Power management in a computer

0001The invention relates to power management in a computer.

0002Power management is an important consideration in the design of modern personal computers. For effective power management, modern personal computers are designed to enter a low power mode after a certain period of inactivity. In order for a personal computer to be in compliance with the "Energy Star" industry standard, the computer must consume less than thirty watts of power in the low power mode.

0003A typical power management scheme for a personal computer is shown in prior art Fig. 1. A personal computer 1 is provided with a central processing unit (CPU) 2, a hard drive 3, an audio board 4, and a power supply 5. The computer 1 is connected to a monitor 6 for display purposes. The computer 1 is also provided with a power management integrated circuit (PMIC) 7 which controls transition into and out of low power mode. The PMIC 7 acts as a "watchdog", and powers down auxiliary components of the personal computer after a certain period of inactivity. This is achieved by issuing a signal to open one or more switches 8, resulting in removal of supply power from the auxiliary components, which in the example of Fig. 1 include the monitor 6, hard drive 3 and audio board 4. The PMIC 7 is provided to control the low power mode instead of vesting this responsibility in the CPU because the CPU itself requires a great deal of power. Therefore, when transition to low power mode occurs, the PMIC issues a signal to the CPU 2 causing the CPU to enter a low power mode. The PMIC 7 then remains active to detect activity such as entry on a keyboard or movement of a mouse (not shown), at which time PMIC 7 will "wake up" the CPU 2 and reactivate the auxiliary components of the computer.

0004In some aspects, the invention relates to an apparatus for power management in a computer, comprising: circuitry configured to assert a power down signal in connection with entering a low power mode; an audio amplifier having a mute input; a switch connected to selectively supply power to the audio amplifier; and a power down circuit responsive to the power down signal and connected to activate the mute input and subsequently open the switch when the power down signal is asserted by the power down circuit.

0005In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the circuitry is configured to de-assert the power down signal in connection with exiting the low power mode, and wherein the power down circuit closes the switch and deactivates the mute input when the power down signal is de-asserted. In some embodiments, the invention relates to the apparatus for power management in a computer, wherein a delay of at least 20 ms occurs between activation of the mute input and opening of the switch.

0006In some embodiments, the invention relates to the apparatus for power management in a computer, wherein a delay of at least 20 ms occurs between deactivation of the mute input and closing of the switch.

0007In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the power down signal is a step function, and the power down circuit comprises means for converting the step function into a ramp function.

0008In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the power down circuit generates a mute signal when a first voltage level is reached along the ramp function and for generating a delayed power down signal when a second voltage is reached along the ramp function.

0009In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the power down signal is a step function, and wherein the power down circuit comprises: a delay circuit arranged to convert the step function into a ramp function; a reference voltage circuit configured to supply a first reference voltage and a second reference voltage; a first comparator arranged to generate a mute signal when the ramp function reaches the first reference voltage; and a second comparator arranged to generate a delayed power down signal when the ramp function reaches the second reference voltage.

0010In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the delay circuit comprises a resistor and a capacitor.

0011In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the reference voltage circuit comprises a voltage divider.

0012In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the first reference voltage is greater than said second reference voltage.

0013In some embodiments, the invention relates to the apparatus for power management in a computer, wherein the first reference voltage is equal to approximately 2.4 volts, and the second reference voltage is equal to approximately 0.5 volts.

0014In some aspects, the invention relates to an apparatus for power management in a computer, comprising: circuitry configured to control entry into and exit from a low power mode; an audio amplifier having a mute input and a power input; a switch connected to selectively supply power to the power input; and an integrated circuit connected to the circuitry via a bus and connected to the mute input and the switch; wherein when the circuitry effects entry into the low power mode the integrated circuit activates the mute input and subsequently opens the switch, and when the circuitry effects exit from said low power mode, said integrated circuit closes the switch and subsequently deactivates the mute input.

0015In some embodiments, the invention relates to the apparatus for power management in a computer, and further comprises a delay between activation of the mute input and opening of the switch and between closing of the switch and deactivation of the mute input is at least 20ms.

0016In some embodiments, the invention relates to an apparatus for power management in a computer, wherein the integrated circuit comprises an application specific integrated circuit.

0017In some aspects, the invention relates to a method for power management in a computer, comprising of steps of: in response to a low power mode signal, applying a mute signal to an audio amplifier to engage a mute function; and after a first delay following application of the mute signal, disconnecting power from said audio amplifier.

