vb 2 , and a second end coupled to the first end of the fourteenth switch  544 . 
         [0046]    The first capacitor  521  comprises a first end and a second end. The first end of the first capacitor  521  is coupled to the second end of the third switch  533 . The second capacitor  522  comprises a first end and a second end. The first end of the second capacitor  522  is coupled to the second end of the fourth switch  534 . The fifth switch  535  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the first capacitor  521 . The sixth switch  536  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the second capacitor  522 . The first switch  531  comprises a first end and a second end respectively coupled to the second end of the first capacitor  521  and the source of the first transistor  511 . The second switch  532  comprises a first end and a second end respectively coupled to the second end of the second capacitor  522  and the source of the second transistor  512 . The fifteenth switch  545  comprises a first end and a second end respectively coupled to the second end of the first capacitor  521  and the second end of the second capacitor  522 . 
         [0047]    In one embodiment, the internal circuit structure of the reference voltage generator  590  in  FIG. 6  can be designed as the reference voltage generator  300  shown in  FIG. 3 . In another embodiment, the internal circuit structure of the reference voltage generator  590  in  FIG. 6  can be designed as the reference voltage generator  400  shown in  FIG. 4 . 
         [0048]      FIG. 7  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 6 , having time along the abscissa. The signal waveforms in  FIG. 7 , from top to bottom, are the input voltage Vin, the first control signal P 1 , the second control signal P 2 , the third control signal P 3 , the first enable control signal Ea, the second enable control signal Eab, and the output voltage Vout. The first switch  531  through the fourth switch  534  are turned on/off in response to the first control signal P 1 . The fifth switch  535 , the sixth switch  536 , the ninth switch  539  and the tenth switch  540  are turned on/off in response to the second control signal P 2 . The seventh switch  537 , the eighth switch  538  and the fifteenth switch  545  are turned on/off in response to the third control signal P 3 . The thirteenth switch  543  and the fourteenth switch  544  are turned on/off in response to the first enable control signal Ea. The eleventh switch  541  and the twelfth switch  542  are turned on/off in response to the second enable control signal Eab. The circuit operation of the analog buffer  500  is detailed as the followings. 
         [0049]    When the first control signal P 1  and the first enable control signal Ea are set to be enabled signals and the second control signal P 2 , the third control signal P 3  and the second enable control signal Eab are set to be disabled signals during the interval T 10 , the output voltage Vout is changed from the previous voltage V 0 ±ΔV 02  to the preset voltage Vpreset; meanwhile, the first capacitor  521  is charged to have the capacitor voltage as the first gate-source voltage of the first transistor  511  in turn-on state, and the second capacitor  522  is charged to have the capacitor voltage as the second gate-source voltage of the second transistor  512  in turn-on state. 
         [0050]    When the second control signal P 2  and the first enable control signal Ea are set to be enabled signals and the first control signal P 1 , the third control signal P 3  and the second enable control signal Eab are set to be disabled signals during the interval T 11 , the output voltage Vout is changed from the preset voltage Vpreset to the voltage V 1 ±ΔV 11  based on the voltage V 1  of the input voltage Vin in conjunction with the capacitor voltages of the first capacitor  521  and the second capacitor  522 . Since the third gate-source voltage of the first transistor  511  in turn-on state is compensated by the capacitor voltage (the first gate-source voltage) of the first capacitor  521  and the fourth gate-source voltage of the second transistor  512  in turn-on state is compensated by the capacitor voltage (the second gate-source voltage) of the second capacitor  522 , the variation error is reduced to ΔV 11 . However, the third gate-source voltage and the fourth gate-source voltage are not completely compensated by the first gate-source voltage and the second gate-source voltage respectively. Consequently, the third capacitor  523  and the fourth capacitor  524  are charged to have the capacitor voltages respectively equal to the third gate-source voltage and the fourth gate-source voltage during the interval T 11  for the following compensation operation. 
