Power management using automatic load/unload detection of DAC

An automatic load detection system. A first reference signal that may be known apriori can be used for load detection. For example, the first reference signal may be used for invisible portion of a frame. The DAC receives the first reference signal and outputs a signal that is based on the first reference signal. The output of the DAC may have two known values depending on whether the load is coupled to the DAC, e.g., by having a different impedance. Thus, the output signal may be used for detecting whether the load is uncoupled from the DAC. If it is determined that the load is uncoupled from the DAC, the clocking signal to the DAC may be turned off. Thus, DAC no longer consumes power when the load is uncoupled, thereby saving power.

TECHNICAL FIELD

The embodiments of the present invention relate to the field of power management in electronic devices.

BACKGROUND ART

Use of various electronic devices has increased substantially in recent years. For example, use of laptops, mobile telephones, Blackberrys, pagers, IPods, IPhone, etc. have become common in public places such as coffee shops, restaurants, college campuses, businesses, etc.

In general, most electronic devices are capable of rendering graphical content. Accordingly, most electronic devices are equipped with chips that display graphical content, e.g., graphical processing unit (GPU), application processor chips, etc. GPUs, application processor chips, etc. generally employ at least one digital to analog converter (DAC) to drive pixel data to a load, e.g., video receiver, television, display, etc. For example, a DAC in a camcorder may be used to drive the signal to a television set.

Referring now toFIG. 1, a conventional DAC110coupled to a receiver120is shown. DAC110may be a DAC that belongs to a handheld electronic device, e.g., a camcorder. It is appreciated that the receiver may be any load that may be coupled to the DAC110. For example, the receiver120may be a television set, a display, etc. Various standards may be employed by DACs. For example, one standard is a composite standard that uses one DAC coupled to the receiver120. Another standard is an S-video standard that uses two DACs coupled to the receiver120. Finally, a VGA standard may be used that uses three DACs coupled to the receiver120.

Unfortunately, DACs consume a considerable amount of power. As a result, in order to conserve power, it is desirable to turn off the clock to the DAC110when the DAC110is not coupled to the load, e.g., receiver120.

Unfortunately, detection of load disconnection, e.g., receiver120, is complicated to automate because the DAC110is generally controlled by the content, e.g., video content. Since load detection is manual, without user interaction the DAC keeps operating and consuming power even after it is disconnected from the load. For example, a DAC within a camcorder continues its operation and consumption of power even after it is disconnected from a television set. As a result, the manual process is not only tedious by requiring user interaction but it is power inefficient because without manual intervention by the user the DAC keep consuming power even though the load may no longer be connected.

SUMMARY

Accordingly, a need has arisen for improving power efficiency of electronic devices that use DACs by automatically detecting load disconnection. As such, when load disconnection is detected, the clock to the DAC may be turned off to save power. It will become apparent to those skilled in the art after reading the detailed description of the present invention that the embodiments of the present invention satisfy the above mentioned needs.

In one embodiment of the present invention, a first reference signal that may be known apriori can be used for load detection. For example, the first reference signal may be used for an invisible portion of a frame. The DAC receives the first reference signal and outputs a signal that is based on the first reference signal. The output of the DAC may have two known values depending on whether the load is coupled to the DAC, e.g., one value when the load is coupled and another value when the load is not coupled to the DAC. Thus, the output signal may be used for detecting whether the load is uncoupled from the DAC.

As a result, when the output of the DAC is compared to a known second reference signal, e.g., voltage value when the load is coupled and/or value when the load is uncoupled, it can be determined whether the load, e.g., receiver, television, display, etc. is coupled to the DAC. If it is determined that the load is uncoupled from the DAC, the clocking signal to the DAC may be turned off. Thus, the DAC no longer consumes power when the load is uncoupled, thereby saving power.

More specifically, an embodiment of the present invention pertains to a system for automatic load detection. The system includes a display controller generating a control signal. A selector may be used to select pixel data or a first reference signal, wherein the selection is responsive to the control signal.

The system may further include the DAC that receives a selection by the selector and outputs a signal, wherein the output signal has a first detectable value when the first reference signal is selected and the load is coupled to the DAC, and wherein the output signal has a second detectable value when the first reference signal is selected and the load is uncoupled from the DAC. The DAC is operable to convert the pixel data to analog signal, wherein the analog signal is operable to be displayed on a display. According to one embodiment, the value of the output signal changes between the first detectable value and the second detectable value due to a change in impedance when the load is uncoupled from the DAC.

