US 20090121729 A1
Load current of a circuit is determined across a component of the circuit by calibrating the resistance of the component with a reference current having a distinguishable characteristic. For example, a reference current with swept frequency modulation is applied to the component so that the resistance of the component is determined from voltage drop associated with the reference current across the component. The component resistance is applied to a voltage drop associated with the load current to determine the load current. For example, a filter matched to the reference current frequency modulation isolates the reference current voltage drop so that a ratio of the reference current voltage drop and the load current voltage drop provides a ratio of the reference current and load current.
1. A method for measuring a load current of a circuit, the circuit having plural components, the method comprising:
adding a reference current to the load current, the reference current having a distinguishable characteristic;
analyzing the reference current with the distinguishable characteristic at a selected of the plural components to determine the resistance across the selected component; and
applying the determined resistance across the selected component to determine the load current.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
8. An information handling system comprising:
plural components operable to process information;
a power supply having plural electronic components, the power supply operable to provide a load current to power the processing components; and
a current detector interfaced with an electronic component, the current detector operable to apply a reference current to the electronic component, the reference current having a distinguishable characteristic, and to analyze the reference current to determine the load current across the electronic component.
9. The information handling system of
10. The information handling system of
11. The information handling system of
12. The information handling system of
determining the resistance across the electronic component; and
applying the determined resistance of the electronic component to determine the load current.
13. The information handling system of
14. The information handling system of
15. A system for detecting load current across an electronic component, the system comprising:
a differential amplifier operable to detect voltage drop across the electronic component;
a reference current generator operable to generate a reference current having a distinguishable characteristic and to apply the reference current to the electronic component;
a component resistance detector operable to analyze the reference current and voltage drop to determine a resistance of the electronic component; and
a load current detector operable to apply the determined resistance and voltage drop to determine the load current across the electronic component.
16. The system of
17. The system of
18. The system of
19. The system of
20. The system of
1. Field of the Invention
The present invention relates in general to the field of information handling system circuits, and more particularly to a system and method for current measurement.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems perform most processing functions with integrated circuits (ICs), however, a number of other electrical circuits are typically included so that the ICs can communicate with each other and have power. Generally, IC communication and power circuits run through printed circuit boards (PCBs), such as a motherboard and daughter boards. The motherboard typically supports a central processing unit (CPU), chipset and memory, such as RAM, while daughter boards typically interface with the motherboard to support specific functions, like graphics. ICs typically operate with power supplied through power pins at a defined constant voltage. In some instances, the power drawn by an IC varies dramatically during normal operations, such as when a CPU transitions from an idle state having minimal computations to an active state performing complex operations. As the number of transistors on CPUs continues to increase, variations in power demanded by CPUs during normal operating conditions also tends to increase. Precise power management also presents a challenge in other information handling system applications, such as with hot-swap controllers.
Precise power management generally calls for precise current measurement at various locations throughout an information handling system. One common method of current measurement is a Hall sensor that measures the magnetic field around the current conductor. However, Hall sensors are relatively expensive. A less expensive method for current measurement is to flow the current through a precision shunt resistor and measure the voltage drop across the shunt resistor. In order to accurately measure current, the shunt resistor is built to provide a constant resistance across a variety of operating conditions, such as variations in temperature. A difficulty with shunt resistors is that the voltage drop across the shunt resistor wastes power and produces heat as a byproduct of the current measurement. Other less precise resistors are sometimes used to detect overcurrent situations. For example, a MOSFET Rdson detects an overcurrent by assuming a nominal resistance value and measuring the voltage drop across the resistance. Precise current measurements are not attempted since a precise resistance value is not known, however, for determining gross overcurrent conditions, such as might result from a short to ground, the nominal resistance value provides an accurate enough estimation.
Therefore a need has arisen for a system and method which measures current by a voltage drop across a resistor having variable resistance values.
