WO2006133594A1

WO2006133594A1 - Circuit and process for power management

Info

Publication number: WO2006133594A1
Application number: PCT/CN2005/000612
Authority: WO
Inventors: James Y. Gao; Shaofeng Liang
Original assignee: Apexone Microelectronics Inc.
Priority date: 2005-04-30
Filing date: 2005-04-30
Publication date: 2006-12-21
Also published as: CN100451920C; WO2006133594A8; CN101076771A

Abstract

An electronic device (10) has a power management circuit (20) that switches the device (10) on and off in response to whether a user is touching the device (10). The power management circuit (20) includes a conductor plate (214) underlying a dielectric outer casing (216) of'the device (10). When a user touches the device (10), the user's body and the conductor plate (214) forms a sensing capacitor (213). The sensing capacitor (213) and a reference capacitor (223) are periodically charged and discharged. A comparison circuit element (230) compares the voltage differences between the two capacitors (213, 223) to determine whether a user is touching the device (10) and generates a control signal to switch the device (10) on and off accordingly.

Description

CIRCUIT AND PROCESS FOR POWER MANAGEMENT

Field of the Invention

The present invention relates, in general, to power management system and, more particularly, to a system and a method for managing the operation and power consumption in electronic devices.

Background of the Invention

Power management in portable electronic devices, e.g., for portable computers, personal data assistants (PDAs), tablet computers, cellular phones, and wireless computer peripherals, etc., is becoming increasingly important as the demand for longer intervals between battery replacement or recharging has increased. For example, a wireless cursor control (pointing) device such as a computer mouse or trackball device includes a battery power source within the device and the provision of a wireless data link, e.g., an infrared or RF transmitter/receiver pair. Without effective power management, continuous operation of such wireless device will rapidly deplete the limited battery power of the device, thus requiring frequent battery replacement or recharging. Many electronic devices are often turned on for ready usability but left idle for significant periods of time. This presents an opportunity to reduce depletion of battery power through the use of reduced power modes. Efficient power management can significantly increase the life of the battery power between replacement or recharge. Motion sensing provides a way detecting the use of a device, e.g., a wireless mouse, in the power management. The motion sensing can be achieved through ball and associated encoder wheels or optical tracking. In response to sensing the mouse being moved, a power system enters a working mode for data transmission and processing. If the mouse is not moved for a predetermined period, e.g., five seconds, the power management system enters a power saving mode with reduced power consumption and signal process speed. After a longer time interval, e.g., ten seconds, of the mouse not being moved, the power management may enter a hibernation state with even lower power consumption. In the hibernation state, the signal processing circuit in the mouse is in a sleep state with minimum power consumption. Upon detecting the mouse being moved, the power management system enters the working state and wakes up the signal processing circuit. If the mouse is not moved for a prolonged period, e.g., twenty seconds, the power management system switches off the signal processing circuit and enters an off state. During the off state, only the motion sensing circuit in the power management system is active and consumes electrical energy.

Capacitance sensing provides another way detecting the use of mouse. For example, U.S. Patent No. 6,661,410 discloses a capacitance sensing power management system that includes a scoop capacitor and a bucket capacitor coupled to a reference voltage source. When an operator touches the mouse with his/her hand or other body parts, The operator becomes another plate of the scoop capacitor. The power management system selectively charges the scoop capacitor and the bucket capacitor. A charge transfer between the two capacitors varies the charge on the bucket capacitor in relation to the capacitance of the scoop capacitor. The charge on the bucket capacitor is then compared with a threshold value to determine whether the operator is touching the mouse. Like the power management system with motion sensing, the capacitance sensing power management system typically has multiple states, e.g., working state, power saving state, hibernation state, off state.