         [0051]    When the third control signal P 3  and the first enable control signal Ea are set to be enabled signals and the first control signal P 1 , the second control signal P 2  and the second enable control signal Eab are set to be disabled signals during the interval T 12 , the fifteenth switch  545  is turned on for shorting the second ends of the first capacitor  521  and the second capacitor  522  so that the third capacitor  523  and the fourth capacitor  524  are capable of holding the third gate-source voltage and the fourth gate-source voltage respectively for performing accurate compensation operation. Then, the output voltage Vout is changed from the voltage V 1 ±ΔV 11  to the voltage V 1 ΔV 12  based on the voltage V 1  of the input voltage Vin in conjunction with the capacitor voltages (the third gate-source voltage and the fourth gate-source voltage) of the third capacitor  523  and the fourth capacitor  524 . That is, the accurate compensation operation reduces the variation error from ΔV 11  to ΔV 12  for generating the output voltage Vout having an acceptable tiny offset with respect to the input voltage Vin. 
         [0052]    When the second enable control signal Eab is set to be an enabled signal and the first control signal P 1 , the second control signal P 2 , the third control signal P 3  and the first enable control signal Ea are set to be disabled signals during the interval T 13 , the first transistor  511  and the second transistor  512  are turned off for retaining the voltage V 1 ±ΔV 12  of the output voltage Vout and for saving power consumption corresponding to the first transistor  511  and the second transistor  512 . The circuit operations of the analog buffer  500  from the interval T 20  to the interval T 23  are similar to the aforementioned circuit operations from the interval T 10  to the interval T 13 , and for the sake of brevity, further similar description is omitted. 
         [0053]      FIG. 8  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a third embodiment of the present invention. As shown in  FIG. 8 , the analog buffer  600  comprises a first transistor  611 , a second transistor  612 , a third transistor  613 , a fourth transistor  614 , a first capacitor  621 , a second capacitor  622 , a first switch  631 , a second switch  632 , a third switch  633 , a fourth switch  634 , a fifth switch  635 , a sixth switch  636 , a seventh switch  637 , an eighth switch  638 , a ninth switch  639 , a tenth switch  640 , an eleventh switch  641 , a twelfth switch  642 , a thirteenth switch  643 , a fourteenth switch  644  and a reference voltage generator  690 . The reference voltage generator  690  is powered between a third supply voltage Vdd 2  and a fourth supply voltage Vss 2  for generating a first reference voltage Vb 1  and a second reference voltage Vb 2 . 
         [0054]    The first transistor  611  comprises a drain for receiving a first supply voltage Vdd 1 , a source for outputting an output voltage Vout, and a gate. The second transistor  612  comprises a drain for receiving a second supply voltage Vss 1 , a source coupled to the source of the first transistor  611 , and a gate. The third transistor  613  comprises a drain for receiving a fifth supply voltage Vdd 3 , a source coupled to the source of the first transistor  611 , and a gate. The fourth transistor  614  comprises a drain for receiving a sixth supply voltage Vss 3 , a source coupled to the source of the second transistor  612 , and a gate. In the circuit operation of the analog buffer  600 , the fifth supply voltage Vdd 3  can be set to be greater than the first supply voltage Vdd 1 , and the sixth supply voltage Vss 3  can be set to be less than the second supply voltage Vss 1  for achieving high-speed voltage adjusting performance while performing auxiliary capacitor charge operations by making use of the third transistor  613  and the fourth transistor  614 . 
         [0055]    The first transistor  611  and the third transistor  613  can be N-type MOS transistors. The second transistor  612  and the fourth transistor  614  can be P-type MOS transistors. In the circuit operation of the analog buffer  600 , the first transistor  611 , the second transistor  612 , the third transistor  613  and the fourth transistor  614  are operated in the class-AB source-follower operation mode based on the common-drain configuration for lowering power consumption. 
