Systems and methods for dynamic current scaling of analog functions in an imager

According to the invention, a system for dynamically scaling bias current on an imaging system is disclosed. In the invention an image sensor capable of producing at least a two-dimensional image and capable of at least two modes of operation is equipped with a control unit. The control unit determines a digital output for each of the modes of operation of the imaging system and outputs the digital outputs to a converter. The converter converts the digital output from the control unit to a bias current and provides this output to an analog and or mixed signal circuit associated with the imaging system that has operating characteristics that may be varied by the application of different bias currents.

BACKGROUND OF THE DISCLOSURE

This disclosure relates in general to reducing power consumption associated with portable devices and, more specifically, but not by way of limitation, to reducing power consumption of analog and/or mixed signal circuits associated with imaging systems.

The advent of portable electronic devices such as personal digital assistants (“PDAs”), wireless telephones, camera phones, digital cameras and camcorders, and the like, has brought about a need to limit power consumption by the portable devices so as-to increase battery life. Techniques, such as Dynamic Voltage Scaling (“DVS”), have been developed to reduce power consumption of digital circuits in portable electronic devices. However, DVS does not address power consumption by analog or mixed signal circuits. Therefore, because of the desirableness of reducing power consumption, there is a need in the art for methods and systems of reducing power consumption by analog and mixed signal circuits in portable electronic devices.

In 2004 almost 10 million camera equipped wireless phones were sold in the United States. And it is expected that as many as 28 million camera equipped wireless phones may be sold in 2005. Further, it is reported that worldwide sales of camera phones will exceed 100 million units in 2005. Reducing power consumption by the image sensor systems (cameras) in the camera phones is highly desirable to reduce power consumption and, as a result, increase battery life of camera phones to make them more attractive to consumers.

In the appended figures, similar components and/or features may have the same reference label.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention provide methods and systems for dynamically scaling bias currents applied to analog and/or mixed signal circuits in response to changes in the required characteristics of the analog and/or mixed signal circuits. More specifically, but not by way of limitation, embodiments of the present invention relate in general to methods and systems for scaling bias currents for analog and/or mixed signal circuits in an image sensor device in response to changes in the mode of operation of the image sensor device.

Certain embodiments of the present invention may provide systems and methods for dynamic scaling bias currents that may be applied to analog and/or mixed signal circuits in image sensor devices. For purposes of this application, dynamic scaling of bias currents applied to analog or mixed signal circuits is described with reference to an image sensor device. However, the systems and methods for dynamic bias current scaling disclosed in this application may be applied to many other devices incorporating analog and/or mixed signal circuits, such as wireless phones, PDAs, camcorders, mobile media devices, and the like. The term “image sensing device” may apply to any electronic device capable of producing, at least, a two-dimensional image, such as a camera phone, digital camera, digital video camera, a scanner, and the like.

Scaling of the bias current applied to analog and/or mixed signal circuits in response to changes in the desired operation of the image sensing device may provide for reduction in the consumption of power by the image sensor device. In certain embodiments of the present invention, bias currents applied to analog and/or mixed signal circuits may be reduced when the analog and/or mixed signal circuit is operating at a frequency lower than the circuit's maximum frequency. In some embodiments of the present invention, bias currents applied to analog and/or mixed signal circuits may be reduced when the analog and/or mixed signal circuit is producing signals of lower quality. Merely by way of example, a digital control unit may be used to scale the bias current or currents that may be applied to the analog or mixed signal circuits.

For purposes of this specification, an image sensor device may comprise of an image sensor array and certain related circuits for operating and producing an output image from the image sensor array. The image sensor may be a one-dimensional column or a two-dimensional array of pixels and the pixels on the two-dimensional array may be considered as rows and columns. Outputs from the pixels may be applied to various circuits and processed to produce an output signal from the image sensor device. In certain aspects, circuits associated with the image sensor array may provide for the amplification and analog to digital conversion of the signals produced by the pixels of the image sensor array. Embodiments of the present invention may be used with any type of image sensor, e.g., a charge coupled device (“CCD”) or a complementary metal oxide semiconductor (“CMOS”) image sensor.

For purposes of this written description of the present invention, the term “bias current” shall be given its ordinary meaning in the art and may refer to a current that is applied to an analog or mixed signal component to control the operating characteristics of the analog or mixed signal component. As persons of skill in the art can appreciate, for a given operation characteristic of an analog or mixed signal circuit, such as the frequency of operation of the transconductance operational amplifier or the signal quality deliverable from an analog to digital; converter, a bias current may be applied to the analog and or mixed signal device so that the component functions with the desired characteristics. Further, for the analog and/or mixed signal component to operate with the desired characteristics there is an associated minimum bias current that, in general, needs to be applied to the analog and/or mixed signal device. Application of a bias current lower than the minimum bias current may not enable the analog and/or mixed signal component to operate with the required operating characteristics in some cases. Further, application of a bias current greater than the minimum current may provide for the operation of the analog and/or mixed signal component in the desired manner, but may result in the unnecessary consumption of current.