The system may further include a comparator that compares the output signal to a second reference signal and outputting a comparison signal, wherein the comparison signal has a third value when the output signal has the first detectable value, and wherein the comparison signal has a fourth value when the output signal has the second detectable value. The system further includes a deactivating component operable to turn off a clock to the DAC when the comparison signal has said fourth value.

The embodiments include the above and wherein, the control signal is the line number for a pixel line being processed. The selector may be a multiplexer.

According to one embodiment, the selector selects the first reference signal when the control signal corresponds to the line number for a pixel line that is not visible. The selector may select the first reference signal when the control signal corresponds to the not visible portion of the line number for a pixel line that includes visible and not visible portions. The deactivating component may be selected from a group consisting of a status register and a state machine.

DETAILED DESCRIPTION

Improved Power Management Using Automatic Load/Unload Detection of DAC

Referring now toFIG. 2, an exemplary renderable frame200in accordance with one embodiment of the present invention is shown. In general, renderable frames contain various lines that may include visible and invisible portions. The visible portion refers to a portion of the frame that is visible to the end-user. The invisible portion on the other hand refers to a portion of the frame that is invisible to the end-user.

The renderable frame200comprises a visible frame portion210. Moreover, the renderable frame200includes lines that are invisible to the user. For example, renderable frame200includes invisible lines220on the top and the bottom of the frame200. For example, in NTSC analog television system lines19and20may be invisible to the user, but it is not limited thereto.

It is appreciated that some lines within the frame200may include both visible and invisible portions. For example, on the same line that the visible frame210is rendered, invisible lines may be present, e.g., back porch240and front porch230. In general, front porch230refers to invisible lines to the right of the visible frame210portion and the back porch240refers to invisible lines to the left of the visible frame portion210.

It is appreciated that the location of invisible lines220, visible frame210, invisible front porch230and invisible back porch240are exemplary and are not intended to limit the scope of the present invention. For example, the frame200may comprise only invisible front porch230portion and the visible frame210portion, without having the top and the bottom invisible lines220and without having the invisible back porch240portion. As such, the location of visible lines and invisible lines or portions of visible and/or invisible lines within a frame is not intended to limit the scope of the present invention.

As presented and discussed above, load detection e.g., load disconnection, is complicated to automate because the DAC is controlled by the video content. Moreover, the DAC cannot be driven by a user-defined input during the active area of the video display, e.g., visible portion of the display, since it is visible to the user. Thus, the invisible portion of the frame, e.g., invisible lines220, front porch230and/or back porch240, etc., may be used for load detection.

Referring now toFIG. 3, an exemplary system300for automatic load detection in accordance with one embodiment of the present invention is shown. In one embodiment, the exemplary system300comprises a graphical processing unit (GPU)310, a display controller320, a selector such as a multiplexer330, a DAC340, a load350, a comparator360and a status register370.

In one embodiment of the present invention, a first reference signal312that may be known apriori can be used for load detection. For example, the first reference signal312may be used for invisible portion of a frame, e.g., pixels for invisible lines220, front porch230, back porch240, or any combination thereof. The DAC340receives the first reference signal312and outputs a signal342that is based on the first reference signal312. The output of the DAC340may have two known values depending on whether the load350is coupled to the DAC340, e.g., one value when the load350is coupled and another value when the load350is not coupled to the DAC340. Thus, the output signal342may be used for detecting whether the load350is uncoupled from the DAC340.

As a result, when the output of the DAC340is compared to a known second reference signal362, e.g., voltage value when the load is coupled and/or value when the load is uncoupled, it can be determined whether the load350, e.g., receiver, television, display, etc. is coupled to the DAC340. If it is determined that the load350is uncoupled from the DAC340, the clocking signal to the DAC340may be turned off. Thus, DAC340no longer consumes power when the load350is uncoupled, thereby saving power. The operation of the system300is described in more detail below.

The GPU310is operable to process graphical information and produce pixel data operable for rendering on a display, e.g., television, display, etc. The GPU310may be coupled to the display controller320. It is appreciated that the GPU310may be integrated within a central processing unit (CPU) or it may be separate from the CPU.

