Design and Implementation of Low-Power Tablet PCs

A tablet PC is a computer larger than a PDA and yet smaller than a notebook PC, which can´t be equipped with a large battery due to the portability requirement of low weight. The machine state controls the power management of a typical tablet PC control of the hard disk, and various powers on/off sequences for more than twenty sets of power supplies. In this paper, we propose a design using a low-power embedded controller which can separately provide the different power sources necessary for different modules in order to reduce the total power consumption. Moreover, the embedded controller can receive the interrupt signal from users and restore the system state from S₅ (Suspend to disk) to S₀ (Run-time state) and from S₃ (Suspend to RAM) to S₀. In our design, the current consumption of 3.08 mA in the S₅ state not only may last more than 50 days but also is 370 times less than the 1150 mA at S₀ state. Moreover, it only consumes 47 mA at S₃. Later, we can even use a lower power version of the embedded controller, and then the design can prolong more of the idle time and sleeping time. Since the embedded controller is programmable, our design can easily fine tune the timing adjustment of the power on/off sequences and for compatibly matching the different version of motherboards. The fine tuning adjustment of the power on/off is based on the nest counters which generate several milliseconds of the time delays. For the different Tablet PC motherboard versions, we need only to modify the control program which is easily programmable and compatible with different chip sets and can easily port on different Tablet PCs