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Signal Equalization Apparatus for Multi Node System

IP.com Disclosure Number: IPCOM000167870D
Original Publication Date: 2008-Feb-22
Included in the Prior Art Database: 2008-Feb-22
Document File: 5 page(s) / 274K

Publishing Venue

IBM

Abstract

The USB 1.1 structure in BladeCenter* defined as a multiple drop network, where it has thirteen, 10 inch stub associated in given connection. Since USB 1.1 is 12Mb/s data rate, one would think that the multiple drop topology should not be a problem. The topology generates multiple reflection of transmitted signal that would create unpredictable waveform distortion which would interfere the proper function of Management Module. This kind of implementation created system on halt mode for key board and mouse operation for BladeCenter chassis in field. The special equalization circuit on management module reduce the reflection and enhance desire signal there by improve signal quality and restore the function to BladeCenter chassis.

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Signal Equalization Apparatus for Multi Node System

Created the equivalent electrical model of actual network and generated/analyze frequency response. The interpretation of transfer function indicated that significant distortion in pass band and the unnecessary higher gain at higher frequency. Simulation was done to create return loss (S11) estimate of entire multidrop network. In pass band the return loss was not adequate which indicated the poor matching condition on the network and mostly due to multidrop network. Compensation network was generated from return loss data. The compensation network is accomplished using an LCR circuit as shown in Figure 6. The compensation/Equalization circuit on management module reduce the reflection and enhance desire signal there by improve signal quality. This three passive component solved major crisis of BladeCenter chassis. . This invention provided extremely low cost solution compare to replacing 80000 blade or 20000 chassis in field and system down time for customers. The compensation network was easy to rework on Management Module to provide quick solution to customers. Since Management module is hot swap able so there is no down time for customers.

Figure 1 illustrates the USB 1.1 topology implemented in BladeCenter environment. USB Host Controller on each blade connects to backplane via line length of 10 inch On each blade there is a hi-z switch which connects or disconnects USB bus to midplane. The following is the summary of system load configuration for given path.

Total Capacitance = Capacitance on 13 bus switch + Capacitance of bus switch + 14 blade trace capacitance 415PF = 110PF + 25 PF + 280 PF

A - BUS

3

3

Figure 1.

Figure 2 shows waveforms measured at management module with out any compensation network. These waveforms show the failing condition, which will be eliminated.

1 2 4 14

MM1

MM2

1 2 4 14

Unbalance topology

B - BUS

1

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Figure 2.

Figure 3 illustrates the frequency response of unbalance topology which shows the loss increase with frequency increase. That is, this is the frequency response of the failing condition. It is not a flat response at frequency of interest. This does not indicate the typical transmission line frequency response. It is not a f...