         [0056]    The seventh switch  637  comprises a first end and a second end respectively coupled to the gate and source of the third transistor  613 . The eighth switch  638  comprises a first end and a second end respectively coupled to the gate and source of the fourth transistor  614 . The ninth switch  639  comprises a first end coupled to the gate of the first transistor  611 , and a second end coupled to the gate of the third transistor  613 . The tenth switch  640  comprises a first end coupled to the gate of the second transistor  612 , and a second end coupled to the gate of the fourth transistor  614 . The eleventh switch  641  comprises a first end and a second end respectively coupled to the gate and source of the first transistor  611 . The twelfth switch  642  comprises a first end and a second end respectively coupled to the gate and source of the second transistor  612 . 
         [0057]    The thirteenth switch  643  comprises a first end and a second end. The second end of the thirteenth switch  643  is coupled to the gate of the first transistor  611 . The fourteenth switch  644  comprises a first end and a second end. The second end of the fourteenth switch  644  is coupled to the gate of the second transistor  612 . The third switch  633  comprises a first end coupled to the reference voltage generator  690  for receiving the first reference voltage Vb 1 , and a second end coupled to the first end of the thirteenth switch  643 . The fourth switch  634  comprises a first end coupled to the reference voltage generator  690  for receiving the second reference voltage Vb 2 , and a second end coupled to the first end of the fourteenth switch  644 . 
         [0058]    The first capacitor  621  comprises a first end and a second end. The first end of the first capacitor  621  is coupled to the second end of the third switch  633 . The second capacitor  622  comprises a first end and a second end. The first end of the second capacitor  622  is coupled to the second end of the fourth switch  634 . The fifth switch  635  comprises a first end for receiving an input voltage Vin, and a second end coupled to the second end of the first capacitor  621 . The sixth switch  636  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the second capacitor  622 . The first switch  631  comprises a first end and a second end respectively coupled to the second end of the first capacitor  621  and the source of the first transistor  611 . The second switch  632  comprises a first end and a second end respectively coupled to the second end of the second capacitor  622  and the source of the second transistor  612 . 
         [0059]    In one embodiment, the internal circuit structure of the reference voltage generator  690  in  FIG. 8  can be designed as the reference voltage generator  300  shown in  FIG. 3 . In another embodiment, the internal circuit structure of the reference voltage generator  690  in  FIG. 8  can be designed as the reference voltage generator  400  shown in  FIG. 4 . 
         [0060]      FIG. 9  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 8 , having time along the abscissa. The signal waveforms in  FIG. 9 , from top to bottom, are the input voltage Vin, the first control signal P 1 , the second control signal P 2 , the first enable control signal Ea, the second enable control signal Eab, the third enable control signal Q 1 , the fourth enable control signal Q 1   b,  and the output voltage Vout. The first switch  631  through the fourth switch  634  are turned on/off in response to the first control signal P 1 . The fifth switch  635  and the sixth switch  636  are turned on/off in response to the second control signal P 2 . The thirteenth switch  643  and the fourteenth switch  644  are turned on/off in response to the first enable control signal Ea. The eleventh switch  641  and the twelfth switch  642  are turned on/off in response to the second enable control signal Eab. The ninth switch  639  and the tenth switch  640  are turned on/off in response to the third enable control signal Q 1 . The seventh switch  637  and the eighth switch  638  are turned on/off in response to the fourth enable control signal Q 1   b.  The circuit operation of the analog buffer  600  is detailed as the followings. 
         [0061]    When the first control signal P 1 , the first enable control signal Ea and the third enable control signal Q 1  are set to be enabled signals and the second control signal P 2 , the second enable control signal Eab and the fourth enable control signal Q 1   b  are set to be disabled signals during the interval T 10 , the output voltage Vout is changed from the previous voltage V 0 ±ΔV 0  to the preset voltage Vpreset; meanwhile, the first capacitor  621  is charged to have the capacitor voltage as the gate-source voltage of the first transistor  611  and the third transistor  613  in turn-on state, and the second capacitor  622  is charged to have the capacitor voltage as the gate-source voltage of the second transistor  612  and the fourth transistor  614  in turn-on state. Since the voltage adjustments of the capacitor voltages of the first capacitor  621  and the second capacitor  622  are performed via the first transistor  611  through the fourth transistor  614 , the charging operations for the first capacitor  621  and the second capacitor  622  can be carried out much faster for shortening the interval T 10  so that the analog buffer  600  is able to perform analog signal buffering operations at a higher speed. 
