BRIEF DESCRIPTION OF THE DRAWINGS
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.
FIG. 1 depicts a block diagram of a test adapter configured to measure emissions associated with a USB cable interfacing an information handling system and a hard disk drive peripheral;
FIG. 2 depicts a block diagram of a test adapter configured to inject noise at a cable interfacing an information handling system and keyboard peripheral to measure the effectiveness of shielding of the keyboard and cable;
FIG. 3 depicts a circuit diagram of a dual-input resistive divider probe for interfacing with an information handling system external cable; and
FIG. 4 depicts a circuit diagram of a test adapter for measuring the electromagnetic compatibility of an information handling system and peripheral.
DETAILED DESCRIPTION
A test adapter tests for electromagnetic compatibility of an information handling system and peripheral by interfacing with the cable connecting the information handling system and peripheral to detect electromagnetic interference associated with the cable or to inject noise into the cable to test shielding of the peripheral. 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 FIG. 1, a block diagram depicts a test adapter 10 configured to measure emissions associated with a USB cable 12 interfacing an information handling system 14 and a hard disk drive peripheral 16. Information handling system 14 communicates information with hard disk drive 16 through USB cable 12 using standardized USB differential signaling. In alternative embodiments, alternative peripherals can interface with information handling system 14 with alternative cables 12. For example, displays, optical disc drives, mice, keyboards, storage networks or other types of peripherals are interfaced with test adapter 10 using Firewire, SATA, SAS, PCI Express, LVDS, TMDS or other types of serial differential link cables as well as unidirectional link cables, such as a video cable that sends RGB information. Test adapter 10 interfaces with the signals 22 communicated across cable 12, including ground and power signals, and provides a test connector 18 for each signal 22 so that a test instrument, such as a spectrum analyzer 20, can read and analyze the signals 22. As depicted by FIG. 2, analysis of signals 22 from a peripheral 16 to information handling system 14 helps to determine the source of EMI associated with combined operations of peripheral 16 and information handling system 14, such as a common mode component.
Referring now to FIG. 2, a block diagram depicts a test adapter 10 configured to inject noise at a cable 12 interfacing an information handling system 14 and keyboard peripheral 24 to measure the effectiveness of shielding of the keyboard and cable. A noise generator 26 generates emissions of a desired character and injects the noise through a test connector 18 and adapter 10 into cable 12. Test adapter 10, which is shielded to reduce inadvertent emissions, sends noise signals 22 through cable 12 to peripheral 24. A test instrument, such as spectrum analyzer 20, measures emissions from peripheral 24 to analyze the effectiveness of shielding for peripheral 24.
Referring now to FIG. 3, a circuit diagram depicts a dual-input resistive divider probe 28 for interfacing with an information handling system external cable. Resistor divider probe 28 has a first input V130 and second input V232 that each interface with a wire of a differential wire pair. Isolation resistors 34 are high-value resistors in parallel that interface with a test connector 18, such as a coaxial cable. For example, the resistance Rs of isolation resistors 34 is 400 ohms to support connection to a 50 ohm coaxial cable and a 50 ohm test instrument 20 with division ration of approximately 1/10. A small capacitance 36 is added in parallel with isolation resistors 34 to compensate for input capacitance of test instrument 20. As set forth in the equation:
When Rs of isolation resistors 34 times the capacitance Cs of capacitors 36 is substantially equal to the resistance ROUT and capacitance COUT associated with test instrument 20, frequency dependence for test signals falls out. Removal of the frequency dependence by insertion of capacitors 36 in parallel with isolation resistors 34 allow the bandwidth subject to testing to extend to multiple GHz, such as the frequency ranges associated with high speed serial links. In addition to flat frequency measurements, resistor divider probe 28 can be given correction factors for frequency domain measurements. In one embodiment, capacitance 36 is added by wrapping copper tape or other conductive materials over each isolation resistor 34.
Referring now to FIG. 4, a circuit diagram depicts a test adapter 10 for measuring the electromagnetic compatibility of an information handling system and peripheral. In the example embodiment of FIG. 4, cable 12 can be a differential serial link having a differential pair of wires 38 or a unidirectional link having a single ended wire 40. One or more power or ground wires 42 provide cable 12 with power and a ground reference. Test adapter 10 has a shielded housing and cable shields 44 that prevent entry or escape of EMI from test adapter 10. For example, test adapter 10 has opposing USB ports 44 so that a USB cable from an information handling system connects to one port and a cable from a peripheral connects to another port. Within test adapter 10's shielded enclosure, a resistor divider probe 28 interfaces an RF connector 18 with differential pair wires 38 while single probes 46 interface single ended wire 40 and power/ground wires 42 with connectors 18. In order to read signals received from a peripheral, a test instrument is connected to the appropriate connector 18, and in order to provide noise to a peripheral, a noise generator is instead connected to the connector 18. A common mode choke 48 disposed along differential pair wires 38 support testing of EMI with isolation of the common mode component of the signal sent along cable 12.
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.
Patent Application
20080084218