As persons of skill in the art are can appreciate, power consumption is related to the current flowing on a device and the power consumption of a device, including an image sensor device, is related to and will increase as a function of the sum of the various bias currents applied to analog and/or mixed signal components in the image sensor device. As such, it is possible to reduce the power consumption of an image sensor device by reducing the magnitude of the bias current or bias currents applied to the various analog and mixed signal circuits in the image sensor device.

FIG. 1is a flow diagram depicting an embodiment of a method of dynamically scaling bias current for analog and/or mixed signal circuits in an image sensor device. In step110, a mode of operation of an image sensor device100is selected. As discussed above, an image sensor device may comprise and image sensor array and various circuits to process the image output from the image sensor array, including analog and/or mixed circuit signal circuits, such as amplifiers, comparators, analog-to-digital converters, and the like. In embodiments of the present invention, the mode of operation of the image sensor device100may refer to the resolution of the image to be produced by the image sensor device100, the frame rate of a video image to be produced by the image sensor device100, frequency of operation, or the like. Merely by way of example, in camera phones a user may often select from three or more modes of operation of the image sensor device (camera). In one embodiment, the user of a camera phone may select modes of operation of the image sensor device producing images of 640×480, 320×240, or 160×120 pixels in still image operation and 128×96 and 176×144 in video operation. Other resolutions to scale between are possible for other embodiments.

In certain embodiments of the present invention, the operation characteristics of analog and mixed signal circuits in the image sensor device100may be altered depending upon the mode of operation of the image sensor device100as a whole. Merely by way of example, when the image sensor device100is set to produce high resolution images, high resolution of high frame rate video images, or the like, the analog and mixed signal circuits of the image sensor device100—such as comparators, amplifiers, ADCs, and the like—may be set to perform at a high end of their capabilities. As such, the bias currents to the analog and mixed signal circuits of the image sensor device100may be set to a high or maximum value to provide that the analog and/or mixed signal devices are producing the necessary operating characteristics, i.e., are operating at the correct frequency and/or are outputting the correct signal quality. Further, merely by way of example, when the image sensor device100is set to provide lower resolution images, lower frequency video, or the like, the analog and/or mixed signal circuits associated with the device—such as amplifiers, comparators, ADCs, and the like—may operate at a lower frequency and/or output a lower signal quality and, as a result, may use a lower bias current.

In step120, biasing current requirements of analog and/or mixed signal devices associated with the image sensor device100may be processed according to the selected mode of operation of the image sensor device100. In accordance with embodiments of the present invention, processing of bias current requirements may be performed by a microcontroller or state machine. Processing may involve determining the applicable bias currents to apply to the analog and/or mixed signal circuits in the image device so as to operate the image sensor device100in accordance with the selected mode. This processing may involve selecting a preprogrammed bias current to provide to the analog and/or mixed signal circuit in order to operate the analog an/or mixed signal circuit with the operating characteristics required by the selected mode of operation. Once the mode of operation of the image sensor device100has been determined, in step130the processor may output a digital output corresponding to a magnitude of the bias current to be applied to an analog and or mixed signal circuit in order for the analog or mixed signal circuit to operate in the manner required by the selected mode.

In certain embodiments, processing the bias current requirements for analog and/or mixed signal circuits associated with the image sensor device100may require processing the minimum bias current that may be applied to the analog and/or mixed signal circuits that will provide the operating characteristics from the analog and/or mixed signal circuits necessary for the selected mode of operation of the image sensor device. In this way, in certain aspects of the present invention, the bias current to be applied to one or more of the analog and/or mixed signal circuits may be controlled by the processor. In further aspects of the present invention, the digital output may be scaled up or down by the processor in accordance with the selected mode.

In an embodiment of the present invention, as depicted in step140, the outputted digital signal may be communicated to a digital to analog converter. In some aspects of the present invention, the digital to analog converter may convert the digital output from the processor into an analog output. In certain aspects, the digital to analog converter may convert the digital output directly to a current that may be applied to the analog and/or mixed signal circuit. In accordance with an embodiment of the present invention, as depicted in step150, the analog output from the analog to digital converter may be applied to the analog and/or mixed signal circuit.