In one embodiment, the display controller320generates a control signal. In one example, the control signal is the line number for the frame, e.g., line19of the frame. As a result, in one exemplary embodiment the display controller320may include a counter (not shown) for counting the lines and updating the line number for the line being processed. In one embodiment, the control signal may correspond to raster information for a pixel being processed. The raster information may include coordinates of the pixel. The control signal is sent to the multiplexer330.

The multiplexer330receives various input signals along with the control signal from the display controller320. Input signals include a first reference signal312and pixel data. The first reference signal312may be a known signal, e.g., having a known digital value. The pixel data is data that is to be rendered by the load350, e.g., a display, a television set, receiver, etc.

As discussed above, the invisible portion of the frame, e.g., invisible lines220, front porch230and/or back porch240, any combination thereof, etc., may be used for load detection. Thus, the multiplexer330is designed to select the first reference signal312when the raster information corresponds to invisible portion of the frame that is being processed and to select the pixel data when the visible portion, e.g., visible frame210, of the frame is being processed.

If the invisible portion, e.g., pixels in the back porch240, front porch230, invisible lines220, etc., are being processed, the multiplexer330selects the first reference signal312based on the control signal received from the display controller320. The first reference signal312is sent to the DAC340. The DAC340may or may not change the value of the received first reference signal312. The DAC340may then output signal342.

In one embodiment, when the load350is coupled to the DAC340, the output342signal has a first detectable value. In comparison, when the load350is uncoupled from the DAC340, the output342signal has a second detectable value. The first and the second detectable values are based on the impedance of the load350when coupled to the DAC340and when uncoupled from the DAC340. For example, the first detectable value may be a detectable voltage when the load350is coupled to the DAC340and the second detectable value may be a detectable voltage when the load350is uncoupled from the DAC340. It is appreciated that the detectable values are not limited to voltage values. Thus, detectable values based on a detectable voltage is exemplary and should not be construed as limiting the scope of the present invention. For example, a detectable current may be used instead but it is not limited thereto.

Apriori knowledge of the first detectable value and the second detectable value may be used to determine whether the load350is coupled or uncoupled from the DAC340. For example, the comparator360may be used to compare the output342signal with the reference362signal. In one example, the reference362signal may have a value equal to the first detectable value. Thus, when the reference362signal and the output342signal have the same value, it is determined that the load350is coupled to the DAC340. Similarly, when the reference signal362and the output342signal have different values, e.g., the output342signal has a second detectable value, it is determined that the load350is uncoupled from the DAC340.

It is appreciated that the value of the reference signal362may be changed to any known value depending on the design requirement. For example, the reference362signal may have a value equal to the second detectable value. As a result, when the reference362signal and the output342signal are compared and have the same value, it is determined that the load350is uncoupled from the DAC340. Similarly, when the reference362signal and the output342signal are compared and have different values, e.g., the output signal342has a first detectable value, it is determined that the load350is coupled to the DAC340.

It is further appreciated that the reference signal362may be chosen to have a value different than that of the first detectable and the second detectable value. For example, the reference signal362may be any value and comparing the reference signal362may result in an offset value that can be accordingly used to determine whether the load350is coupled to the DAC340in a similar manner. Thus, the value of the reference signal362presented above are exemplary and are not intended to limit the scope of the present invention.

The comparator360outputs a comparison signal that as discussed above indicates whether the load350is coupled to the DAC340or uncoupled from the DAC340. When the comparison signal determines that the load350is uncoupled from the DAC340, the status register370may generate a deactivation signal based on a programmable instruction. The deactivation signal may disable/deactivate the sending of the clock signal to the DAC340and/or turn off the clock signal to the DAC340. As a result, the DAC340no longer consumes power when the load350is uncoupled from the DAC340. It is appreciated that a state machine (not shown) or other similar components may be used instead of the status register370or in conjunction with the status register370to turn off the clock and/or deactivate/disable the sending of the clock signal to the DAC340.

It is appreciated that in one embodiment, to save power, the DAC logic may be turned off in addition and/or instead of turning off the clocking signal. Moreover, it is appreciated that in one embodiment in order to save power, the power is cut to the power rail that is associated with a particular logic partition of the DAC340.

