Liquid Crystal Display (LCD) devices and other display devices use a variety of techniques to generate voltages that correspond in some fashion to a gamma curve, which is a non-linear curve that maps pixel luminance values, such as pixel grey-level values, to drive voltage values.
A voltage generator circuit comprises a resistor string, a drive mechanism configured to drive a drive signal, a voltage feedback network, and a voltage tap point. The voltage tap point is located along the resistor string. The voltage tap point is configured to be selectively coupled simultaneously with the drive mechanism and the voltage feedback network, such that an output of the voltage tap point is selectively coupled with the drive mechanism via the voltage feedback network.
The drawings referred to in this Brief Description of Drawings should not be understood as being drawn to scale unless specifically noted. The accompanying drawings, which are incorporated in and form a part of the Description of Embodiments, illustrate various embodiments of the present invention and, together with the Description of Embodiments, serve to explain principles discussed below, where like designations denote like elements, and:
The following Description of Embodiments is merely provided by way of example and not of limitation. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
Herein, various embodiments and methods are described that facilitate improved usability of display devices and display device gamma voltage generator circuits. Discussion begins with description of some example gamma curves for a variety different display panels (e.g., Liquid Crystal Display panels). An example display device, which includes a display such as an LCD panel is then described. The display device includes a voltage generator circuit, some features of which are then described in greater detail. The voltage generator circuit is configured to generate gamma curve voltages which can be utilized for one or a variety of display panels. As will be describe the voltage generator circuit is configured to reduce voltage errors in gamma curve voltages by recusing errors in the drive signals that are driven on a resistor string of the voltage generator circuit. Operation of a voltage generator circuit is described in further detail in conjunction with description of controlling voltage generation.
In the embodiment illustrated in
In one embodiment, the gamma curve for which gamma curve voltages are generated may be selected from a set of gamma curves, for example gamma curve 110 may be selected from a plurality of gamma curves for a single display panel 210 (e.g., a red gamma curve for display panel 210, a blue gamma curve for display panel 210, a green gamma curve for display panel 210, etc.) and/or from a plurality of gamma curves for different displays (e.g., a red gamma curve for a display made by manufacturer A, a red gamma curve for a display made by manufacturer B, and a red gamma curve for a display made by manufacturer C, etc.). The selection may be based on the desired sub-pixel display color and/or the manufacturer. In other embodiments, a single gamma curve may be used. In further embodiments, the gamma curve may be hardwired within the circuitry and/or firmware of display device 200.
Gamma curve voltage selector 290 is configured to select a first gamma curve voltage from a set of gamma curve voltages 280 that comprise the plurality of gamma curve voltages, the second plurality of gamma curve voltages, and additional pluralities of gamma curve voltages when more than two resistive modules 275-1 to 275-n are utilized to form a resistor string 275. Gamma curve voltage selector 290 is further configured to couple the first gamma curve voltage with a respective pixel of pixel array 220 in display panel 210. The first and second pluralities of gamma curve voltages correspond to first and second subsets of a set of grey-level values. In one embodiment, the overall set of grey-level values may comprise 256 values. In other embodiments, different amounts of values may be used. In various embodiments, the grey-level values may be based on a grey-level code. For example, the 256 grey-level values may be based on an 8-bit grey-level code values. In other embodiments, other numbers of code values may be used.
In one embodiment, gamma curve voltage generator circuit 270, and corresponding resistive modules 275-1 to 275-n generate a different set of reference gamma curve voltages for each different gamma curve. In one embodiment, each sub-pixel color may have a corresponding gamma curve; for example, in one embodiment, a red gamma curve corresponding to red sub-pixels, a green gamma curve corresponding to green sub-pixels, and a blue gamma curve corresponding to blue sub-pixels. In another embodiment, a red gamma curve corresponding to red sub-pixels, a green gamma curve corresponding to green sub-pixels, a blue gamma curve corresponding to blue sub-pixels and a white gamma curve corresponding to white sub-pixels. In other embodiments, different display device manufacturers may have corresponding gamma curves. In yet further embodiments, each display device manufacture may have a gamma curve corresponding to each sub-pixel color. The gamma curves may be stored within a storage device, and may be selected based on the display device manufacturer and/or sub-pixel color to be displayed. In one embodiment, gamma curve voltage generator circuit 270 selects the gamma curve for which voltages are to be generated. In other embodiments, the gamma curve is selected externally from gamma curve voltage generator circuit 270 and communicated to gamma curve voltage generator circuit 270. External selection can take place at various times and locations. For example, in one embodiment, external selection of a gamma curve occurs as a part of manufacture of a display device 200. In another embodiment, gamma curve selection can occur just prior to generating gamma curve voltages during operation of display device 200.
