Devices having an integrated, capacitive touch-screen, such as mobile phones, handheld navigation devices, and portable music players are increasingly popular. When such a device is plugged-in to an AC power source, such as to charge a battery of the device and/or to power the device, common mode noise may be generated that causes display jitter and/or is sensed as a false touch input to a capacitive touch-screen of the device. One possible solution to reduce common mode noise is to utilize a common mode inductor. However, the expense associated with such a component can increase the production cost of a device to a point that this is not a viable solution. Another conventional solution is to utilize a Y-capacitor. However, this component solution has been determined to increase leakage current, which may give a user a feeling of an electrical shock when the user makes direct electrical contact with a device that is connected to a charger.
Embodiments of a dynamic impedance circuit are described with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:
In embodiments of a dynamic impedance circuit, a power circuit of a device charges and/or powers the device when the device is connected to a power source. For example, a mobile phone can be plugged-in to an AC power source to charge a battery of the device and/or to power the device. A dynamic impedance circuit is coupled to the power circuit of the device and to the power source. The dynamic impedance circuit operates with low impedance, and alternatively, operates with high impedance responsive to an increased voltage across the dynamic impedance circuit, such as when a chassis of the device is coupled to ground.
Various implementations of dynamic impedance circuits are described herein. Generally, a dynamic impedance circuit exhibits low impedance when a voltage across the circuit is minimal or decreases, and current is then increased. Alternatively, the dynamic impedance circuit exhibits high impedance when the voltage across the circuit increases, and current is then decreased. The voltage across a dynamic impedance circuit increases when a chassis of a device is capacitively coupled to ground, such as when user contact with the chassis of the device capacitively couples the device to ground. A dynamic impedance circuit can reduce current flow, such as leakage current, at least when the dynamic impedance circuit operates with high impedance. The dynamic impedance circuit can also attenuate common mode noise at least when the dynamic impedance circuit operates with low impedance.
In embodiments, a dynamic impedance circuit can be implemented with circuit components that include varactor diodes, junction-gate field effect transistors (JFETs), or a negative resistor. Optionally, a Y-capacitor may be coupled in series with any of the dynamic impedance circuits to electrically isolate a device from a power source in an event the power circuit in the device fails.
While features and concepts of the described dynamic impedance circuits can be implemented in any number of different devices, systems, and/or configurations, embodiments of a dynamic impedance circuit are described in the context of the following example devices, systems, and methods.
The example system 100 also includes a dynamic impedance circuit 110 that is coupled to the switching power source 108 and to the device power circuit 106. The dynamic impedance circuit may be implemented as a circuit of the powered device 102, such as part of the device power circuit along with an integrated power supply. The dynamic impedance circuit may also be integrated in a system-on-chip (SoC) with other components and/or logic of the device. Alternatively, the dynamic impedance circuit may be implemented as a circuit of the switching power source, such as part of a power supply that is external to the powered device. In embodiments, the dynamic impedance circuit is implemented to operate with low impedance in a first operational state. The dynamic impedance circuit is also implemented to operate with high impedance in a second operational state, such as when a voltage across the dynamic impedance circuit increases, which is also the voltage difference between the device power circuit and the switching power source.
The example device 200 includes a dynamic impedance circuit 214, which is coupled to the switching power supply 206 and to the device power circuit 204. Specifically, the dynamic impedance circuit is coupled between the transformer primary 208 of the switching power supply and the transformer secondary 210 of the switching power supply. The powered device may include the dynamic impedance circuit as an independent circuit or integrated in an SoC with other components and/or logic of the device. As described with reference to the dynamic impedance circuit shown in
The representation 300 also includes a dynamic impedance circuit 308 and an optional Y-capacitor 310 coupled in series with the circuit. The Y-capacitor may be included to electrically isolate the device 302 from a power source in an event the power circuit in the device fails. Similar to the powered device shown in
The dynamic impedance circuit 308 operates with high impedance when a voltage across the circuit increases, which is also a voltage difference between the device and the power source. The dynamic impedance circuit exhibits negative impedance and an increase in the voltage across the dynamic impedance circuit results in a decrease in current through the circuit, such as a decrease in leakage current. The voltage across the dynamic impedance circuit increases when user contact at 312 and/or 314 with a chassis 316 of the device capacitively couples the device to ground, as represented by capacitors 318, 320 in the illustration. The chassis of the device is conductive and, either directly or indirectly (including inductively), is coupled to the device power circuit. A high-frequency component of the common mode noise that may otherwise cause display jitter is shunted to ground when the device is capacitively coupled to ground. The capacitance between the device and ground is relatively large and the common mode noise, such as generated from a charging device, has little to no impact on the function of the capacitive touch-screen of the device. The chassis of a device may also be referred to as a housing portion, an outer casing, a shell, or other similar structures that define a form factor of the device and that a user contacts when holding the device.
