This invention relates to power management and power conservation techniques for personal computers. More particularly, this invention relates to power conservation in the monitor of a personal computer system. In recent years, power management features in personal computers have come into more and more common use, particularly in the very small, battery operated notebook computers. An example of an apparatus for reducing power consumption in a computer system is shown in U.S. Patent No. 4,980,836, which is assigned to the assignee of the present invention and incorporated herein by reference. This apparatus shuts down part of the computer system after a period of inactivity, thus conserving electrical power.

Other ways of reducing power consumption may involve turning off, or slowing down, only certain internal peripheral devices, such as the hard drive. Usually, these methods monitor activity to the peripheral device and, after a certain period of inactivity, shut the peripheral down. Typical power conservation for powering down a hard drive may result in approximately a three percent reduction in power usage by the entire computer system.

In most personal computer systems, the monitor is one of the biggest users of power. However, no one has yet found a way to provide power management features in a computer monitor such as the cathode ray tube (CRT) monitors commonly used with

most desk top personal computers. These monitors are turned on all the time the computer is in use and draw full power the entire time. In a typical system, the monitor may consume three-fourths of all the power. Therefore, considerable power savings may be had if some way to power down the monitor could be accomplished.

In a typical CRT monitor, a filament produces electrons when it becomes very hot. A series of grids and anodes strips the electrons from the filament, accelerates the electrons into a beam and focuses the beam onto a phosphorescent screen. A set of coils deflects the beam onto different areas of the screen to produce an image. The filament, the grids and a first anode form an electron gun. A first grid modulates the number of electrons in the electron beam. A second grid accelerates the electrons through the electron gun. A third grid focuses the electron beam very tightly. The first anode accelerates the electrons even more before they leave the electron gun. Then the coils deflect the beam in the horizontal and vertical directions. Finally, a second anode, a very high voltage device, accelerates the beam a final time before the electrons strike the phosphors on the screen causing an emission of photons. Control circuitry provides the control signals to synchronize the operation of each of these elements so that an image appears on the screen. The deflection coils and the second anode are by far the biggest drain on the power supply.

When a user turns on a monitor, there is usually a several second delay before an image appears on the screen. This delay is due to the need to heat up the heating filament of the electron gun. Although, the deflection coils and the second anode draw the most power, they can be turned on much more quickly than can the heating element. The monitor's control circuitry and the electron gun, except for the filament, can also be turned on very quickly. Therefore, the limiting factor in turning on a monitor is the time needed to heat up the heating filament.

Additionally, the limiting factor in the useful life of a CRT monitor is usually the heating filament. In other words,

keeping the filament hot will eventually cause the filament to wear out, usually before the other elements of the monitor wear out. The ratio of the life of the filament to its temperature is governed by the root mean square distribution. Thus, an increase in the life of a filament will not be linearly proportional to a reduction in the temperature of the filament. Instead, the increase in the life of the filament will be proportional to the square of the reduction in its temperature, so a relatively small change in the temperature of the filament will result in a relatively large change in its useful life.

Also, the ratio of the change in voltage across the filament to the change in temperature of the filament is governed by the root mean square distribution. In this case, the change in voltage is proportional to the square of the change in temperature. Therefore, a reduction in the voltage across the filament will result in a relatively small reduction in the temperature of the filament, which will result in a relatively large increase in its useful life.

Televisions made several years ago powered down every part of the television system when the television was turned off. Then when the television was turned on, several seconds would pass before an image would appear on the screen, because the system had to wait for the heating element to heat up. However, most televisions made today only require a short wait before an image appears. This short time period is due to the fact that most televisions no longer power down every element of the system when the television is turned off. Instead, the new televisions keep the heating element hot even when the system is off. Thus, if a person were to touch the back of a modern television, that person would find the television to be quite warm even though it had been left off for several hours.

Many screen-saver programs already exist for personal computers. These programs usually remove the image on the screen of the monitor after a period of user inactivity and replace the image with a moving image that will not "burn" into screen. One type of screen-saver blanks the screen entirely, so that there is no image at all. When the user touches a key on the keyboard or moves a mouse pointer, thus resuming

activity, the previous image is restored to the screen. However, screen-saver programs do not actually conserve any power in the system. Instead, all of the elements of the monitor remain under full power, even if the screen has been completely blanked out.

Therefore, it is an object of the present invention to provide a power management feature for a personal computer system by powering down selected parts of the system's monitor.

It is an object of the present invention to provide a computer system capable of reducing the power consumption of its display device.

It is a further object to provide a computer display device having a reduced power mode for conserving electrical power.

A standard CRT monitor has several elements that consume power. The present invention powers down some or all of these elements in order to conserve power.

The primary elements of a standard CRT monitor for a computer system inlude a heating filament, control circuitry, a modulator grid, an accelerator grid, a focusing grid, a first accelerating anode, a second accelerating anode, and deflection coils. The invention changes the monitor's power consumption from a normal power mode to a low power mode by turning off the power to all of these elements except the heating filament. The power to the heating filament may remain fully on or slightly reduced.

The computer system sends signals to the monitor to enter the low power mode and subsequently to resume the normal power mode. The signal to enter the low power mode is generated after a period of user inactivity. Thus, the invention monitors the time from the last input from the user through any input device. The signal to resume the normal power mode, on the other hand, is generated by any user activity through any input device.

Figure 1 is a block diagram of a computer system with separate on/off signal wires.

Figure 2 is a block diagram of a computer system with the on/off signals encoded in the video signals.