During the off state, the motion sensing or the capacitance sensing circuit is the only active component of the device. For a device, e.g., a wireless mouse, that is idle for significant periods of time, the power consumption of the sensing circuit is essential for the power efficiency of the device. The state of art motion sensing and capacitance sensing circuits generally has an idle current of about one hundred microamperes. Furthermore, the motion and capacitance sensing in the existing art are usually slower than desirable. Programming the power saving mode and hibernation mode in addition to the working and off modes provides a comprise between the power saving and fast response speed. In the power saving mode or the hibernation mode, the signal processing circuit is not completely switched off. Therefore, the device responds to human commands faster in the power saving or hibernation mode than in the off mode. Accordingly it would be advantageous to have a device with a simple and reliable power management circuit and a process for effectively managing the power consumption of the device. It is desirable for the device to have small idle power consumption. It is also desirable for the power management circuit to have a short response time in changing the device from the idle state to the working state. It is of further advantage if the device can immediately enter the power efficient idle state when the device is not in use. Brief Description of the Drawings

Figure 1 is a block diagram illustrating a device having a power management circuit in accordance with the present invention;

Figure 2 is a schematic diagram illustrating a power management circuit in accordance with the present invention; and

Figure 3 schematically shows a portion of a device and illustrates the formation of a sensing capacitor in a power management circuit in accordance with the present invention.

Detailed Description of Various Embodiments

Various embodiments of the present invention are described herein below with reference to the figures, in which elements of similar structures or functions are represented by like reference numerals throughout the figures. It should be noted that the figures are only intended to facilitate the description of the preferred embodiments of the present invention. They are not intended as an exhaustive description of the present invention or as a limitation on the scope of the present invention. Furthermore, the figures are not necessarily drawn to scales.

Figure 1 is a block diagram illustrating a device 10 having a power management circuit 20 in accordance with the present invention. Device 10 can be any kind of electronic device that has power management capabilities. According the present invention, power management circuit 20 is especially beneficial if device 10 is a device that operates on battery power. By way of example, device 10 may be a personal digital assistant (PDA), a wireless remote control device, a portable audio device, a wireless data transmission and process device, etc. In accordance with a specific embodiment of the present invention, device 10 is described hearing after as a wireless mouse for use with a computer.

Wireless mouse device 10 includes a battery 11 and a data processing element 12. Data processing element 12 may include a digital signal processor, a digital to analog converter, a digital to analog converter, a radio frequency (RF) or infrared (IF) signal transceiver, etc. Battery 11 provides power for the operations of data processing element 12. Power management circuit 20 is connected to a control terminal 14 of data processing element 12 for transmitting a control signal to data processing element 12. In accordance with a preferred embodiment of the present invention, data processing element 12 has an on state and an off state. The control signal transmitted from power management circuit 20 to control terminal 14 switches data processing element 12 between the on and off states.

Figure 2 is a schematic diagram illustrating power management circuit 20 in accordance with the present invention. Power management circuit 20 has an output terminal 245 coupled to control terminal 14 of data processing element 12 in device 10 (shown in Fig. 1). In response to whether device 10 is in use or not, power management circuit 20 generates a control signal at output terminal 245 to switch data processing element 12 between on and off states, thereby preserving the power efficiency of device 10.