0018In some embodiments, the invention relates to the method for power management in a computer, further comprising the steps of: in response to deactivation of the low power mode signal, re-connecting power to the audio amplifier; and after a second delay following the re-connecting of power to the audio amplifier, deactivating the mute signal to disengage the mute function.

0019In some embodiments, the invention relates to the method for power management in a computer, wherein the first delay is at least 20 ms.

0020In some embodiments, the invention relates to the method for power management in a computer, wherein the second delay is at least 20 ms.

0021Advantages of the invention may include one or more of the following. Pops and clicks are reduced during transitions to and from low power mode. Muting of the audio amplifier is achieved without requiring significant additional power consumption. Other advantages and features will become apparent from the following description and from the claims. <ul id="ul0001" list-style="none" compact="compact"><li>FIG. 1 is a block diagram showing a known power management scheme in a personal computer;</li><li>FIG. 2 is a block diagram in accordance with one embodiment of the invention;</li><li>FIG. 3 is a schematic diagram in accordance with the embodiment of FIG. 2;</li><li>FIG. 4A is a timing diagram illustrating the power down sequence in accordance with the embodiment of FIG. 3;</li><li>FIG. 4B is a timing diagram illustrating the power up sequence in accordance with the embodiment of FIG. 3;</li><li>FIG. 5 is a block diagram in accordance with another embodiment of the invention;</li><li>FIG. 6A is a flow chart of the power down sequence in accordance with the embodiment of FIG. 5; and</li><li>FIG. 6B is a flow chart of the power up sequence in accordance with the embodiment of FIG. 5.</li></ul>

0022Referring the FIG. 2, a mute signal and a delayed power down signal (PD') are derived from the power down signal (PD) issued by the PMIC. PMIC 7 issues the PD signal on line 13 to a power down circuit 15. In a manner described in more detail below, the power down circuit 15 generates the mute signal on line 17 and the delayed power down signal PD' on line 19. The delayed power down signal PD' is applied to a switch 21 that is arranged to selectively connect or disconnect a +12 volt supply on line 23 to V_CC pin 25 of an audio amp 27. Switch 21 may be any type of conventional switch, including an N-channel power transistor or relay.

0023In the conventional power management scheme shown in Fig. 1, the PD signal from PMIC 7 is applied directly to the switch 8. Thus, when the PD signal is activated, switch 8 is opened and power is cut to the auxiliary components. This direct cutting of the power causes difficulties with respect to the audio board 4. Specifically, direct cutting of power to the audio amplifier on the audio board 4 causes clicks and pops to be heard through the speakers of the personal computer, which result from noises and transients within the audio amp. In the present invention as shown in Fig. 2, the PD signal is delayed to allow the mute signal to be applied to a mute pin 29 of the audio amp 27 prior to power being disconnected by the switch 21. Thus, the mute function is activated within the audio amp at the time switch 21 is opened, preventing clicks or pops from being heard through speakers 31.

0024During the power up sequence, the process is reversed. The mute signal on line 17 is deactivated after the delayed power down signal PD' on line 19 closes switch 21. Therefore, the audio amp remains muted until after power to the audio amp has been reestablished and all transients and noise have dissipated.

0025FIG. 3 shows power down circuit 15 in detail. The PD signal is applied to power down circuit 15 on line 13. The PD signal is active low, meaning that the low power mode is entered when the PD signal switches from a high state to a low state. Within the parameters relevant to this invention, the transition of the PD signal from high to low occurs instantaneously, i.e., as a step function. Resistor 33 and capacitor 35 on the input side of power down circuit 15 establish a time constant which converts the step function of the PD signal into a ramp function at point 37. This ramp function (PD(37)) is illustrated in the timing diagram of FIG. 4A. The values of resistor 33 and capacitor 35 can be chosen to produce a desired slope of the ramp function in accordance with well known engineering principles. Typical values would include 20kΩ for resistor 33 and 1µF for capacitor 35.

