WO2009133512A1

WO2009133512A1 - Power management

Info

Publication number: WO2009133512A1
Application number: PCT/IB2009/051699
Authority: WO
Inventors: Sylvain Mousset
Original assignee: Nxp B.V.
Priority date: 2008-04-30
Filing date: 2009-04-24
Publication date: 2009-11-05

Abstract

A method of providing electrical power to an integrated circuit (120) operable in an active mode and an inactive mode, the method comprising: providing a first circuit (113) for supplying electrical power from a power source to the integrated circuit in the inactive mode; providing a second circuit (112) for supplying electrical power from the power source to the integrated circuit in the active mode; supplying electrical power to the integrated circuit from the first circuit when the integrated circuit is in the inactive mode; and selecting the second circuit to supply electrical power to the integrated circuit in the inactive mode in place of the first electrical circuit when the efficiency of supplying power from the second circuit exceeds that of the first circuit.

Description

DESCRIPTION

POWER MANAGEMENT

The invention relates to electrical power management for integrated circuits, and in particular to methods and apparatus for optimising efficiency of supply power to integrated circuits.

Power management units for mobile devices such as cellular radio communications devices (or cellphones) often include two power supply regulators for supplying power to a baseband integrated circuit (IC): one for when the device is in an active operating state; the other for when the device is in an inactive state.

Typical power supply regulators are in the form of DC-DC voltage regulators and linear voltage regulators. DC-DC regulators tend to be more efficient at higher operating loads, while linear voltage regulators tend to be more efficient at lower operating loads. It is known to use two such regulators in combination, switching between them depending on the mode of operation. This extends the operation time between battery charges, because energy consumption is reduced overall, when taking into account typical use of a cellphone where the baseband IC is in the inactive state for much of the time the cellphone is switched on.

It is an object of the invention to further increase the efficiency of operation of supplying electrical power to an integrated circuit operable in active and inactive modes.

In accordance with a first aspect, the invention provides a method of providing electrical power to an integrated circuit operable in an active mode and an inactive mode, the method comprising: providing a first circuit for supplying electrical power from a power source to the integrated circuit in the inactive mode; providing a second circuit for supplying electrical power from the power source to the integrated circuit in the active mode; supplying electrical power to the integrated circuit from the first circuit when the integrated circuit is in the inactive mode; and selecting the second circuit to supply electrical power to the integrated circuit in the inactive mode in place of the first electrical circuit when the efficiency of supplying power from the second circuit exceeds that of the first circuit.

In accordance with a second aspect, the invention provides a power management unit for providing electrical power to an integrated circuit operable in an active mode and an inactive mode, the power management unit comprising: a first circuit for supplying electrical power from a power source to the integrated circuit in the inactive mode; a second circuit for supplying electrical power from the power source to the integrated circuit in the active mode; a power supply regulator configured to select the second circuit to supply electrical power to the integrated circuit in the inactive mode in place of the first electrical circuit when the efficiency of supplying power from the second circuit exceeds that of the first circuit.

The invention will now be described by way of example, and with reference to the accompanying drawings in which: figure 1 is a functional schematic diagram of a power management unit connected to a baseband IC; figure 2 illustrates the relationship between leakage current drawn by an IC as a function of temperature; figure 3 illustrates the differing relationships between battery consumption as a function of baseband core current for a linear regulator and a DC-DC regulator; and figure 4 illustrates an optimised relationship between battery consumption as a function of baseband core current.

Shown in figure 1 is a schematic functional diagram of a power management unit IC 110 connected to a baseband IC 120 via a voltage supply line 130 and control bus 140. The core 121 of the baseband IC 120 is supplied a voltage by the power management unit IC 1 10 via the voltage supply line 130, and a control module 122 of the baseband IC 120 communicates with the power management IC 1 10 via the control bus line 140. Other components may also be present in the baseband IC, but the core 121 generally predominates in terms of consumption of electrical power. The power management unit IC comprises a pair of voltage regulators 1 12, 113, each regulator connected to an input 1 11 for receiving electrical power, typically from a battery-powered voltage supply. The outputs of each regulator 112, 1 13 are connected to a switch (or multiplexer) 114, which allows each regulator to be selected for supplying electrical power via the voltage supply line 130 to the baseband IC 120.