Power management circuit 20 includes a clock signal generator 202. In accordance with the present invention, clock signal generator 202 may include any kind of oscillating signal generator. For example, a resistor-capacitor (RC) oscillator, a crystal oscillator, or the like, can serve as clock signal generator 202. In accordance with various embodiments of the present invention, the frequency of clock signal may be in a range between several kilohertz and several megahertz. However, higher or lower clock signal frequencies also fall into the scope of the present invention. The clock signal of clock signal generator 202 is transmitted to the control terminals of switches 212 and 222 in power management circuit 20. In accordance with a preferred embodiment of the present invention, switches 212 and 222 are field effect transistors (FETs) or bipolar junction transistors (BJTs) and the clock signal is transmitted to the gate electrodes of the FETs or the base electrodes of the BJTs. Switches 212 and 222 are coupled in parallel with capacitors 213 and 223, respectively. Power management circuit 20 also includes current sources 211 and 221. Current source 211 is coupled in series with the parallel combination of switch 212 and sensing capacitor 213. Likewise, current source 221 is serially coupled with the parallel combination of switch 222 and capacitor 223. In a specific embodiment of the present invention, the currents generated by current sources 211 and 221 are substantially equal to each other. Current sources 211 and 221 charge capacitors 213 and 223, respectively, when switches 212 and 222 are open. When switches 212 and 222 are closed, the currents from current sources 211 and 221 bypass capacitors 213 and 223 and flow to ground 205. Furthermore, closed switches 212 and 222 discharge capacitors 213 and 223. In accordance with the present invention, capacitor 213 in power management circuit 20 senses whether device 10 is in use. Circuit schematic diagram Fig. 2 shows that capacitor 213 includes two plates 214 and 215. A piece of conductor serves as one plate 214, which is also referred to as a sensing plate, of capacitor 213. The physical structure of power management circuit 20 includes only one plate 214 of capacitor 213. When device 10 is in use, a user's body serves as another plate 215 of capacitor 213. Figure 3 schematically shows a portion of device 10 and illustrates the formation of capacitor 213. Device 10 includes a dielectric layer 216 overlying and in contact with plate 214 of capacitor 213. By way of example, dielectric layer 216 is a part of the casing, housing, or outer covering of device 10. Although the casing of a device may include various kinds of materials, e.g., plastic, metal, etc, the portion of the casing overlying sensing capacitor plate 214, i.e., layer 216 shown in Fig. 3, is preferably made of an insulating and dielectric material. Plastic is a commonly used material for casing device 10 because it is dielectric, inexpensive, and can be easily made with various shapes and colors. Figure 3 shows sensing capacitor plate 214 as a flat plate in accordance with an embodiment of the present invention. This is not intended as a limitation on the scope of the present invention. In accordance with the present invention, sensing capacitor plate 214 of capacitor 213 can have different shapes and sizes. In addition, plate 214 can include more than one pieces of conductors electrically coupled to each other. For example, plate 214 can include one or more pieces of conductor conformal to the shape of outer covering of device 10. When a user touches outer covering of device 10, a portion of the user's body, e.g., a finger as shown in Fig. 3, comes into contact with the casing of device 10 overlying sensing capacitor plate 214. If the contact area has an overlap with dielectric layer 216 overlying plate 214, that portion of the user's body functions as the other plate 215 of capacitor 213. The rest of the user's body functions as ground 205 (shown in Fig. 2).

It should be noted that when a user touches device 10, the user's body functions as a conductor. In accordance with the present invention, the scope of a user touching device 10 is not limited to the user's body in direct contact with device 10. It covers any conducting object in contact with dielectric layer 216 and functions as plate 215 in sensing capacitor 213.

Referring back to Fig. 2, power management circuit 20 also includes a comparison module 230 for comparing the voltage difference between capacitors 213 and 223. In accordance with a preferred embodiment of the present invention, comparison module 230 includes a differential amplifier 234. Capacitors 213 and 223 are connected to a first input 231 and a second input 232, respectively, of differential amplifier 234. An output 235 of differential amplifier 234 is coupled to a first plate of a capacitor 238, which is also referred to as an integration capacitor. A second plate of capacitor 238 is connected to ground 205. The first plate of capacitor 238 is also coupled to a first input of a comparator 244 in comparison module 230. A second input of comparator 244 is coupled for receiving a reference voltage 243. An output of comparator 244 serves as an output of comparison module 230 and is coupled to output terminal 245 of power management circuit 20.

It should be noted that the structure of comparison module 230 is not limited to that described herein above and shown in Fig. 2. In accordance with the present invention, comparison module 230 can be any circuit element that is capable of comparing the voltage pulse signals at inputs 231 and 232 and generating an output signal indicating which voltage pulse signal is higher.

In operation, clock signal generator 202 periodically turns switches 212 and 222 on and off at a rate of the clock signal frequency. In accordance with a preferred embodiment of the present invention, the on and off states of switches 212 and 222 are substantially synchronous to each other. Therefore, capacitors 213 and 223 are charged and discharged periodically and substantially simultaneously. The capacitance of capacitor 213, which is also referred to as a sensing capacitor, varies in response to whether device 10 is in contact with a user. On the other hand, the capacitance of capacitor 223, which is also referred to as a reference capacitor, is substantially constant. Comparison module 230 compares the capacitances of sensing capacitor 213 and reference capacitor 223 to determine whether device 10 is in use and generates the control signal to switch data processing element 12 between the on and off states accordingly.