Figure 3 is a diagram of a computer monitor.

Figure 4 is a schematic diagram of a circuit for providing alternate voltages to a heating filament according to the present invention.

Figure 5 is a perspective view of a computer system incorporating a captive monitor.

A computer system 10 incorporating the present invention is shown in Figure 1. The computer system 10 has a CPU 20, a keyboard 26 and a monitor 40. Keyboard signal wires 28 connect the keyboard 26 to the CPU 20. Monitor control signal wires 22 connect the monitor 40 with the CPU 20. Power mode signal wires 24 send the power mode signals to the monitor 40 from the CPU 20.

A second embodiment of the computer system 10 incorporating the present invention is shown in Figure 2. This computer system 10 has a CPU 20, a keyboard 26 and a monitor 40. Keyboard signal wires 28 connect the keyboard 26 to the CPU 20. Monitor control signal wires 30 with encoded power mode signals connect the CPU 20 with the monitor 40.

Figure 3 shows the elements of a monitor 40 for use in the present invention. The housing 62 of the CRT 64 has a screen 60 and within the housing 62 are the power-consuming elements such as the heating filament 42, modulator grid 44, accelerator grid 46, focusing grid 48, first anode 50, second anode 52 and deflector coils 54. Control Circuitry 56 controls the operation of these elements through control wires 58. The present invention reduces the power consumption of a computer system by turning the power off to selected elements in the monitor. Thus, the system has two power modes when it is powered-on, a low powered-on mode and a normal powered-on mode. In the preferred embodiment, electrical power is turned off to all of the power-consuming elements except the heating filament 42 when the system is in the low powered-on mode. In chis mode, the power to the heating filament 42 remains high, but is reduced slightly. Thus, the system has a normal

powered-on mode in which the power-consuming elements are all turned on and a low powered-on mode in which the selected elements are turned off.

In another embodiment of the invention, the power to the heating filament 42 remains the same, even in the low powered- on mode. In still another embodiment, the power to the heating filament 42 is turned off along with the power to the other power-consuming elements of the monitor 40 in the low powered- on mode. This invention achieves a 65 - 70% reduction in the power consumption by the computer system. By comparison, powering down the hard drive of a personal computer system may achieve only a 3% reduction in power consumption by the computer system. This invention has particular application in a computer system wherein the monitor, or display device, is an integral part of the system, i.e. the display device is "captive" within the system as shown in Fig. 5. Such a captive-monitor computer system may have a computer system 80 with a monitor 82 built onto the CPU housing 84. Many portable computer systems and personal word-processing systems incorporate a captive monitor subsystem without which the system cannot operate. By contrast, a computer system with a non-captive monitor is such that any monitor can be plugged into a monitor jack in the side of the CPU box of the system. Previously, there have been no monitors with power-down features; thus, a captive-monitor system is ideal for the present invention, since the monitor and the CPU must work in special cooperation to power-down the monitor. In the present invention a signal is sent to the monitor 40 from the CPU system 20 commanding the monitor 40 to power down the selected elements. In the preferred embodiment, this signal is encoded in the monitor control signals 30 in Figure 2. The monitor control signals 30 include red-green-blue (RGB) video signals and horizontal and vertical sync signals. The sync signals are turned off, or brought to zero, thus signaling the monitor to turn off the selected elements. Control circuitry 56 (Fig. 3) in the monitor 40 detects whether the

sync signals are off and then turns off the selected elements through control wires 58 in response thereto. Then when the sync signals are turned back on, the control circuitry 56 turns the selected elements back on. In the foregoing preferred embodiment, the RGB video signals are not turned off. However, in another embodiment, these signals are used to command the monitor 40 to turn off the heating filament 42 in addition to the other selected power-consuming elements, effectively turning off the entire monitor 40 except for a small circuit in the control circuitry 56 that monitors the monitor control signals 30 in order to turn the monitor 40 back on. Thus, the monitor 40 can detect when the CPU box 20 has been turned off and can put itself into low power mode until the user turns the CPU box 20 back on. A person skilled in the art will recognize that there are many ways to send the signals for commanding the monitor to turn the selected elements on and off. For example, in one embodiment, the timing of the sync signals may be changed, instead of sending the signals to zero. In another embodiment, separate power mode signal wires 24 (Fig. 1) are used to send the signals. In this embodiment, one wire carries a simple on/off signal. The person skilled in the art will recognize that this is not an all-inclusive list of the ways to send the signals. In the preferred embodiment, the power to the heating filament 42 is slightly reduced. This power reduction adds additional power savings, but does not reduce the temperature of the filament 42 too much, so that the filament 42 can be returned to its normal operating temperature in approximately two seconds. In many monitors the normal operating voltage applied to the filament 42 is 6.3V. In the present invention, the voltage is reduced to approximately 5V. Figure 4 shows the 6.3V source applied to the filament 42 through wire 72. The 5V source is applied through diode 70 and wire 74 to the filament 42. In this arrangement, when the 6.3V source is turned on, the diode 70 is reversed biased, so the filament 42 receives the 6.3V. When the control circuitry 56 receives the signal to put the monitor 40 in the low power mode, the 6.3V source is

turned off, so the diode becomes forward biased and the 5V source is applied to the filament 42. A person skilled in the art will recognize that the 5V source can come from any source. For example, in the embodiment shown in Figure 1, the 5V can come through the power mode signal wires 24 in a separate wire or as part of the on/off signal. In another embodiment, the 5V source may be a standby source within the power supply or control circuitry 56 of the monitor 40.