In some embodiments, the analog output from the digital to analog converter may be a voltage. This voltage may be applied to a current controlling component, such as a transistor, to control the bias current flowing through the component, and the current flowing through the component may then be applied as a biasing current to the analog and/or mixed signal circuit. Merely by way of example, in certain aspects the analog output may be applied to a transistor to control a current flowing through the transistor and the current flowing through the transistor may be the bias current applied to the analog and/or mixed signal circuit.

FIG. 2Ais a simplified block diagram of an embodiment of direct bias current scaling for an analog and/or mixed signal circuit in an image sensing device. In an embodiment of the present invention, a control unit210may control the operation of the analog and/or mixed signal circuits in the image sensor device100. In certain aspects, the control unit210may be a microcontroller or state machine. In the illustrated embodiment of the present invention, when a mode of operation of the image sensor device100is selected—i.e., video or still image, resolution of image, and the like—the control unit210and or a software program associated with the control unit210may determine the bias current or bias currents to be applied to the analog and/or mixed signal circuits of the image sensor device100. In certain embodiments, the control unit210may determine a minimum bias current or be preprogrammed with the bias current to provide to the analog and/or mixed signal circuits in order for the analog and/or mixed signal circuits to operate with the operating characteristics required by the selected mode of operation of the image sensor device100. In certain embodiments, feedback may be provided to the control unit210. Feedback may be provided from the output of the image sensor device100, the output of the analog and/or mixed signal circuits, or the like. In certain aspects, the control unit may change the bias current to be applied to analog and/or mixed signal circuits based upon received feedback.

The bias current to provide to the analog and or mixed signal circuits may be the minimum bias current that will operate the analog and/or mixed signal circuit with the operating characteristics desired for operation of the image sensor device in the selected mode. Alternatively, an error factor may be built into the bias current to provide to the analog and/or mixed signal circuit to provide for such things as operational anomalies in the image sensor device, degradation in the circuits, noise, and the like. In an embodiment of the present invention, the control unit210may be preprogrammed with the bias currents to provide to the analog and/or digital circuits. As such, when a mode of operation is selected for the image sensor device100, the control unit210may provide for the output of a digital output212corresponding to the preprogrammed bias current. In this way, the bias currents applied to the analog and/or digital circuits may be dynamically scaled in response to the changes in the mode of operation of the image sensor. In certain aspects, the value of the preprogrammed bias current to apply to a analog and/or mixed signal circuit may be determined from experimentation with the circuits, recording bias current requirements during operation of the image sensor device, manufacturer specifications, or the like.

The control unit210may output a digital output212corresponding to the bias current to be applied to the analog and/or mixed signal circuit corresponding to the selected mode of operation of the image sensor device100, as processed by the control unit210or an associated software program. In certain embodiments, the control unit210may provide the digital output212to a digital to analog converter220. In certain aspects the analog to digital converter220may be operated by a low-voltage direct current. In some embodiments of the present invention, the analog converter220may convert the digital output212from the control unit210to an analog output222. In certain aspects, the analog to digital converter220may convert the digital output212directly to a current. Further, the analog output222may be passed through an amplifier in order to amplify the analog output.

In certain embodiments, the analog output222may be applied to a circuit230. In an embodiment of the present invention, the analog output222may be the bias current and may be applied directly to the circuit230as a biasing current. In some embodiments, the circuit230may be an analog circuit. In other embodiments, the circuit230may be a mixed signal circuit. In other embodiments, circuit230may be a combination of an analog and mixed signal circuit. Further, in certain aspects circuit230may comprise a single analog or mixed signal component. In other aspects, circuit230may comprise a plurality of components with at least one analog or one mixed signal component. As persons of skill in the art can appreciate, all of the components of the image sensor device100, including the bias current scaling components and digital processing, may be incorporated on a single chip, on the same substrate, or the like. However, in some embodiments of the present invention, components for dynamic current scaling may be external and in communication with the image sensor device100.

FIG. 2Bis a simplified block diagram of an embodiment of indirect bias current scaling for an analog and/or mixed signal circuit in an image sensing device. In an embodiment of the present invention, the control unit210may provide the digital output212for scaling the bias current applied to an analog and/or mixed signal circuit230to the appropriate value for the selected mode of operation of the image sensor device100to the digital to analog converter220. In an embodiment of the present invention, the digital to analog converter220may convert the digital output212to the analog output222. In certain embodiments, the analog output222may be applied to a current controller225. In certain aspects, the control device may be a transistor or the like that is able to control an input current IIN227so as to produce an output bias current IBIAS229. In accordance with some embodiments of the present invention, the analog output222may be applied to the current controller225to scale the output bias current IBIAS229for application to the circuit230. In this way, the control unit210may provide for scaling the output bias current IBIAS229to the required value for operation of the circuit230at the necessary frequency. In some aspects, the analog output222is a voltage that is applied to the current controller225.

