The invention relates in general to a driving circuit, and more particularly to a display driving circuit.
Referring to
The positive gray scale display reference voltage generating circuits 12a, 12b and 12c respectively generate 256 positive gray scale display reference voltages for gamma correction of red color channels, 256 positive gray scale display reference voltages for gamma correction of green color channels and 256 positive gray scale display reference voltages for gamma correction of blue color channels according to the settings for the positive display reference voltages stored in the register 15. The negative gray scale display reference voltage generating circuits 12d, 12e and 12f respectively generate 256 negative gray scale display reference voltages for gamma correction of red color channels, 256 negative gray scale display reference voltages for gamma correction of green color channels and 256 negative gray scale display reference voltages for gamma correction of blue color channels according to the settings for the negative display reference voltages stored in the register 15.
The video signals of pixel data, R[7:0]/G[7:0]/B[7:0], are serially sent into the data latch. The data latch temporarily stores the pixel data of display line for each display channel. The outputs of the data latch are connected to the level shifter. The level shifter translates the power domain for the video signal. The DAC 13 outputs one of the display reference voltages to the buffer operational amplifier from the 256 display reference voltages generated by the gray scale reference voltage generating circuit according to it's input video signal. Finally, the multiplexer mux controlled by a polarity outputs a driving voltage Vo outputted from the buffer operational amplifier 18 to provide large driving ability to drive display device.
In order to independently adjust the gamma correction for each of the color channels (red, green, blue), the conventional display driving circuit 10 needs at least 3 sets of gray scale display reference voltage generating circuits, wherein each set of gray scale display reference voltage generating circuit comprises a positive gray scale display reference voltage generating circuit and a negative gray scale display reference voltage generating circuit. However, such design occupies large chip area and consumes a lot of power consumption. Furthermore, the conventional display driving circuit 10 needs considerable metal routing traces for the gray scale display reference voltages in the layout of the circuit.
The invention is related to a display driving circuit. The sets of display reference voltage generating circuits can be reduced while keeping the function of independently adjusting the gamma correction for each of the color channels. Therefore, the chip area and power consumption can be reduced. Furthermore, the number of metal routing traces in the layout can also be reduced to a great extent.
According to the present invention, a display driving circuit is provided. The display driving circuit comprises a video signal transformation circuit, a display reference voltage generating circuit, a digital to analog converter (DAC) and an interpolation operational amplifier. The video signal transformation circuit transforms an input video signal into a transformed video signal with a higher bit depth which already contains the information of gamma correction according to a lookup table (LUT). Then, the transformed video signals are serially sent into the data latch. The data latch temporarily stores the pixel data of display line for each display channel. The outputs of the data latch are connected to the level shifter. The level shifter translates the power domain for the transformed video signal. The transformed video signal from level shifter's output node is divided into upper n bits and lower m bits, wherein n+m is the bit depth of the transformed video signal. The upper n bits are connected to the input of the DAC and the lower m bits are connected to the input of the interpolation operational amplifier. The display reference voltage generating circuit generates a plurality of display reference voltages. The DAC outputs a first display reference voltage and a second display reference voltage to the interpolation operational amplifier from the display reference voltages generated by the display reference voltage generating circuits according to the upper n bits of the transformed video signal. Finally, the interpolation operational amplifier outputs a driving voltage to display device according to the first display reference voltage, the second display reference voltage and the lower m bits of the transformed video signal.
The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings.
A display driving circuit is disclosed in a number of embodiments below. The display driving circuit comprises a video signal transformation circuit, a display reference voltage generating circuit, a digital to analog converter (DAC) and an interpolation operational amplifier. The video signal transformation circuit transforms an input video signal into a transformed video signal higher bit depth which already contains the information of gamma correction according to a lookup table (LUT). Then, the transformed video signals are serially sent into the data latch. The data latch temporarily stores the pixel data of display line for each display channel. The outputs of the data latch are connected to the level shifter. The level shifter translates the power domain for the transformed video signal. The transformed video signal from level shifter's output node is divided into upper n bits and lower m bits, wherein n+m is the bit depth of the transformed video signal. The upper n bits are connected to the input of the DAC and the lower m bits are connected to the input of the interpolation operational amplifier. The display reference voltage generating circuit generates a plurality of display reference voltages. The DAC outputs a first display reference voltage and a second display reference voltage from the display reference voltages generated by the display reference voltage generating circuits according to the upper n bits of the transformed video signal. Finally, the interpolation operational amplifier outputs a driving voltage to display device according to the first display reference voltage, the second display reference voltage and the lower m bits of the transformed video signal.
