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https://designers-guide.org/forum/YaBB.pl Design >> Mixed-Signal Design >> return loss measurement https://designers-guide.org/forum/YaBB.pl?num=1177562648 Message started by smarty on Apr 25th, 2007, 9:44pm |
Title: return loss measurement Post by smarty on Apr 25th, 2007, 9:44pm Hi, I have just started working on high speed SerDes design and I am starting on the receiver supporting PCI-express 2.0 standards(5Gbps). I am starting to understand the different spec and trying out simulations on them to improve my understanding. There is a spec on receiver that it should meed a specified CMRL(common-mode return loss) and DRL(differential return loss). I am simulating this in spectre to measure both. From my understanding, relating to return loss it is measured using the S11 parameter ( please correct me if I am wrong). Can anybody suggest me as to how this can be done? I provide a method I am trying out. Please provide your feedback on this. 1. I have my receiver end terminated to 50ohms. 2. I use the n-port from analog Lib and including the corresponding s-param file to model the package model. 3. I uses a PORT0 from analog Lib to provide my ideal input side voltage source with series resitance as 50ohms( source side resistance). 4. To measure differential RL I use to connect one line to one end of PORT and the other line to the another end of the PORT. I then do an sp analysis and measure the RL as db(s11). Kindly provide your valuble feedbacks, whether this is a correct setup/method to measure return loss. Thanks and Regards, SBR |
Title: Re: return loss measurement Post by Ken Kundert on Apr 25th, 2007, 11:27pm Take a look at the papers on differential measurements in the Analysis section of this site. -Ken |
Title: Re: return loss measurement Post by smarty on Apr 26th, 2007, 1:21am Hi Ken, Thanks for the information. I will look at the papers. Regards, SBR |
Title: Re: return loss measurement Post by smarty on May 14th, 2007, 11:07pm Hi Ken, Could you pls clear me few things regarding the diferential circit testbanch pdf, it would be of much help. 1. I need to measure the common-mode return loss and Differential return loss for PCI-e reciever from dc till 1.25Gz. In normal operation the input varies from +/-600mv from ground on both D+ and D-. I would like to know to have a better understanding, using this setup how can that be measured. I am dotting my understanding. correct me if you find my way different. I would like to use the setup in fig4. To measure, the input to be given are vdm=1.2;vcm=0;Rid=100ohms;Rcm=very high(10K). One more is could we use the PORT cell from analogLib, and define input as a sine wave(freq:2.5GHz, amp:600mv, dc=0) and connect the port to a se2diff cell and use the output of that cell to the reciever input. I am new in this field, and from what I have seen Return loss is measured by s11 parameter(20dB ofs11), by running a sp analysis in spectre. If this is the case, how would I measure return loss for both these setup?. In your experience which would provide, a more realistic method. Kindly help this out for me to have better understanding. Thanks and Regards, SBR |
Title: Re: return loss measurement Post by Ken Kundert on May 15th, 2007, 9:29am It seems like you are on the right track, though it is not clear why you would want to measure the common-mode return loss when the common-mode impedance is not controlled. Also, I don't know what se2diff is, so I cannot say whether its use is appropriate. -Ken |
Title: Re: return loss measurement Post by smarty on May 17th, 2007, 5:33am Ken, Thanks for your inputs. Common-mode return loss is measured as a part of the PCIe specs. Best Regards, SBR |
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