         [0062]    When the second control signal P 2 , the first enable control signal Ea and the fourth enable control signal Q 1   b  are set to be enabled signals and the first control signal P 1 , the second enable control signal Eab and the third enable control signal Q 1  are set to be disabled signals during the interval T 11 , the output voltage Vout is changed from the preset voltage Vpreset to the voltage V 1 ±ΔV 1  based on the voltage V 1  of the input voltage Vin in conjunction with the capacitor voltages of the first capacitor  621  and the second capacitor  622 . Since the gate-source voltages of the first transistor  611  through the fourth transistor  614  in turn-on state are compensated by the capacitor voltages of the first capacitor  621  and the second capacitor  622 , the variation error ΔV 1  can be lowered to an acceptable tiny offset with respect to the input voltage Vin. 
         [0063]    When the second enable control signal Eab and the fourth enable control signal Q 1   b  are set to be enabled signals and the first control signal P 1 , the second control signal P 2 , the first enable control signal Ea and the third enable control signal Q 1  are set to be disabled signals during the interval T 12 , the first transistor  611  through the fourth transistor  614  are turned off for retaining the voltage V 1 ±ΔV 1  of the output voltage Vout and for saving power consumption corresponding to the first transistor  611  through the fourth transistor  614 . The circuit operations of the analog buffer  600  from the interval T 20  to the interval T 22  are similar to the aforementioned circuit operations from the interval T 10  to the interval T 12 , and for the sake of brevity, further similar description is omitted. 
         [0064]    In an alternative circuit operation of the analog buffer  600 , the second control signal P 2 , the first enable control signal Ea and the third enable control signal Q 1  are set to be enabled signals and the first control signal P 1 , the second enable control signal Eab and the fourth enable control signal Q 1   b  are set to be disabled signals during the interval T 11  so that the analog buffer  600  is able to perform analog signal buffering operations at a much higher speed by turning on the first transistor  611  through the fourth transistor  614  for fast changing the output voltage Vout from the preset voltage Vpreset to the voltage V 1 ±ΔV 1  for shortening the interval T 11 . 
         [0065]      FIG. 10  is a schematic diagram showing the circuit of an analog buffer having voltage compensation mechanism in accordance with a fourth embodiment of the present invention. As shown in  FIG. 10 , the analog buffer  700  comprises a first transistor  711 , a second transistor  712 , a third transistor  713 , a fourth transistor  714 , a first capacitor  721 , a second capacitor  722 , a third capacitor  723 , a fourth capacitor  724 , a first switch  731 , a second switch  732 , a third switch  733 , a fourth switch  734 , a fifth switch  735 , a sixth switch  736 , a seventh switch  737 , an eighth switch  738 , a ninth switch  739 , a tenth switch  740 , an eleventh switch  741 , a twelfth switch  742 , a thirteenth switch  743 , a fourteenth switch  744 , a fifteenth switch  745 , a sixteenth switch  746 , a seventeenth switch  747 , an eighteenth switch  748 , a nineteenth switch  749  and a reference voltage generator  790 . The reference voltage generator  790  is powered between a third supply voltage Vdd 2  and a fourth supply voltage Vss 2  for generating a first reference voltage Vb 1  and a second reference voltage Vb 2 . 