Referring to
The lookup table records the one-to-one mapping relationships between the input video signals and the output transformed higher bit depth video signals. In the present embodiment of the invention, the bit depth of the input video signal is 8, and the bit depth of the output transformed video signal is 10. The mapping relationships recorded in the lookup table are the information for gamma correction of red/green/blue color channels.
The video signal transformation circuit 21 transforms an input video signal into a transformed video signal with a higher bit depth which already contains the information of gamma correction according to a lookup table (LUT) and a digital interpolation technique, wherein the bit depth of the transformed video signal is higher than that of input video signal. The transformed higher bit depth video signal is divided into upper n bits and lower m bits, wherein n+m is the bit depth of the transformed video signal. The upper n bits P1 comprise upper n bits from MSB direction of the transformed video signal, and the lower m bits P2 comprise the rest m bits of the transformed video signal, wherein n+m is the bit depth of the transformed video signal. The upper n bits P1 are sent to the DAC 23 as input signal through the data latch 26 and the level shifter 27, and the lower m bits P2 are sent to the interpolation operational amplifier 24 as input signal through the data latch 26 and the level shifter 27.
In the present embodiment of the invention, n and m are respectively exemplified by 6 and 4, and bit depth of the input video signal and that of the transformed video signal are respectively exemplified by 8 and 10. The input video signal is such as the video signal R[7:0] for red color channel, the video signal G[7:0] for green color channel or the video signal B[7:0] for blue color channel illustrated in
The positive display reference voltage generating circuit 22a generates a plurality of positive display reference voltages, and the negative display reference voltage generating circuit 22b generates a plurality of negative display reference voltages. For example, when the bit depth of the input video signal equals 8, the number of display reference voltages generated by the display reference voltage generating circuit for each color channel can be reduced to less than 28. In the present embodiment of the invention, the number of positive display reference voltages and that of negative display reference voltages respectively are exemplified by 26+1. The one extra reference voltage is used as one of the reference point for interpolation.
In comparison to the conventional display driving circuit 10, the display driving circuit 20 uses only one set of positive display reference voltage generating circuit and one set of negative display reference voltage generating circuit instead of three sets of positive display reference voltage generating circuits and three sets of negative display reference voltage generating circuits. In addition to reducing several sets of display reference voltage generating circuits, the display driving circuit 20 further reduces the chip area and power consumption. Furthermore, the number of metal routing traces in the layout of the circuit can also be reduced.
In the present embodiment of the invention, the number of bits of the DAC 23 is exemplified by 6. The upper 6 bits of the transformed video signal P1 from the level shifter are sent to the DAC 23 as input signal. Then, the DAC 23 outputs two adjacent display reference voltages, VH and VL, from 26+1 display reference voltages to the interpolation amplifier. The interpolation operational amplifier 24 outputs a driving voltage to display device according to the first display reference voltage VH, the second display reference voltage VL and the lower 4 bits of the transformed video signal P2.
Referring to
Referring to
output data value after interpolation process is given according to the data values xn, xm, and the corresponding transformed output data values yn, ym. The bit depth of the output signal of the video signal transformation circuit is greater than that of the input signal. In the present embodiment of the invention, the input and output video signals of the video signal transformation circuit are 8-bit and 10-bit respectively, and the lookup table records one-to-one mapping relationships between some of data values of the 8-bit input signal and the corresponding 10-bit output values. Only 26 out of 256 pairs of input/output one-to-one mapping relationships are recorded in the lookup table for a positive or a negative gamma correction curve. There are total 26*6 pairs of input/output one-to-one mapping relationships are recorded in the lookup table for gamma correction of all color channels. The data value of the 8-bit input signal, whose one-to-one mapping relationships can be found in the lookup table, is directly transformed into the 10-bit output data value by the lookup table unit while the data value of the 8-bit input signal, whose one-to-one mapping relationships cannot be found in the lookup table, is processed by the interpolation circuit to obtain the corresponding 10-bit output data value.