Merely by way of example, in certain embodiments of the present invention, a transconductance analog operational amplifier may be used in connection with the image sensor device100, for among other things, amplifying the output from pixels on the sensor array prior to conversion of the pixel output from analog to digital form. In such embodiments, it may be necessary to apply a high bias current across the transconductance analog operational amplifier in modes of operation of the image sensor device100using the transconductance analog operational amplifier to operate at a high frequency, such as to produce high resolution video images. However, a lower bias current may be applied across the transconductance analog operational amplifier when the image sensor device100produces lower resolution video images. In certain embodiments of the present invention, the digital output222may be a voltage and this voltage may be applied as a voltage source to control P-channel transistors in the transconductance operational amplifier. In certain aspects, the P-channel transistors control the bias current flowing through the transconductance operational amplifier and, as such, the output voltage from the digital to analog converter may dynamically scale the bias current in the transconductance operational amplifier.

FIG. 3is a simplified block diagram of an embodiments of bias current scaling of groups of analog and/or mixed signal devices in an image sensor device. The control unit210may process the bias current requirement of analog and/or mixed signal circuits in the image sensor device100for selected modes of operation of the image sensor device100. In many embodiments, control unit210may be in communication with a plurality of analog and/or mixed signal circuits. In some embodiments of the present invention, when a mode of operation of the image sensor device100is selected, control unit210may output a plurality of digital outputs to control and dynamically scale the bias currents applied to the analog and/or mixed signal circuits on the image sensor device100. Merely by way of example,FIG. 3illustrates the control unit210outputting three digital outputs—digitalout1302, digitalout2304and digitalout 3306.

In certain embodiments, digitalout1302, digitalout2304and digitalout3306may be converted to analog outputs—analogout 1322, analogout2324and analogout3336—by digital to analog converter310, digital to analog converter315and digital to analog converter320, respectively. In some embodiments of the present invention, analog and/or mixed signal circuits operating with common bias current requirements may be grouped together. Merely by way of example,FIG. 3illustrates the control unit210in communication, via analog converter310, analog converter315and analog converter320, with three circuit groups—circuit group330, circuit group340and circuit group350. In some aspects, the circuit groups may comprise two or more analog and/or mixed signal circuits. Merely by way of example, as illustrated inFIG. 3, circuit group330comprises of circuits332,334and336. In certain aspects, the circuits332,334and336may all be analog circuits, may all be mixed signal circuits or may be a combination of analog and mixed signal circuits. In some embodiments of the present invention, circuits332,334and336may all have common bias current requirements for different operating modes of the image sensor device100.

In certain embodiments of the present invention, analogout1322may be applied to the circuit group330comprising circuits332,334and336. A common bias current IBIAS335may be applied to the three circuits332,334and336for proper operation of the circuits at the selected mode. In such aspects, as persons of skill in the art can appreciate, analogout1322may be a current with a value corresponding to a multiple of three times the value of IBIAS335so that each to provide that each of the three circuits receives a bias current equal to IBIAS335.

In different embodiments, analogout2314maybe applied to the circuits332,334and336through a current controlling component342. In certain aspects, analogout2314may be a voltage that may be applied to a current controller342and may provide a bias current IBIAS344to a circuit346. In certain embodiments, circuit346may be an analog or mixed signal circuit. A circuit group340may comprise two or more circuits—for example, as illustrated inFIG. 3, circuits346,347and348—in communication with the current controllers342,343and345. In certain aspects, a common voltage may be applied to current controller342, current controller343, and current controller345to provide bias currents to circuit346, circuit347and circuit348, respectively. In certain aspects, the common voltage may provide for the scaling of the bias currents to the analog and/or mixed signal circuits for operation of these circuits at a frequency required by the selected mode of operation of the image sensor device100.

As persons of skill in the art can appreciate, electrical components, such as resistors and transistors, may be added to a first circuit to provide that electrical characteristics of the first circuit match those of a second circuit with different components. In certain aspects, the electrical characteristics of a first circuit may be adjusted to match that of a second circuit receiving the same analog output from the same digital to analog converter to provide that the two circuits may be combined into a circuit group. In certain aspects, when electrical characteristics are appropriately matched, a circuit352receiving a bias current from a current controller355may be in a circuit group350with a circuit354that is driven by a bias current from a digital to analog converter320. The bias currents provided to the circuits of blocks—332,334,335,346,347,348,352,354, and356—in accordance with an embodiment of the present invention, may be dynamically scaled to be just as much as the circuits need to operate at the frequency necessary for the image sensor device100to meet the requirements of the selected mode.

While the principles of the disclosure have been described above in connection with apparatuses and methods, it is to be clearly understood that this description is made way of example and not as limitation on the scope of the invention.