         [0066]    The first transistor  711  comprises a drain for receiving a first supply voltage Vdd 1 , a source for outputting an output voltage Vout, and a gate. The second transistor  712  comprises a drain for receiving a second supply voltage Vss 1 , a source coupled to the source of the first transistor  711 , and a gate. The third transistor  713  comprises a drain for receiving a fifth supply voltage Vdd 3 , a source coupled to the source of the first transistor  711 , and a gate. The fourth transistor  714  comprises a drain for receiving a sixth supply voltage Vss 3 , a source coupled to the source of the second transistor  712 , and a gate. Similarly, in the circuit operation of the analog buffer  700 , the fifth supply voltage Vdd 3  can be set to be greater than the first supply voltage Vdd 1 , and the sixth supply voltage Vss 3  can be set to be less than the second supply voltage Vss 1  for achieving high-speed voltage adjusting performance while performing auxiliary capacitor charge operations by making use of the third transistor  713  and the fourth transistor  714 . 
         [0067]    The first transistor  711  and the third transistor  713  can be N-type MOS transistors. The second transistor  712  and the fourth transistor  714  can be P-type MOS transistors. In the circuit operation of the analog buffer  700 , the first transistor  711 , the second transistor  712 , the third transistor  713  and the fourth transistor  714  are operated in the class-AB source-follower operation mode based on the common-drain configuration for lowering power consumption. 
         [0068]    The eleventh switch  741  comprises a first end and a second end respectively coupled to the gate and source of the third transistor  713 . The twelfth switch  742  comprises a first end and a second end respectively coupled to the gate and source of the fourth transistor  714 . The thirteenth switch  743  comprises a first end coupled to the gate of the first transistor  711 , and a second end coupled to the gate of the third transistor  713 . The fourteenth switch  744  comprises a first end coupled to the gate of the second transistor  712 , and a second end coupled to the gate of the fourth transistor  714 . The fifteenth switch  745  comprises a first end and a second end respectively coupled to the gate and source of the first transistor  711 . The sixteenth switch  746  comprises a first end and a second end respectively coupled to the gate and source of the second transistor  712 . 
         [0069]    The seventeenth switch  747  comprises a first end and a second end. The second end of the seventeenth switch  747  is coupled to the gate of the first transistor  711 . The eighteenth switch  748  comprises a first end and a second end. The second end of the eighteenth switch  748  is coupled to the gate of the second transistor  712 . The third capacitor  723  comprises a first end and a second end. The first end of the third capacitor  723  is coupled to the first end of the seventeenth switch  747 . The fourth capacitor  724  comprises a first end and a second end. The first end of the fourth capacitor  724  is coupled to the first end of the eighteenth switch  748 . The ninth switch  739  comprises a first end coupled to the second end of the third capacitor  723 , and a second end coupled to the source of the first transistor  711 . The tenth switch  740  comprises a first end coupled to the second end of the fourth capacitor  724 , and a second end coupled to the source of the second transistor  712 . 
         [0070]    The seventh switch  737  comprises a first end for receiving an input voltage Vin, and a second end coupled to the second end of the third capacitor  723 . The eighth switch  738  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the fourth capacitor  724 . The first capacitor  721  comprises a first end and a second end. The first end of the first capacitor  721  is coupled to the first end of the seventeenth switch  747 . The second capacitor  722  comprises a first end and a second end. The first end of the second capacitor  722  is coupled to the first end of the eighteenth switch  748 . The third switch  733  comprises a first end coupled to the reference voltage generator  790  for receiving the first reference voltage Vb 1 , and a second end coupled to the first end of the first capacitor  721 . The fourth switch  734  comprises a first end coupled to the reference voltage generator  790  for receiving the second reference voltage Vb 2 , and a second end coupled to the first end of the second capacitor  722 . 
         [0071]    The fifth switch  735  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the first capacitor  721 . The sixth switch  736  comprises a first end for receiving the input voltage Vin, and a second end coupled to the second end of the second capacitor  722 . The first switch  731  comprises a first end and a second end respectively coupled to the second end of the first capacitor  721  and the source of the first transistor  711 . The second switch  732  comprises a first end and a second end respectively coupled to the second end of the second capacitor  722  and the source of the second transistor  712 . The nineteenth switch  749  comprises a first end and a second end respectively coupled to the second end of the first capacitor  721  and the second end of the second capacitor  722 . 