Referring to
The multiplexer 226 connected between the resistor string 221, and the input node of the buffer amplifier 228 selects a reference voltage from VR1_32˜VR1_63 as an input voltage of the buffer amplifier 228 according to control signal VGP2IN[4:0]. VGP2 is the output voltage of the buffer amplifier 228. The de-multiplexer 227 connected between the buffer amplifier 228 and the output voltage nodes VR2_32˜VR2_63_outputs VGP2 to one of the output voltage nodes VR2_32˜VR2_63 according to the control signal VGP2OUT[4:0]. The buffer amplifier 227 is connected between the multiplexer 226 and the de-multiplexer 227.
The voltages corresponding to the output voltage nodes VR2 _O˜VR2_64 form a reference voltage curve 6, which is piecewise linear, and the control signal VGP1IN[4:0], the control signal VGP1OUT[4:0], the control signal VGP2IN[4:0] and the control signal VGP2OUT[4:0] are for changing the slope of at least a part of the reference voltage curve 6. In the example of
The control signal VGP1IN[4:0] controls the multiplexer 223 to select the voltage VGP1 from VR1—1˜VR1_32, and the control signal VGP2IN[4:0] controls the multiplexer 226 to select the voltage VGP2 from VR1_32˜VR1_63. Thus, the slope of a part of the reference voltage curve 6 can be flexibly adjusted according to the control signal VGP1IN[4:0], the control signal VGP1OUT[4:0], the control signal VGP2IN[4:0] and the control signal VGP2OUT[4:0] so as to increase the output voltage resolution per step of the interpolation operational amplifier 24 within a particular voltage interval. Detailed circuits of the interpolation operational amplifier 24 can be implemented with reference to the U.S. Pat. No. US7,541,844B2, and the similarities are not repeated here.
Referring to
When P2 equals 0010, the driving voltage
When P2 equals 0011, the driving voltage
When P2 equals 0100, the driving voltage
When P2 equals 0101, the driving voltage
When P2 equals 0110, the driving voltage
When P2 equals 0111, the driving voltage
When P2 equals 1000, the driving voltage
When P2 equals 1001, the driving voltage
When P2 equals 1010, the driving voltage
When P2 equals 1011, the driving voltage
When P2 equals 1100, the driving voltage
When P2 equals 1101, the driving voltage
When P2 equals 1110, the driving voltage
When P2 equals 1111, the driving voltage
Therefore, the interpolation operational amplifier 24 can promptly output the driving voltage Vo corresponding to the higher bit depth transformed video signal according to the correspondence relationships illustrated in
While the invention has been described by way of example and in terms of the preferred embodiment(s), it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
Number | Date | Country | Kind |
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100103133 | Jan 2011 | TW | national |
This is a divisional application of co-pending U.S. Application No. 14/822,422, filed Aug. 10, 2015, which is a continuation application of U.S. U.S. Application Ser. No. 14/253,900 filed Apr. 16, 2014 (Now U.S. Pat. No. RE45,707 E). U.S. Application Ser. No. 14/253,900 claims the benefit of Taiwan application Serial No. 100103133, filed Jan. 27, 2011. The subject matter of these are incorporated herein by reference.
Number | Date | Country | |
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Parent | 14822422 | Aug 2015 | US |
Child | 16010242 | US |
Number | Date | Country | |
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Parent | 14253900 | Apr 2014 | US |
Child | 14822422 | US |
Number | Date | Country | |
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Parent | 13357197 | Jan 2012 | US |
Child | 14253900 | US |