The representation 400 also includes a dynamic impedance circuit 408 and an optional Y-capacitor 410 coupled in series with the circuit. The Y-capacitor may be included to electrically isolate the device 402 from a power source in an event the power circuit in the device fails. Similar to the powered device shown in
The dynamic impedance circuit 408 operates with low impedance, and is illustrated as a short circuit merely to represent the low impedance. When the circuit is implemented as any of the various dynamic impedance circuits described herein, such as with reference to
The representation 500 also includes a switching power supply 508, a dynamic impedance circuit 510 operating with a low impedance, and an optional Y-capacitor 512 coupled in series with the dynamic impedance circuit. The switching power supply, dynamic impedance circuit, and Y-capacitor may all be implemented as described with reference to the respective components shown in
An alternative dynamic impedance circuit 612 is implemented with multiple configurations of the circuit components 614 (the JFETs) of the dynamic impedance circuit 608 connected in series. As described with reference to the device shown in
An alternative dynamic impedance circuit 712 is implemented as a four-varactor diode circuit, and another alternative dynamic impedance circuit 714 is implemented as a two-varactor diode circuit. As described with reference to the device shown in
As described with reference to the device shown in
The results chart 900 illustrates that the leakage current 904, when user contact with the chassis of the device capacitively couples the device to ground, decreases as a dynamic impedance circuit is implemented with more varactor diodes. A decrease in leakage current is illustrated as an improvement in the results chart. In this instance, the leakage current 904 is better when a dynamic impedance circuit is implemented with a six-varactor diode circuit, such as the dynamic impedance circuit 708 shown in
The results chart 902 illustrates that the low-frequency common mode noise 906, when the chassis of the device is not coupled to ground, decreases as a dynamic impedance circuit is implemented with more varactor diodes. A decrease in common mode noise is illustrated as an improvement in the results chart. In this instance, the low-frequency common mode noise 906 is better when a dynamic impedance circuit is implemented with a six-varactor diode circuit, such as the dynamic impedance circuit 708 shown in
Alternatively, the low-frequency common mode noise 906 increases as a dynamic impedance circuit is implemented with more varactor diodes when the chassis of the device is coupled to ground, as shown in the results chart 900. In this instance, the low-frequency common mode noise 906 is better at 914 when a dynamic impedance circuit is implemented with a two-varactor diode circuit, such as the dynamic impedance circuit 714 shown in
The results chart 902 illustrates that the high-frequency common mode noise 908, when the chassis of the device is not coupled to ground, improves as a dynamic impedance circuit is implemented with more varactor diodes. The results chart 900 illustrates that the high-frequency common mode noise 908, when the chassis of the device is coupled to ground, remains approximately constant at 916 as a dynamic impedance circuit is implemented with more varactor diodes. Note that the high-frequency common mode noise 908 is overall decreased when the chassis of the device is coupled to ground as compared to when the chassis of the device is not coupled to ground.
The results chart 1000 also illustrates that when the chassis of a device is coupled to ground, such as when user contact with the chassis of the device capacitively couples the device to ground, the impedance at 1008 of the JFET implementation 1002 is greater than the impedance at 1010 of the simple Y-capacitor implementation 1006. The greater impedance at 1008 of the JFET implementation 1002 suppresses leakage current.