In contrast, when the visible portion, e.g., visible frame210, is being processed, the multiplexer330selects the pixel data based on the control signal received from the display controller320. The pixel data is then sent to the DAC340. The DAC340converts the pixel data from a digital format into analog signal operable for rendering by the load350, e.g., television set, display, receiver, etc. It is appreciated that the output of the DAC340may be similarly processed by the comparator360, as discussed above.

It is appreciated that, the load350may comprise various components. In one exemplary embodiment, the load350may be coupled to the DAC340via a pad352, a plug and a 75 ohm impedance that is used as a terminal logic. The load may comprise a video decoder354, a 75 ohm coax cable and an alternative current (AC) coupling. It is further appreciated that 75 ohm impedance may be used by the receiver in order to have a proper matching with the 75 ohm coax cable. 75 ohm coax cable and 75 ohm impedance matching is exemplary and should not be construed as limiting the scope of the present invention. For example, a 50 ohm impedance may be used instead. Since the impedance of the load350effects the first and the second detectable values for the output signal342, the reference signal362may be chosen by considering the known impedance of the load350.

Referring now toFIG. 4, an exemplary flow diagram400for automatic load detection in accordance with one embodiment of the present invention is shown. At step410, a control signal is generated by the display controller320. The display controller320may generate the control signal based on the signal received from the GPU310. In one example, the control signal may be the line number for the pixel line within the frame that is being processed, e.g., line19of an NTSC television frame. In one embodiment, the control signal may correspond to raster information for a pixel being processed. The raster information may include coordinates of the pixel.

At step420, in response to the control signal received, the multiplexer330may select a first reference signal312or pixel data. In one example, the pixel data are processed digital data operable for rendering. The first reference signal312on the other hand may be a signal that may be known apriori, e.g., a known digital value that may be a voltage value.

It is appreciated that the first reference signal312may be selected when the control signal corresponds to the raster information for a pixel that is not visible. For example, the first reference signal312may be selected when the control signal corresponds to the invisible lines220. The first signal may also be selected when the control signal corresponds to the invisible portion of the pixel line that comprises visible and invisible portions, e.g., front porch230and/or back porch240, to name a few.

The selected signal may be sent to the DAC340. If the selected signal is pixel data, the DAC340converts pixel data from digital to analog format that is operable for rendering by the load, e.g., television set, display, etc. If the selected signal is the first reference signal312, the DAC340may or may not change its value. At step430, the DAC340outputs the resultant signal.

At step440, the output signal from the DAC340may be compared to a second reference signal362. When the multiplexer330selects the first reference signal312, the output of the DAC340may be a first detectable value or a second detectable value based on whether the load350is coupled to the DAC340. In other words, the impedance of the load350affects the detectable value of the output from the DAC340.

It is appreciated that the second reference signal362may be any value. For example, the second reference signal362may be a value corresponding to when the load350is coupled to the DAC340. Similarly, the second reference signal362may be a value when the load350is not coupled to the DAC340. As a result, the comparator360may determine whether the load350is coupled to the DAC340or whether the load350is uncoupled from the DAC340. It is appreciated that the value of the second reference signal362discussed above is exemplary and should not be construed as limiting the scope of the present invention.

At step450, the comparator360outputs a comparison signal which is the result of the comparison. Accordingly, the comparison signal having a third value may indicate that the load350is coupled to the DAC340and a fourth value may indicate that the load350is uncoupled from the DAC340.

At step460, when the comparison signal determines that the load350is uncoupled from the DAC340, a signal may be generated, e.g., deactivation/disabling signal, to turn off the clock to the DAC340. Turning off the clock to the DAC340may be performed by a state machine and/or a status register, as discussed above.

As a result, load detection is automatically determined. Thus, it is automatically determined whether the load350is coupled to the DAC340. Accordingly, when the load350is not coupled to the DAC340, the DAC340can be turned off to prevent wasting power. Turning off the DAC340may be via turning off the clock or disabling the clock to the DAC340or by other means discussed above. Thus, the power consumption of the DAC340is reduced when the load350is not coupled to the DAC340, thereby saving power when not in use.

In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is, and is intended by the applicants to be, the invention is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.