When a user does not touch device 10, the body of the user, which functions as plate 215 of capacitor 213 in Fig. 3, is far away from plate 214. In addition, plate 215 is separated from plate 214 not only by dielectric layer 216 by also by an air gap. Because of the low dielectric constant of the air, the capacitance of sensing capacitor 213 is significantly smaller than that of reference capacitor 223. During the clock signal phases in which switches 212 and 222 are open, the voltage at input 231 of differential amplifier 234 rises faster than that at input 232. In response to the higher voltage at input 231, which is, by way of example, a non-inverting input, differential amplifier 234 generates a high voltage at output 235. During the clock signal phases in which switches 212 and 222 are closed, the voltages at both inputs 231 and 232 return to ground voltage level. Therefore, differential amplifier 234 generates a high voltage pulse signal at output 235. The frequency of the pulses is equal to that at which capacitors 213 and 223 are charged and discharged. Capacitor 238 integrates the high voltage pulse signal from differential amplifier 235. Specifically, the high voltage pulses at output 235 of differential amplifier 234 repeatedly charge capacitor 238, thereby generating a high voltage at the first input of comparator 244. Comparator 244 compares the voltage at its first input with reference voltage 243 at its second input. In response to the voltage at the first input, which is, by way of the example, is an inverting input, being higher than reference voltage 243 at the second input, which, by way of example, is a non-inverting input, comparator 244 generates a low voltage signal at output terminal 245 of power management circuit 20. The low voltage signal, which, by way of example, has a binary value of zero, is transmitted to control terminal 14 of data process element 12. In response to the binary zero at control terminal 14, data processing circuit 12 enters an off state with substantially zero power consumption.

When a user touches device 10, the body of the user, which functions as plate 215 of capacitor 213, is in contact with the casing of device 10, which functions as dielectric layer 216 in capacitor 213, as shown in Fig. 3. Because of the proximity of plate 215 to plate 214 and the dielectric constant of dielectric layer 216, the capacitance of sensing capacitor 213 is significantly larger than the capacitance of sensing capacitor 213 when the user does not touch device 10. In accordance with a preferred embodiment, the capacitance of sensing capacitor 213 is larger than that of reference capacitor 223 when the user touches device 10. During the clock signal phases in which switches 212 and 222 are open, the voltage at input 231 of differential amplifier 234 rises slower than that at input 232. In response to the lower voltage at input 231, which is, by way of example, a non-inverting input, differential amplifier 234 generates a low voltage at output 235. During the clock signal phases in which switches 212 and 222 are closed, the voltages at both inputs 231 and 232 return to ground voltage level. Therefore, differential amplifier 234 generates a low voltage pulse signal at output 235. The frequency of the pulses is equal to that at which capacitors 213 and 223 are charged and discharged. Capacitor 238 integrates the low voltage pulse signal from differential amplifier 234. Specifically, the low voltage pulses at output 235 of differential amplifier 234 repeatedly discharge capacitor 238 and generate a low voltage at the first input of comparator 244. Comparator 244 compares the voltage at its first input with reference voltage 243 at its second input. In response to the voltage at the first input, which is, by way of the example, is an inverting input, being lower than reference voltage 243 at the second input, which, by way of example, is a non-inverting input, comparator 244 generates a high voltage signal at output terminal 245 of power management circuit 20. The high voltage signal, which, by way of example, has a binary value of one, is transmitted to control terminal 14 of data process element 12 (shown in Fig. 1) and switches data processing circuit 12 to its on state or working state.

Accordingly, device 10 is in an off state when it is not in contact with a user. During the off state, power management circuit 20 is the only part of device 10 that consumes power. The performance and power consumption of power management circuit 20 depend on the frequency of the clock signal that controls switches 212 and 222 for charging and discharging sensing capacitor 213 and reference capacitor 223, respectively. A high frequency generally results in a high performance and high power consumption. In accordance with various embodiments of the present invention, the clock signal has a frequency ranging from a few hundred hertz to a several mega-hertz. In a preferred embodiment, the frequency of the clock signal is about a few kilo-hertz. Clock signal generator 202 usually includes an oscillator, which may be a simple resistor-capacitor (RC) oscillator, a voltage controlled oscillator, a current controlled oscillator, a crystal oscillator, etc. In a preferred embodiment, clock signal generator 202 includes an on-chip RC oscillator because of its simplicity and power efficiency. The performance and power consumption of power management circuit 20 also depend on the characteristics of current sources 211 and 221, sensing capacitor 213 and reference capacitor 223, differential amplifier 234, integration capacitor 238, reference voltage 243, and comparator 244. For example, a small capacitance for integration capacitor 238 will have a short charging and discharging time, which results in a fast response time for power management circuit 20. Small capacitance for integration capacitor 238 also results in smaller power consumption of power management circuit 20. In addition, large current sources 211 and 221 will result in fast charging rates of sensing capacitor 213 and reference capacitor 223. In accordance with the present invention, a circuit designer can adjust the parameters of various devices in power management circuit 20 to achieve a desirable response time and performance.