         [0072]    In one embodiment, the internal circuit structure of the reference voltage generator  790  in  FIG. 10  can be designed as the reference voltage generator  300  shown in  FIG. 3 . In another embodiment, the internal circuit structure of the reference voltage generator  790  in  FIG. 10  can be designed as the reference voltage generator  400  shown in  FIG. 4 . 
         [0073]      FIG. 11  shows the related signal waveforms concerning the circuit operation of the analog buffer in  FIG. 10 , having time along the abscissa. The signal waveforms in  FIG. 11 , from top to bottom, are the input voltage Vin, the first control signal P 1 , the second control signal P 2 , the third control signal P 3 , the first enable control signal Ea, the second enable control signal Eab, the third enable control signal Q 1 , the fourth enable control signal Q 1   b,  and the output voltage Vout. The first switch  731  through the fourth switch  734  are turned on/off in response to the first control signal P 1 . The fifth switch  735 , the sixth switch  736 , the ninth switch  739  and the tenth switch  740  are turned on/off in response to the second control signal P 2 . The seventh switch  737 , the eighth switch  738  and the nineteenth switch  749  are turned on/off in response to the third control signal P 3 . The seventeenth switch  747  and the eighteenth switch  748  are turned on/off in response to the first enable control signal Ea. The fifteenth switch  745  and the sixteenth switch  746  are turned on/off in response to the second enable control signal Eab. The thirteenth switch  743  and the fourteenth switch  744  are turned on/off in response to the third enable control signal Q 1 . The eleventh switch  741  and the twelfth switch  742  are turned on/off in response to the fourth enable control signal Q 1   b.  The circuit operation of the analog buffer  700  is detailed as the followings. 
         [0074]    When the first control signal P 1 , the first enable control signal Ea and the third enable control signal Q 1  are set to be enabled signals and the second control signal P 2 , the third control signal P 3 , the second enable control signal Eab and the fourth enable control signal Q 1   b  are set to be disabled signals during the interval T 10 , the output voltage Vout is changed from the previous voltage V 0 ±ΔV 02  to the preset voltage Vpreset; meanwhile, the first capacitor  721  is charged to have the capacitor voltage as the first gate-source voltage of the first transistor  711  and the third transistor  713  in turn-on state, and the second capacitor  722  is charged to have the capacitor voltage as the second gate-source voltage of the second transistor  712  and the fourth transistor  714  in turn-on state. Since the voltage adjustments of the capacitor voltages of the first capacitor  721  and the second capacitor  722  are performed via the first transistor  711  through the fourth transistor  714 , the charging operations for the first capacitor  721  and the second capacitor  722  can be carried out much faster for shortening the interval T 10  so that the analog buffer  700  is able to perform analog signal buffering operations at a higher speed. 
         [0075]    When the second control signal P 2 , the first enable control signal Ea and the fourth enable control signal Q 1   b  are set to be enabled signals and the first control signal P 1 , the third control signal P 3 , the second enable control signal Eab and the third enable control signal Q 1  are set to be disabled signals during the interval T 11 , the output voltage Vout is changed from the preset voltage Vpreset to the voltage V 1 ±ΔV 11  based on the voltage V 1  of the input voltage Vin in conjunction with the capacitor voltages of the first capacitor  721  and the second capacitor  722 . Since the third gate-source voltage of the first transistor  711  and the third transistor  713  in turn-on state is compensated by the capacitor voltage (the first gate-source voltage) of the first capacitor  721  and the fourth gate-source voltage of the second transistor  712  and the fourth transistor  714  in turn-on state is compensated by the capacitor voltage (the second gate-source voltage) of the second capacitor  722 , the variation error is reduced to ΔV 11 . However, the third gate-source voltage and the fourth gate-source voltage are not completely compensated by the first gate-source voltage and the second gate-source voltage respectively. Consequently, the third capacitor  723  and the fourth capacitor  724  are charged to have the capacitor voltages respectively equal to the third gate-source voltage and the fourth gate-source voltage during the interval T 11  for the following compensation operation. 