In accordance with the present invention, a system and method are provided which substantially reduce the disadvantages and problems associated with previous methods and systems for measuring current. A reference current having a distinguishable characteristic is added to a load current at a component of an electrical circuit. Voltage drop associated with the reference current is isolated to calibrate the resistance of the electrical component. The resistance determined for the electrical component is applied to the voltage drop of the load current across the electrical component to determine the load current.
More specifically, an information handling system has plural processing components to process information. A power supply provides power to the processing components with a variety of electronic components, such as a MOSFET, copper wire lines and connectors. A current detector interfaces with a selected component, such as a MOSFET, and applies a reference current having a distinguishable characteristic at the selected component in addition to the load current in order to calibrate the resistance of the selected component. The calibrated resistance of the component is determined and applied in order to determine the load current across the component. For instance, a differential amplifier measures the total drop in voltage across the component. A component resistance detector has a first filter that isolates the drop in voltage associated with the reference current and a second filter that isolates the drop in voltage associated with the load current. A load current detector generates a ratio of the first and second voltage drops to cancel the resistance and leave the ratio of the reference current and load current. One example of a distinguishable characteristic is frequency modulation, such as swept frequency modulation that is isolated with a matched filter having a peak voltage hold.
The present invention provides a number of important technical advantages. One example of an important technical advantage is that current measurement becomes possible across virtually any resistance by monitoring the value of the resistance as current measurements are taken. This reduces the expense of current measurement by reducing or eliminating the need to add resistors to a circuit solely for the purpose of current measurement. Instead, existing resistance is used to measure current by monitoring the resistance value as current is measured. Avoiding the use of precision shunt resistors improves the efficiency with which information handling systems use power and reduce heat produced by information handling system operation. Further, avoiding the use of precision shunt resistors helps prevent the design of power systems having a single point of failure at the shunt resistor.
The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element.
Load current across an information handling system circuit is determined by measuring resistance of a component in the circuit and voltage drop across the component. For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components.
Referring now to
Referring now to
By isolating the voltage Vref of the reference current from the total voltage Vds Rdson is calculated with the known value of Iref.
To allow for the isolation of Vref, Iref is provided with a distinguishable characteristic, such as spreading the Iload in the frequency domain to widen and lower its power spectrum relative to Iref so that Iload is more easily filtered out and rejected. Since the Iload is not controlled or adjustable, a timing and chirp generator 36 instead spreads the reference current using frequency modulation of the time base at generation of the reference current. The frequency modulation timing is provided to load current detector 32, depicted in the example embodiment as an analog-to-digital converter and to a matched bandpass filter 38 having peak voltage hold. Component resistance detector 30 compares the filtered signal from matched bandpass filter 38 with the signal from a lowpass filter 40 to analyze the resistance of MOSFET 12. For example, the clock frequency over bandpass filter center frequency ratio of filter 38 is constant and equal to the division rate of the counter of the ADC load current detector 32. As timing and chirp generator 36 provides a swept “chirp” clock signal having increasing or decreasing frequency for Iref, filter 38 and ADC clock of load current detector 32 also increase or decrease. The peak to peak voltage of filter 38 is captured so the Vds output from filter 38 equals Iref times Rdson times the Gain provided by differential amplifier 28. Lowpass filter 40 outputs a lowpass of Vds which equals Iload times Rdson times Gain of differential amplifier 28. The output from ADC 32 Vin/Vref, which is:
Since Rdson and gain cancel out, the output of ADC 32 is proportional to Iload. In one embodiment, the output of ADC 32 is captured at plural frequencies within the “chirp” bandwidth and averaged to improve the accuracy of Iload measurements.
Referring now to
Referring now to
In alternative embodiments, Iload detection on multiple channels is provided by multiplexing the output from each channel in front of a sense amp, such as for monitoring multiple rails. In addition, monitoring of switching regulators is provided by using the switching frequency of the regulators as another level of modulation so that the MOSFET on time represents a periodic enabling of load current monitoring.
Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.