Patent Application
20090021264
The present invention relates generally to high speed DIMMs and, more specifically, to an apparatus for repeatable drive strength assessments of high speed memory devices, such as DIMMs.
To assess the driver strength of DIMMs in high performance high speed server systems, in prior art systems, there is a need to probe at the chip pad interface while the device is in operation. A DIMM, or a Dual In-line Memory Module, is one popular type of memory module. The DIMM is a rectangular low-profile circuit board that has electrical contact points arranged on both sides along one long edge. The contact points form electrical connections to the main board's memory bus when the DIMM is inserted into a DIMM memory socket. Today, there is the ability to measure at the pin of the chip or memory controller to assess the drive strength. (A memory controller is a chip on a computer's motherboard or CPU die which manages the flow of data going to and from the memory.) The disadvantage is in using this kind of approach is that the trace itself produces unwanted stub loading into the probe and signal under test. (Stub loading on the main bus can be caused by excessively long stubs and/or stubs terminated in low impedances and can load down the main bus and result in transmission line reflections, and therefore waveform distortions. This can have the effect of increasing the bit error rate for terminals receiving data on the bus, or in extreme circumstances, cause terminals to stop receiving completely. More information on stub loading can be found here: http://www.ddc-web.com/FAQ/Databus/Standards.aspx.) Another disadvantage is the uncertainty in being able to repeat the measurement consistently.
Multiple time probing can result in damaging the BGA pins. (A ball grid array (BGA) is a type of surface-mount packaging used for integrated circuits.) Use of sophisticated probe stations is one way to over come this limitation, but probe stations that provide this kind of measurement capability are expensive and cost 100s of thousands of dollars.
There is currently a need for inexpensive test jig for assessing DIMM strength. (A jig is an adapter for connecting electronic devices to a service and maintenance system for testing, debugging and firmware update purposes.)
The present invention is an apparatus for repeatable drive strength assessments of high speed memory DIMMs.
The present invention assesses memory (DIMM) strength by calculating frequency content of a radiated field which is collected by an apparatus, such as a dipole antenna. Radiated field is created by accelerated charge, which is a function of the slew rate or DIMM strength. Radiated power is directly proportional to the frequency at which bits are driven. By separating the radiated field from the near field or stored field, the DIMM strength content is isolated from other functional DIMM issues, such as tRCD latency, refresh cycles, addressing mode, etc. (tRCD latency (RAS to CAS Delay) is the number of clock cycles needed between a row address strobe (RAS) and a column address strobe (CAS). It is the time required between the computer defining the row and column of the given memory block and the actual read or write to that location. tRDC stands for Row address to Column address Delay.) By examining the radiated power, the disadvantages of the prior art, such as by probing the DIMM's contacts, are avoided.
The illustrative aspects of the present invention are designed to solve one or more of the problems herein described and/or one or more other problems not discussed.
These and other features of the invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:
The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represent like elements between the drawings.
The present invention provides an apparatus for repeatable drive strength assessments of high speed memory units, such as DIMMs.
The apparatus of the preferred embodiment has two printed circuit boards, Printed Circuit Board 102 and Printed Circuit Board 104. One board (Printed Circuit Board 102) is configured to radiate utilizing Riser with Dipole Antenna 117 from operational amplifier (Op-Amp 106) for amplifying the data received from Printed Circuit Board 102. An Op-Amp is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. In its ordinary usage, the output of the op-amp is controlled by negative feedback which, because of the amplifier's high gain, almost completely determines the output voltage for any given input. (See http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm.) A dipole antenna is an antenna with a center-fed driven element for transmitting or receiving radio frequency energy. These antennas are the simplest practical antennas from a theoretical point of view. (See http://www.ece.rutgers.edu/˜orfanidi/ewa/.) The Dipole Antenna 117 receives data from the other (Printed Circuit Board 104) which transmits data from Radiating Board 108 based on the concept of reciprocity and the Op-Amp 106 amplifies the data that has been transmitted by Radiating Board 108 and the data is decoded by Decoder 110. The data is then passed to Analyzer 114 which analyzes the data received by the Di-Pole Antenna 117 to determine the strength of the tested DIMMs (such as DIMM 122). On the Radiating Board 108, is a memory controller. The memory controller exercises the DIMM during testing. During testing, the memory controller exercises the DIMM (such as DIMM 122) in read mode, so only the DIMM is driving, and in burst mode, so that an alternating current is created. The test results are radiated by Radiating Board 108 and received by Di-Pole Antenna 117, amplified by Op-Amp 106 and decoded by Decoder 110. Only the memory data lines are radiated in that the control signals (lines 115) are routed around Radiating Board 108 on Control Signal Bus 116. The memory data traces (Data Bus 113) can be routed across open slots in the shield layer that are half a wavelength (lambda λ) long. Each memory controller output buffer is over damped with a series resistor which can be seen in
The present invention allows the system to generate a continuous flow of data out of the memory device and onto the memory data traces (Data Bus 113). In the apparatus of the present invention, the memory controller stores, in the memory DIMM, the data pattern with the highest repetitive pattern and sets up the read operation. The test begins with the memory controller requesting memory data with read commands. The read commands are transferred from the memory controller to the memory device. The read commands configure the memory device to output memory data patterns that are stored in memory.
After the read command operation, the memory control stops transmitting and converts to receive mode. The memory DIMM (122) takes over the data bus, responds with its output driver switching at maximum frequency and exports the requested data pattern as a continuous stream of bits in burst mode. Memory DIMMs output buffer produces alternating cyclic patterns on the data trace (Dipole Antenna 117). Thus, spectral frequency associated with radiation the pattern detected is predominately produced by the memory DIMM's output buffer.
As noted above, the board is configured so the DIMM's data outs are fast switching buffers. A like card 102 has an electric antenna whose half wavelength (lambda λ) matches the DIMM burst mode frequency. The card is positioned like a riser card next to and into the radiating card. The signal radiated is received and amplified with the Op-Amp 106. The received signal is translated into a frequency spectrum display. From the frequency spectrum display, the fundamental frequency magnitude is compared to a reference magnitude. By inspecting the fundamental frequency magnitude against the reference magnitude, the drive strength of the high speed memory device, such as DIMM 122, may be assessed.
The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to an individual in the art are included within the scope of the invention as defined by the accompanying claims.