         [0076]    When the third control signal P 3 , the first enable control signal Ea and the fourth enable control signal Q 1   b  are set to be enabled signals and the first control signal P 1 , the second control signal P 2 , the second enable control signal Eab and the third enable control signal Q 1  are set to be disabled signals during the interval T 12 , the nineteenth switch  749  is turned on for shorting the second ends of the first capacitor  721  and the second capacitor  722  so that the third capacitor  723  and the fourth capacitor  724  are capable of holding the third gate-source voltage and the fourth gate-source voltage respectively for performing accurate compensation operation. Then, the output voltage Vout is changed from the voltage V 1 ±ΔV 11  to the voltage V 1 ±ΔV 12  based on the voltage V 1  of the input voltage Vin in conjunction with the capacitor voltages (the third gate-source voltage and the fourth gate-source voltage) of the third capacitor  723  and the fourth capacitor  724 . That is, the accurate compensation operation reduces the variation error from ΔV 11  to ΔV 12  for generating the output voltage Vout having an acceptable tiny offset with respect to the input voltage Vin. 
         [0077]    When the second enable control signal Eab and the fourth enable control signal Q 1   b  are set to be enabled signals and the first control signal P 1 , the second control signal P 2 , the third control signal P 3 , the first enable control signal Ea and the third enable control signal Q 1  are set to be disabled signals during the interval T 13 , the first transistor  711  through the fourth transistor  714  are turned off for retaining the voltage V 1 ±ΔV 12  of the output voltage Vout and for saving power consumption corresponding to the first transistor  711  through the fourth transistor  714 . The circuit operations of the analog buffer  700  from the interval T 20  to the interval T 23  are similar to the aforementioned circuit operations from the interval T 10  to the interval T 13 , and for the sake of brevity, further similar description is omitted. 
         [0078]    In an alternative circuit operation of the analog buffer  700 , the second control signal P 2 , the first enable control signal Ea and the third enable control signal Q 1  are set to be enabled signals and the first control signal P 1 , the third control signal P 3 , the second enable control signal Eab and the fourth enable control signal Q 1   b  are set to be disabled signals during the interval T 11  so that the analog buffer  700  is able to perform analog signal buffering operations at a much higher speed by turning on the first transistor  711  through the fourth transistor  714  for fast changing the output voltage Vout from the preset voltage Vpreset to the voltage V 1 ±ΔV 11  for shortening the interval T 11 . 
         [0079]    Furthermore, in an alternative circuit operation of the analog buffer  700 , the third control signal P 3 , the first enable control signal Ea and the third enable control signal Q 1  are set to be enabled signals and the first control signal P 1 , the second control signal P 2 , the second enable control signal Eab and the fourth enable control signal Q 1   b  are set to be disabled signals during the interval T 12  so that the analog buffer  700  is able to perform analog signal buffering operations at a much higher speed by turning on the first transistor  711  through the fourth transistor  714  for fast changing the output voltage Vout from the voltage V 1 ±ΔV 11  to the voltage V 1 ±ΔV 12  for shortening the interval T 12 . However, the voltage difference between the voltage V 1 ±ΔV 11  and the voltage V 1 ±ΔV 12  is substantially quite small, and therefore the reduced time of the shortened interval T 12  are quite limited, which is paid by much higher power consumption caused by the third transistor  713  and the fourth transistor  714  in turn-on state. Accordingly, in a preferred circuit operation of the analog buffer  700 , the third transistor  713  and the fourth transistor  714  are turned off for saving power consumption during the interval T 12 . 
         [0080]    The present invention is by no means limited to the embodiments as described above by referring to the accompanying drawings, which may be modified and altered in a variety of different ways without departing from the scope of the present invention. Thus, it should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations might occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.