0026The ramped PD signal at point 37 is applied to the positive input of two comparators 39, 41. The comparators may be any conventional comparator, such as the LM339. Reference voltages for the comparators are supplied from a +5 volt supply provided via line 43, which supplies a voltage divider comprising resistors 45, 47, and 49. The values of resistors 45, 47 and 49 are chosen to establish a first voltage V_OH applied to the negative input of comparator 39 and a second voltage V_OL applied to the negative input of comparator 41. As illustrated in FIG. 4A, voltages V_OH and V_OL are chosen to be points along the PD(37) ramp function, e.g., V_OH is set to 2.4 volts, and V_OL is set to 0.5 volts. The time τ along the PD(37) ramp function is chosen to be of sufficient duration to allow dissipation of any transients or noise in the audio amp 27, e.g., at least 20ms. As the signal PD(37) ramps down from 5 volts, the output from comparator 39, which is the mute signal on line 17, is initially high because the voltage on the positive input of the comparator 39 is higher than the voltage on the negative input. When the signal PD(37) reaches the level of V_OH, the output of comparator 39 goes low. At this time, the output of comparator 41, which is the delayed power down signal PD' on line 19, is still high because the voltage on the positive input of comparator 41 is still higher than the voltage on the negative input. After the time τ, however, the voltage of PD(37) reaches V_OL, and the output of comparator 41 switches from high to low. Shortly thereafter, all of signals PD(37), the mute signal, and the PD' signal are at zero volts.

0027Referring back to FIG. 2, it is now apparent that when the PMIC issues the PD signal to enter low power mode, power down circuit 15 first generates the mute signal on line 17 to activate the mute function of the audio amp. A period of time τ later, which is sufficient to allow the mute function to become fully engaged and all noise and transients to dissipate, the delayed power down signal PD' is issued to open switch 21 and remove power from terminal 25 of the audio amp.

0028Referring now to FIG. 4B, the opposite sequence occurs when leaving the power down mode. In this case, the CPU exits low power mode by switching PD signal on line 13 from low to high. As a result of the delay caused by resistor 33 and capacitor 35, this is converted into an upward ramp function PD(37) as shown in FIG. 4B. When signal PD(37) reaches the level V_OL, the delayed power down signal PD' output by comparator 41 switches from low to high, thus closing switch 21 and re-connecting power to the audio amp 27. A period of time τ later, after all noise and transients have dissipated within the audio amp 27, the level V_OH is reached, and the mute signal output by comparator 39 switches from low to high, thus disengaging the mute function of the audio amp 27. As a result, no undesirable sounds are emitted from speakers 31 in either the power down or the power up sequence.

0029An alternate embodiment of the invention is illustrated in FIG. 5. In this embodiment, the mute and PD' signals are issued under software control by the CPU 11. This embodiment of the invention requires the use of two general purpose input/output (GPIO) ports of an application specific integrated circuit (ASIC) 51 connected to CPU 11 via a bus 53. Software within CPU 11 causes ASIC 51 to issue the mute signal from GPIO₀ 53 and the delayed PD' signal from GPIO₁ 55 at the same timings described above with reference to FIGs. 4A and 4B. The end result is the same as the embodiment of FIG. 1. Namely, during the power down sequence, CPU 11 first causes ASIC 51 to issue the mute signal at port GPIO₀ to activate the mute function of audio amp 27. After the period of time τ has elapsed, the CPU 11 causes ASIC 51 to issue the PD' signal at port GPIO₁, which opens switch 21 and removes power from the audio amp 27. During the power up sequence, the reverse sequence occurs in the manner described above with reference to FIG. 4B.

0030FIG. 6A is a flow chart illustrating the software executed by CPU 11 during the power down sequence. In step ST101, the CPU 11 must keep the ASIC 51 active, i.e., make sure that the ASIC itself is not powered down when the low power mode is entered. In step ST103, CPU 11 writes to GPIO₀, causing the mute signal to go from high to low and the mute function of audio amp 27 to be activated. In step ST105, the CPU 11 sets an internal timer, which is a conventional feature of the CPU and is not shown in the drawings, equal to the desired time delay τ. In step ST107, the CPU 11 waits until the timer has expired. When it has, CPU 11 writes to GPIO₁ in ST109, causing the PD' signal to go low and thus switch 21 to be opened.

0031FIG. 6B is a flow chart illustrating the software executed by CPU 11 during the power up sequence. In ST111, the CPU 11 makes sure that the output of GPIO₀ remains active, i.e., that the mute function of audio amp 27 remains engaged. In ST113, the output of GPIO₁ is de-asserted, causing the PD' signal to go high and switch 21 to be closed. The internal timer of the CPU 11 is set to the time τ in state ST115, and in state ST117 the CPU waits for the timer to expire. When the timer has expired, GPIO₀ is de-asserted in state ST119, thus deactivating the mute function of audio amp 27.

0032Specific embodiments of the invention have been described above with reference to the accompanying figures. However, the invention is not limited to the specific embodiments, and rather is limited only by the scope of the appended claims.