In various embodiments, gamma curve voltage selector 290 is configured to select a gamma curve voltage 280 corresponding to the sub-pixel color to be displayed by display device 200. In one example embodiment, where there are 256 grey-level values, a gamma curve voltage selector 290 connects exactly one of these voltages to an associated pixel, according to the 8-bit value for that pixel's red, green or blue sub-pixel. Note that a given gamma curve voltage 280 output from gamma curve voltage generator circuit 270 may be connected to none of the pixels or to any number of the pixels. This depends on the sub-pixel data
Many factors may contribute to voltage errors when generating gamma curve voltages 280. Some of these factors include, but are not limited to: current draw of the load (display), current draw of the resistor string, resistances in the drive network over which a drive signal travels to drive a tap point (e.g., parasitic resistances of the wiring route that are in the route of the drive signal, resistances of switches that are the route of the drive signal, and other route resistances such as the resistance of vias that are in the route of the drive signal). The various resistances in the drive network may cause significant voltage errors in a tapped gamma curve voltage 280 due to significant IR drops. As many display devices can be very sensitive to variations in the supplied gamma curve voltage, circuit 270 utilizes a particularized form of feedback control to control the level of drive signal 315 at (or very close to) the tap point where drive signal 315 is driven onto resistor string 275. This feedback allows for controlling drive signal error at the tap point where the drive signal is applied to resistor string 275.
With reference to
Voltage tap points may be referred to generically herein as “tap points” or as “voltage tap points.” Even though either a voltage or current may be driven onto resistor string 275 via the voltage tap point, a gamma curve voltage 280 may be tapped at the voltage tap point regardless of whether a voltage or current drive signal 315 is driven. This is because resistor string 275 creates a plurality of tappable gamma curve voltages 280 whether driven by voltage or current.
In various embodiments, each voltage tap point 370 (370-0-370-n) is configured to be programmably selected to couple simultaneously with drive mechanism 320 and with voltage feedback network 340. In one embodiment, various voltage tap points may be fixed, such as voltage tap points at either end of resistor string 275. In various embodiments, a voltage tap point is programmably selected based on corresponding gamma curve voltages. For example, a voltage tap point of voltage tap points 370 may be programmably selected to output a gamma curve voltage or plurality of gamma curve voltages based on the gamma curve (i.e., gamma curve 110, 120, 130). In various embodiments, as the gamma curve changes, the voltage tap point programmably selected changes correspondingly.
A programmable reference 310, which is either a reference voltage or a reference current, is utilized to set the level of drive signal 315 (either a drive voltage or a drive current) which is driven by drive mechanism 320. The value of programmable reference 310 may be programmably altered during the operation of circuit 270 in order to alter the level of a voltage or current that is being driven as drive signal 315.
Drive mechanism 320 utilizes feedback control. This can be implemented in various manners. As illustrated, drive mechanism 320 is implemented as differential operational amplifier with feedback control. Drive mechanism 320 drives a signal based on a level of a programmable reference which is supplied as an input. Drive mechanism 320 may amplify the programmable reference 310 or may have its gain set such that it simply attempts to buffer the level of the programmable reference 310 as drive signal 315. The output of drive mechanism 320 may be a drive signal 315 that is either a voltage or a current, depending on the configuration of circuit 270. Drive signal 315 is coupled onto drive network 330 from the output of drive mechanism 320.
Tap select bus 350 and a decoder 360 (decoders 360-1, 360-2, 360-3, 360-n illustrated) operate to selectively open and close switches SW1A, SW2A, SW3A, to SWnA to couple drive network 330 either to no voltage tap point, or to only a single voltage tap point during any period of time. For example, if switch SW1A is closed, switches SW2A, SW3A, and SWnA are open. Switch SW1B corresponds to switch SW1A, and decoder 360-1 opens and closes switch SW1A and SW1B in concert with one another such that SW1A and SW1B are closed simultaneously and opened simultaneously. In a similar fashion decoder 360-2 operates switches SW2A and SW2B in concert; decoder 360-3 operates switches SW3A and SW3B in concert; and likewise decoder 360-n operates switches SWnA and SWnB in concert. Although separate decoders 360-1, 360-2, 360-3 . . . 360-n are illustrated with respect to the switches associated with each of voltage tap points 370-1, 370-2, 370-3 . . . 370-n, it is appreciated that other addressing schemes may be utilized. For example, signals may be multiplexed to switches SW1A-SWnA and to switches SW1B-SWnB. Additionally, other decoding mechanisms and/or configurations may be utilized. For example, a tree decoder may be utilized.
When switch SW1B is closed in concert with the closing of SW1A, voltage tap point 370-1 is coupled with feedback network 340 which couples a voltage that is output from voltage tap point 370-1 to the inverting input of drive mechanism 320. This voltage feeds back information about the actual level of drive signal 315 when it reaches voltage tap point 370-1. When switch SW2B is closed in concert with the closing of SW2A, voltage tap point 370-2 is coupled with feedback network 340 which couples a voltage that is output from voltage tap point 370-2 to the inverting input of drive mechanism 320. This voltage feeds back information about the actual level of drive signal 315 when it reaches voltage tap point 370-2. When switch SW3B is closed in concert with the closing of SW3A, voltage tap point 370-3 is coupled with feedback network 340 which couples a voltage that is output from voltage tap point 370-3 to the inverting input of drive mechanism 320. This voltage feeds back information about the actual level of drive signal 315 when it reaches voltage tap point 370-3. When switch SWnB is closed in concert with SWnA, voltage tap point 370-n is coupled with feedback network 340 which couples a voltage that is output from voltage tap point 370-n to the inverting input of drive mechanism 320. This voltage feeds back information about the actual level of drive signal 315 when it reaches voltage tap point 370-n. It is appreciated that circuit 270 may couple a first voltage tap point, such as voltage tap point 370-1, simultaneously with drive network 330 and feedback network 340 for a first period of time and then switch to coupling a second voltage tap point, such as voltage tap point 370-2, simultaneously with drive network 330 and feedback network 340 during a subsequent and non-overlapping period of time.