In the configuration shown in figure 1 , the first regulator is a linear voltage regulator (LDO) 1 13, and the second is a DC-DC voltage regulator 112. A switch (or multiplexer) controller 1 15 is connected to the switch 1 14 and configured for controlling which regulator is selected. The switch controller 1 15 is connected to the control module 122 on the baseband IC 120 via the control bus line 140.

In normal operation, the control module 122 determines whether the core 121 of the baseband IC 120 is in an active or an inactive mode. The control module 122 sends signals over the control bus 140 to the switch controller 1 15 to select the appropriate regulator to be used to supply the baseband IC with electrical power. Since the linear regulator 113 is more efficient than the DC-DC regulator 112 at lower supplied currents, the control module 122 instructs the switch controller 1 15 to select the DC-DC regulator only when the baseband IC 120 is in an active mode, e.g. when instructions are being executed on the core 121 .

When in the active mode, the DC-DC regulator 112 is able to deliver the high current required by the baseband IC 120. When in the inactive mode, the linear regulator (LDO) 1 13 is used to reduce the quiescent current of the power supply. During the inactive (or sleep) mode, an important contributor to total current consumption is the processor of the core 121 (through its core supply domain). This current consumption is mainly the result of leakage currents. Such leakage currents depend on process variations and on temperature. Process variation becomes more important with new IC technologies, e.g. as the feature size possible on integrated circuits is reduced. Present technologies are being used and developed at the sub-100nm range. A trade off between performance (e.g. given by a maximum frequency of operation) and leakage current is generally achieved for a given IC. However, over a typical operating range for a baseband IC, there may be a substantial range of leakage current between different nominally identical devices. Such variations may be as high as a factor 2 between a typical piece and a worst case. Temperature of operation also has also a large impact on leakage current as illustrated in figure 2, which shows the relationship 210 between leakage current (l_core) as a function of temperature for a core of a typical baseband IC. The leakage current rises from around 240 μA at 25 ⁰C to around 490 μA at 45 ⁰C, i.e. roughly doubling in magnitude over this temperature range.

The result of the above is that baseband IC power consumption during sleep mode in typical use may vary by a factor of four as a result of the combination of process and temperature variations. This needs to be accounted for in the overall design of the baseband and power management unit ICs. Depending on the power consumption of the baseband IC 120 during inactive use, it may therefore be more efficient to provide the voltage supply with a DC-DC regulator 112 rather than with a linear voltage regulator 113. The decision on which is more efficient at any given time will depend on the current drawn (including leakage current) by the baseband IC 120, which in turn depends on the temperature of the IC 120 and any variation in leakage current resulting from process variations, which will cause differences between individual ICs (or between batches of ICs).

Figure 3 illustrates the relationship between battery consumption as a function of baseband core consumption for an exemplary DC-DC regulator (indicated by line 310) and linear regulator (indicated by line 320). At low currents, in the illustrated case below around 500 μA (indicated by the vertical dashed line 330), use of the DC-DC regulator 1 12 results in a higher battery consumption current than use of the linear voltage regulator 113. At higher currents, above around 500 μA, use of the linear voltage regulator 113 results in a higher battery consumption current than use of the DC-DC regulator 1 12. The current relationship can therefore be defined by a low power region 340 and a high power region 350. The border 330 between the low power region 340 and the high power region 350, i.e. the point at which the current relationships 310, 320 cross-over, is dictated by the characteristics (e.g. quiescent current and efficiency) of the particular regulators being used.

Consequently, the switch control 1 15 of figure 1 is configured to select the DC-DC regulator to supply electrical power to the baseband IC in the inactive mode in place of the linear regulator when the efficiency of supplying power from the DC-DC regulator exceeds that of the linear regulator, i.e. in the high power region 350, and is configured to select the linear regulator when in the low power region. The resulting optimised relationship between battery consumption current and baseband core consumption current is shown in figure 4. The optimised relationship (indicated by line 410) saves on battery consumption current in both the low power region 340 (the saving indicated by arrow 420) and the high power region 350 (the saving indicated by arrow 430).