At block 1102, a device coupled to a switching power supply is powered and/or charged. For example, the power circuit 106 (
At block 1104, a voltage is varied between the device and the switching power supply across a dynamic impedance circuit, which is coupled to the device and to the switching power supply. For example, the voltage across the dynamic impedance circuit 110 that is coupled to the switching power source 108 and to the device power circuit 106 varies, such as when the chassis of the device is capacitively coupled to ground as shown in
At block 1106, an impedance is varied responsive to varying the voltage across the dynamic impedance circuit. For example, the impedance is increased (at block 1106) as a voltage difference between the switching power supply and the device power circuit increases (at block 1104) responsive to a chassis of the device being coupled to ground, such as when user contact with the chassis of the device capacitively couples the device to ground. As described with reference to
At block 1108, a determination is made as to whether there is an alternate path to ground, such as when user contact with the chassis of the device capacitively couples the device to ground via the user. If there is not an alternate path to ground (i.e., “no” from block 1108), then at block 1110, the dynamic impedance circuit operates with a low impedance. For example, the dynamic impedance circuit 408 (
Further, at block 1112, common mode noise is attenuated through the dynamic impedance circuit when the dynamic impedance circuit operates with low impedance. For example, the dynamic impedance circuit 408 attenuates common mode noise at least when the circuit operates with low impedance. The method can then continue at block 1108 to determine whether there is an alternate path to ground when the device is coupled to a switching power supply at block 1102.
If there is an alternate path to ground (i.e., “yes” from block 1108), then at block 1114, the dynamic impedance circuit operates with high impedance. For example, the dynamic impedance circuit 308 operates with high impedance responsive to the voltage across the dynamic impedance circuit increasing, such as when user contact with the chassis 316 of the device capacitively couples the device to ground. Further, at block 1116, current flow is reduced through the dynamic impedance circuit when the dynamic impedance circuit operates with high impedance. For example, current through the dynamic impedance circuit 308 is reduced when the voltage across the circuit increases. The method can then continue at block 1108 to determine whether there is an alternate path to ground while the device is coupled to a switching power supply at block 1102.
The device 1200 includes communication devices 1202 that enable wired and/or wireless communication of device data 1204, such as received data, data that is being received, data scheduled for broadcast, data packets of the data, etc. The device also includes one or more data inputs 1206 via which any type of data, media content, and/or inputs can be received, such as user-selectable inputs, messages, music, television content, recorded video content, and any other type of audio, video, and/or image data received from any content and/or data source.
The device 1200 also includes communication interfaces 1208, such as any one or more of a serial, parallel, network, or wireless interface. The communication interfaces provide a connection and/or communication links between the device and a communication network by which other electronic, computing, and communication devices communicate data with the device.
The device 1200 includes one or more processors 1210 (e.g., any of microprocessors, controllers, and the like), which process computer-executable instructions to control operation of the device. Alternatively or in addition, the device can be implemented with any one or combination of software, hardware, firmware, or fixed logic circuitry that is implemented in connection with processing and control circuits, which are generally identified at 1212.
In embodiments, the device 1200 can be implemented with a power circuit 1214 and a dynamic impedance circuit 1216 as described with reference to any the previous
The device 1200 also includes one or more memory devices 1218 that enable data storage, examples of which include random access memory (RAM), non-volatile memory (e.g., read-only memory (ROM), flash memory, EPROM, EEPROM, etc.), and a disk storage device. A disk storage device may be implemented as any type of magnetic or optical storage device, such as a hard disk drive, a recordable and/or rewriteable disc, any type of a digital versatile disc (DVD), and the like. The device 1200 may also include a mass storage media device.
A memory device 1218 provides data storage mechanisms to store the device data 1204, other types of information and/or data, and various device applications 1220. For example, an operating system 1222 can be maintained as a software application with a memory device and executed on processors 1210. The device applications may also include a device manager, such as any form of a control application, software application, signal-processing and control module, code that is native to a particular device, a hardware abstraction layer for a particular device, and so on.
The device 1200 also includes an audio and/or video processing system 1224 that generates audio data for an audio system 1226 and/or generates display data for a display system 1228. The audio system and/or the display system may include any devices that process, display, and/or otherwise render audio, video, display, and/or image data. Display data and audio signals can be communicated to an audio device and/or to a display device via an RF (radio frequency) link, S-video link, composite video link, component video link, DVI (digital video interface), analog audio connection, or other similar communication link. In implementations, the audio system and/or the display system are external components to the device. Alternatively, the audio system and/or the display system are integrated components of the example device, such as an integrated capacitive touch-screen.
Although embodiments of a dynamic impedance circuit have been described in language specific to features and/or methods, the subject of the appended claims is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as example implementations of dynamic impedance circuits.
Number | Date | Country | |
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Parent | PCT/CN2010/078690 | Nov 2010 | US |
Child | 13892165 | US |