Consider the following non-limiting example of one possible operation of circuit 270. For purposes of this example only, programmable reference 310 is programmed to provide 2.3V at the non-inverting input of drive mechanism 320. Drive mechanism 320 is configured as a buffering amplifier with feedback, and initially outputs a drive signal 315 of 2.3V onto drive network 330. Decoder 360-1 decodes information from voltage tap select bus 350 that causes it to close switch SW1A, which allows drive mechanism 320 to drive a drive signal 315 through drive network 330 and onto voltage tap point 370-1. Simultaneously, to closing switch SW1A, decoder 360-1 also closes switch SW1B. This provides a feedback path from voltage tap point 370-1 to the inverting input of drive mechanism 320. This is a voltage feedback path as the input to the drive mechanism 320 has a practically infinite DC input impedance, and thus no current in the path regardless of the resistive elements in the path. Because there is no current flow, no additional errors are induced by feedback network 340. The feedback voltage provides a snapshot of the level of drive signal 315 that actually reaches voltage tap point 370-1. For example, drive signal 315 may have been reduced to a level of 2.25V due one or more resistances that exist in drive network 330 between the output of drive mechanism 320 and voltage tap point 370-1. Some non-limiting examples of these resistances which can induce error into drive signal 315 include: wiring resistance, resistance of one or more switches, and a routing resistance (e.g., resistance due to vias and other items in the route that drive signal 315 travels between drive mechanism 320 and voltage tap point 370-1). Based on this voltage feedback from voltage tap point 370-1, drive mechanism 320 adjust the level of its output so that a drive signal 315 of 2.3V actually arrives at voltage tap point 370-1. For example, based on continuous feedback via feedback network 340, drive mechanism 320 may eventually output a drive signal 315 such as 2.35V in order to overcome errors in drive network 330 to achieve a drive signal 315 of 2.3V at voltage tap point 370-1. This reduces, and in this example nullifies, the error(s) introduced into drive signal 315 by drive network 330.
At 410 of flow diagram 400, in one embodiment, a selected voltage tap point of a plurality of selectable voltage tap points is coupled simultaneously with a drive mechanism and a voltage feedback network, said plurality of selectable voltage tap points located along a resistor string. This coupling is performed by a switching mechanism. The switching mechanism may comprise switches which are selectively addressed/controlled, such as with decoder logic, multiplexed signals, or the like. With reference to
At 420 of flow diagram 400, in one embodiment, a drive signal is driven onto the resistor string via the selected voltage tap point. The drive signal is driven with the drive mechanism and can be either a voltage drive signal or a current drive signal. The drive mechanism can utilize a programmable reference voltage (or current) as in input for determining a voltage to drive onto the resistor string. The programmability allows different drive signal levels (e.g., different voltage levels or different current levels) to be programmably selected for driving onto a resistor string. For example, with reference to
At 430 of flow diagram 400, in one embodiment, an output is coupled from the selected voltage tap point as feedback to the drive mechanism via the feedback network. The output is a voltage and is the same as a gamma curve voltage 280 that may be tapped from this voltage tap point by a gamma curve voltage selector 290. For example, with reference to
At 440 of flow diagram 400, in one embodiment, feedback control is provided over the drive mechanism to control a level of the drive signal driven onto the resistor string at the selected voltage tap point. For example, as illustrated, drive mechanism 320 is set up as a differential amplifier and utilizes the voltage fed back from a voltage tap point, such as voltage tap point 370-1 as feedback to adjust the level of drive signal 315 until the signals at the inverting and non-inverting inputs equate to one another. It is appreciated that a feedback voltage can be converted to a current, if current feedback is required by drive mechanism 320. This feedback control reduces an error in the drive signal at the tap point. The errors that are reduced may be from one or some combination of sources and may include errors due to one or more of a wiring resistance, a switch resistance, and a routing resistance.
At 450 of flow diagram 400, in one embodiment, further comprises switching from coupling the selected voltage tap point simultaneously with the drive mechanism and the voltage feedback network to coupling a second selected voltage tap point of the plurality of selectable voltage tap points simultaneously with the drive mechanism and the voltage feedback network. The switching is performed by a switching mechanism, such as a plurality of addressable switches. For example, with reference to
The embodiments and examples set forth herein were presented in order to best explain the present invention and its particular application and to thereby enable those skilled in the art to make and use the invention. However, those skilled in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed.