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Patent Issued for Output Buffer Circuit Capable of Enhancing Stability

August 27, 2014

By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Hsu, Xie-Ren (Hsinchu, TW); Chen, Ji-Ting (Hsinchu County, TW); Kuo, Yao-Hung (Hsinchu, TW), filed on August 23, 2012, was published online on August 12, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8803600 is assigned to NOVATEK Microelectronics Corp. (Hsinchu Science Park, Hsin-Chu, TW).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to an output buffer circuit capable of enhancing stability, and more particularly to an output buffer circuit that increases a phase margin of an operational amplifier by adjusting output path impedance of the operational amplifier.

"Output buffers are usually applied to various electronic devices for isolating signals from input terminals to output terminals to avoid the input terminals being affected by loading and for enhancing driving ability. In Liquid Crystal Display (LCD) devices, for example, source drivers charge each pixel in LCD panels to an individual voltage level to drive liquid crystal molecules of each pixel by using the output buffers. Hence, the driving ability of the output buffer is highly related to display performance and responding time of the LCD devices.

"Please refer to FIG. 1, which is a schematic diagram of a conventional source driver 10. The source driver 10 includes a shift register 11, a data latch (or known as a line buffer) 12, a digital-to-analog converter (DAC) 13, an output buffer 14, and an output switch 15. The shift register 11 is utilized for sequentially receiving image data DATA according to a clock signal CLK. When the image data corresponding to a horizontal scan line data is received, the data latch 12 grabs the data temporarily stored in the shift register 11 according to a data loading signal LOAD generated by a timing controller (not shown), such that the shift register 11 can proceed to receive the image data of a next horizontal scan line. The DAC 13 then converts the digital pixel data stored in the data latch 12 to analog voltages and outputs the analog voltages to the output buffer 14. The output buffer 14 is utilized for providing sufficient driving ability, and the output switch 15 is utilized for sequentially coupling the output buffer 14 to a corresponding data line DL. Accordingly, the data line DL can be drove.

"In FIG. 1, the output buffer 14 and the output switch 15 is known as an output buffer circuit of the source driver 10. More specifically, as shown in FIG. 2, the output buffer 14 includes an operational amplifier 110, and the output switch 15 includes a switch SW for forming a signal path to the data line DL via an output pad P of the source driver 10. The operational amplifier 110 has a positive input terminal IN+, a negative input terminal IN- and an output terminal OUT. The positive input terminal IN+ is utilized for receiving an analog voltage. The output terminal OUTPUT is coupled to the negative input terminal IN- to form a negative feedback loop. The operational amplifier 110 is utilized for driving the voltage of the output pad P to a certain voltage level according to the analog voltage received by the positive input terminal IN+. However, in order to drive different pixels of the data line DL at different time, the source driver 10 must renew the analog voltage frequently. The source driver 10 turns off the switch SW when renewing the analog voltage, and turns on the switch SW for outputting the analog voltage being renewed to the data line DL until the data line DL is ready to be charged.

"When the switch SW is turned on, the output terminal OUT of the operational amplifier 110 is electrically connected to the data line DL through the output pad P. In general, the stabilization time of the output voltage is determined by capacitive load CLOAD of the date line DL, turn-on impedance of the switch SW and output impedance of the operational amplifier 110. However, in order to decrease power loss, the conventional source driver continuously reduces the DC currents of the output buffer, causing that a phase margin of the operational amplifier is decreased and thus the stabilization time is increased. Under this condition, it is inevitable to postpone the testing time of the output voltage, resulting in the increase of the testing cost."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "It is therefore an objective of the claimed invention to provide an output buffer circuit capable of enhancing stability.

"The present invention discloses an output buffer circuit capable of enhancing stability. The output buffer circuit includes an operational amplifier, a capacitive load, and an output control unit. The operational amplifier has a positive input terminal, a negative input terminal and an output terminal reversely coupled to the negative input terminal, and is utilized for generating an output voltage with a corresponding level to the output terminal according to an input voltage received by the positive input terminal. The output control unit is coupled between the output terminal of the operational amplifier and the capacitive load, and is utilized for controlling electrical connection between the output terminal of the operational amplifier and the capacitive load to form a signal output path and for adjusting the impedance of the signal output path when the signal output path is formed. The output control unit comprises a plurality of output switches, for individually turning on or off the electrical connection between the output terminal and the capacitive load of the operational amplifier, to form the signal output path, wherein the impedance of the signal output path is determined by quantity of turned-on output switches among the plurality of output switches.

"These and other objectives of the present invention will no doubt become obvious 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."

URL and more information on this patent, see: Hsu, Xie-Ren; Chen, Ji-Ting; Kuo, Yao-Hung. Output Buffer Circuit Capable of Enhancing Stability. U.S. Patent Number 8803600, filed August 23, 2012, and published online on August 12, 2014. Patent URL:

Keywords for this news article include: NOVATEK Microelectronics Corp.

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Source: Electronics Newsweekly

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