The capacitance of sensing capacitor 213 is substantially zero when a user does not touch device 10 and serve as plate 215 in contact with dielectric layer 216 as shown in Fig. 3. When a user touches device 10, the capacitance of sensing capacitor 213 is determined by the thickness and dielectric constant of dielectric layer 216 and the area of plate 214. Dielectric layer 216 is generally made of a plastic material. For a user's body to form plate 215 of sensing capacitor 213, the user must touch device 10 at an area directly over plate 214. In order to have to be able to switch on signal processing element 12 by touching various points on the casing of device 10, sensing capacitor 213 may include multiple conductor plates at different positions under the outer casing of device 10. In this embodiment, the user's body touching device 10 and the conductor plate directly under the contact point form sensing capacitor 213. In an alternative embodiment, a piece of conducting material conformal to and in contact with the outer casing of device 10 forms plate 214 of sensing capacitor 213.

By now it should be appreciated that a circuit and a process for efficiently managing an electronic device have been provided. In accordance with the present invention, a power management module in the device switches on functional circuitry in the device in response to a user touching the device and switches off the functional circuitry in response to the user not touching the device. Therefore, the device is in an off state when not in use. Compared with existing power management circuits, the power management circuit is simple and fast and power efficient. Because of its fast response time, there is usually no need to for functional circuitry to have multiple power saving states, e.g., stand-by state, hibernation state, sleeping state, etc. Two states, on and off, are sufficient for the effective and efficient operation of the device. When the device is not in use, the power management circuit is the only portion of device that consumes power. A power management circuit in accordance with the present invention has a small current, e.g., in the range of several microamperes to several tens of microamperes. In the off state, functional circuitry in the device can be completely switched off and therefore consumes substantially no power.

While specific embodiments of the present invention have been described herein above, they are not intended as limitations on the scope of the invention. The present invention encompasses those modifications and variations of the described embodiments that are obvious to those skilled in the art. For example, although the specification describes the power management circuit and process in conjunction with a wireless mouse, the present invention encompasses power management and control in various electronic devices. Also by way of example, the functional circuitry in the device is described having two states, on and off. This is not intended as a limitation on the scope of the present invention. In accordance with the present invention, the can many any number of states. Furthermore, the power management circuit and process described herein above are not limited to the application of power management. In accordance with the present invention, they can be easily modified and used as a control circuit in other applications such as, for example, generating control signals for controlling the functions of a circuit element.

Claims

1. A control circuit for controlling a circuit element, comprising: a first current source; a conductor plate coupled to said first current source; a dielectric layer overlying said conductor plate; a first switch having a first electrode coupled to said conductor plate and a second electrode coupled to a ground; a second current source; a capacitor having a first electrode coupled to said second current source and a second electrode coupled to the ground; a second switch having a first electrode coupled to the first electrode of said capacitor and a second electrode coupled to the second electrode of said capacitor; and a comparison module having a first input coupled to said conductor plate, a second input coupled to the first electrode of said capacitor, and an output coupled to a control terminal of the circuit element.

2. The control circuit of claim 1 , each of said first switch and said second switch having a control electrode coupled to receive a clock signal.

3. The control circuit of claim 1, in response to a user touching said dielectric layer, the user and said conductor plate forming a sensing capacitor.

4. The control circuit of claim 1, said comparison module including a differential amplifier having a first input coupled to said conductor plate, a second input coupled to the first electrode of said capacitor, and an output coupled to the output of said comparison module.

5. The control circuit of claim 4, said comparison module further including a comparator having a first input coupled to the output of said differential amplifier, a second input coupled to a reference voltage level, and an output coupled to the output of said comparison module.

6. The control circuit of claim 5, said comparison module further including an integrating capacitor having a first electrode coupled to the output of said differential amplifier and a second electrode coupled to the ground.