Under these conditions, the impact on the standby time for an exemplary second generation (2G) cellphone is shown in the table below.

The use of an optimised power supply configuration can therefore result in a saving of around 14% in current consumption when the baseband IC is inactive (e.g. when the cellphone is in standby mode), thereby extending the time between required charging operations.

Through knowledge of which region the baseband IC is currently operating in, the power management unit 110 is able to supply power to the baseband IC with optimum efficiency. By defining the borderline 330 between the regions 340, 350, and by knowing the current consumption characteristics of the baseband IC, it becomes possible to determine the most efficient way to supply the core when in the inactive mode.

The borderline value 330 between the low power and high power regions 340, 350 can be determined during a production test, once the current consumption in inactive mode has been determined. The current value can then be stored in non-volatile memory. The value can then be used by the operating software of the cellphone during use, with the control module 122 determining when the current exceeds the borderline value 330. Because the core current will vary with temperature, the power management unit IC 1 10 may be configured to switch between voltage supply regulators if the temperature exceeds a present level, for example on instruction from the control module 122. This level may be preset on manufacture, after determining the current-temperature characteristics. A temperature sensor connected to the control module 122 may be used for this purpose, with the control module 122 selecting the appropriate regulator 112, 113 for a given measured temperature. The temperature sensor may be on-chip or external to the baseband IC 120. The above solution allows for a reduction in power consumption in particular for mobile devices that use baseband ICs having a high standby current consumption. The solution also allows variations in power consumption due to external conditions to be accounted for. The solution does not aim to reduce the baseband ICs own power consumption but to select the most efficient way of supplying it with power.

The above described invention can be used for many kinds of portable devices that require ICs having varying current characteristics, and is particularly suitable for mobile telephony applications.

Other embodiments are intentionally within the scope of the invention as defined by the appended claims.

Claims

1. A method of providing electrical power to an integrated circuit operable in an active mode and an inactive mode, the method comprising: providing a first circuit for supplying electrical power from a power source to the integrated circuit in the inactive mode; providing a second circuit for supplying electrical power from the power source to the integrated circuit in the active mode; supplying electrical power to the integrated circuit from the first circuit when the integrated circuit is in the inactive mode; and selecting the second circuit to supply electrical power to the integrated circuit in the inactive mode in place of the first electrical circuit when the efficiency of supplying power from the second circuit exceeds that of the first circuit.

2. The method of claim 1 wherein the second circuit is selected when a current drawn by the integrated circuit exceeds a preset level.

3. The method of claim 1 wherein the second circuit is selected when a measured temperature exceeds a preset level.

4. The method of any preceding claim wherein the first circuit is a linear voltage regulator.

5. The method of any preceding claim wherein the second circuit is a dc-dc voltage convertor.

6. The method of any preceding claim wherein the integrated circuit is a baseband integrated circuit for a hand portable electronic communication device.

7. A power management unit for providing electrical power to an integrated circuit operable in an active mode and an inactive mode, the power management unit comprising: a first circuit for supplying electrical power from a power source to the integrated circuit in the inactive mode; a second circuit for supplying electrical power from the power source to the integrated circuit in the active mode; a controller configured to select the second circuit to supply electrical power to the integrated circuit in the inactive mode in place of the first electrical circuit when the efficiency of supplying power from the second circuit exceeds that of the first circuit.

8. The power management unit of claim 7 wherein the controller is configured to select the second circuit when a current drawn by the integrated circuit exceeds a preset level

9. The power management unit of claim 7 wherein the controller is configured to select the second circuit when a measured temperature exceeds a preset level.

10. The power management unit of any of claims 7 to 9 wherein the first circuit is a linear voltage regulator.

11. The power management unit of any of claims 7 to 10 whereinr-the second circuit is a dc-dc voltage converter.

12. A communications device comprising the power management unit of any of claims 7 to 11 and a baseband integrated circuit connected to the power management unit for supply of electrical power therefrom.

13. The communications device of claim 12 wherein the controller comprises a control module configured to determine when the efficiency of supplying power from the second circuit exceeds that of the first circuit and a switch controller configured to select the first or second circuit to supply electrical power to the baseband integrated circuit in response to a signal supplied by the control module.