7. An electronic device, comprising: an outer casing made of a dielectric material; a functional circuit having a control terminal that receives a control signal to switch said functional circuit between a first state and a second state in response to the control signal; and a power management circuit, including: a first current source and a second current source; a conductor plate underlying at least a portion of said outer casing and coupled to said first current source; a capacitor coupled between said second current source and the ground; a first switch coupled between said conductor plate and a ground; a second switch in a parallel combination with said capacitor; a clock signal generator coupled to control electrodes of said first switch and said second switch; and a comparison module having a first input coupled to said conductor plate, a second input coupled to said capacitor, and an output coupled to said control terminal of said functional circuit, wherein said comparison module generates a first control signal in response to a first voltage pulse at the first input being higher than a second voltage pulse at the second input and generates a second control signal in response to the first voltage pulse being lower than the second voltage pulse.

8. The electronic device of claim 7, wherein: in response to an electrically conducting object in contact with said outer casing overlying said conductor plate, the electrically conducting object and said conductor plate form a sensing capacitor having a capacitance larger than a capacitance of said capacitor; and in response to no electrically conducting object in contact with said outer casing overlying said conductor plate, said sensing capacitor has a capacitance smaller than the capacitance of said capacitor.

9. The electronic device of claim 8, wherein: in response to the capacitance of said sensing capacitor being larger than the capacitance of said capacitor, said comparison module generates a first control signal to switch said function circuit to an on state; and in response to the capacitance of said sensing capacitor smaller than the capacitance of said capacitor, said comparison module generates a second control signal to switch said function circuit to an off state.

10. The electronic device of claim 7, wherein said comparison module includes: a differential amplifier having a first input coupled to said conductor plate, a second input coupled said capacitor, and an output coupled to the output of said comparison module; and an integrating capacitor coupled between the output of said differential amplifier and the ground.

11. The electronic device of claim 9, wherein said comparison module further includes a comparator having a first input coupled to the output of said differential amplifier, a second input coupled to a reference voltage level, and an output coupled to the output of said comparison module.

12. The electronic device of claim 7, wherein said conductor plate includes a plurality of conductor plates positioned under a plural portions of said outer casing and coupled to each other.

13. The electronic device of claim 7, wherein said conductor plate includes a conducting plate conformal to said outer casing.

14. The electronic device of claim 7, wherein said clock signal generator includes an on- chip resistor-capacitor oscillator.

15. A power management process for a device, comprising: providing a reference capacitor having a reference capacitance; providing a sensing capacitor comprised of a conductor plate underlying a dielectric outer casing of the device and having a first capacitance smaller than the reference capacitance in response to no user touching the device and a second capacitance larger than the reference capacitance in response to a user touching the dielectric outer casing of the device; comparing the capacitance of the sensing capacitor with the reference capacitance; in response to the sensing capacitor having the first capacitance smaller than the reference capacitance, switching a functional circuit of the device to an off state; and in response to the sensing capacitor having the second capacitance larger than the reference capacitance, switching the functional circuit to an on state.

16. The power management process of claim 15, comparing the capacitance of the sensing capacitor and the reference capacitance comprising: charging the sensing capacitor and the reference capacitor; and comparing a voltage level of the conductor plate with a voltage across the reference capacitor.

17. The power management process of claim 15, comparing the capacitance of the sensing capacitor and the reference capacitance comprising: periodically charging and discharging the sensing capacitor and the reference capacitor; comparing a first pulse signal at the conductor plate and a second pulse signal at the reference capacitor; charging an integration capacitor in response to a first relationship between the first pulse signal and the second pulse signal; and discharging an integration capacitor in response to a second relationship between the first pulse signal and the second pulse signal.

18. The power management process of claim 17, comparing the capacitance of the sensing capacitor and the reference capacitance further comprising comparing a voltage at the integration capacitor with a reference voltage level.

19. The power management process of claim 18 : comparing the capacitance of the sensing capacitor and the reference capacitance further comprising: generating a first control signal in response to the voltage at the integration capacitor being higher than the reference voltage level; and generating a second control signal in response to the voltage at the integration capacitor being lower than the reference voltage level.

20. The power management process of claim 19: switching a functional circuit of the device to an off state including switching off the functional circuit in response to the first control signal; and switching the functional circuit to an on state including switching on the functional circuit in response to the second control signal.