1、 EIA STANDARD TP-108 Impedance, Reflection Coefficient, Return Loss, and VSWR Measured in the Time and Frequency Domain Test Procedure for Electrical Connectors, Cable Assemblies or Interconnection Systems EIA-364-108 July 2000 EIA-364-108 ANSI/EIA-364-108-2000(R2013) Approved: July 7, 2000 Reaffirm
2、ed: January 15, 2013 NOTICE EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtai
3、ning with minimum delay the proper product for his particular need. Existence of such Standards and Publications shall not in any respect preclude any member or nonmember of ECIA from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such
4、 Standards and Publications preclude their voluntary use by those other than ECIA members, whether the standard is to be used either domestically or internationally. Standards and Publications are adopted by ECIA in accordance with the American National Standards Institute (ANSI) patent policy. By s
5、uch action, ECIA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard or Publication. This EIA Standard is considered to have International Standardization implication, but the International Electrotechnical Commission activit
6、y has not progressed to the point where a valid comparison between the EIA Standard and the IEC document can be made. This Standard does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard
7、 to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (Created under Standards Proposal No. 4454-A formulated under the cognizance of the CE-2.0 Committee on EIA National Connector and Socket Standards and reaffirmed under
8、Standards Proposal No. 5253.08). Published by Electronic Components Industry Association 2013 Engineering Department 2214 Rock Hill Road, Suite 170 Herndon, VA 20170 PLEASE! DONT VIOLATE THE LAW! This document is copyrighted by the ECIA and may not be reproduced without permission. Organizations may
9、 obtain permission to reproduce a limited number of copies through entering into a license agreement. For information, contact: IHS 15 Inverness Way East Englewood, CO 80112-5704 or call USA and Canada (1-877-413-5184), International (303-397-7956) i CONTENTS Clause Page 1 Introduction 1 1.1 Scope 1
10、 1.2 Object . 1 1.3 Definitions 1 2 Test resources . 3 2.1 Equipment 3 2.2 Fixture 4 3 Test specimen . 6 3.1 Description . 6 4 Test procedure 6 4.1 Time domain 6 4.2 Frequency domain 8 5 Details to be specified 10 6 Test documentation 11 Figure A.1 Example of rise time measurement points . A-1 A.2 E
11、xample of TDR output; 2 curves (different rise times) and start and stop specimen points A-2 A.3 Example of analyzer output, impedance vs. log frequency plot . A-3 C.1 Typical mother board test fixture . C-2 C.2 Typical daughter board test fixture . C-2 C.3 Example of near end reference trace C-5 D.
12、1 Example of an impedance profile of connector using a measurement system rise time of 35 ps D-1 D.2 Example of impedance profiles of cable under the rise time of 35 ps and 1 ns . D-2 E.1 Single-ended terminations E-1 E.2 Differential (balanced) terminations E-2 G.1 Microstrip (a) and stripline (b)
13、geometries . G-1 G.2 Buried microstrip geometry G-2 ii Annex Page A Measurement system rise time (normative) . A-1 B Determination of the near end and far end of the specimen (informative) B-1 C Calibration standards and test board reference traces (informative) C-1 D Interpreting TDR impedance grap
14、hs (informative) D-1 E Terminations - electrical (informative) E-1 F Practical guidance variable rise time (informative) . F-1 G Printed circuit board design considerations for electronics measurements (informative) . G-1 H Test signal launch hardware (informative) . H-1 EIA-364-108Page 1TEST PROCED
15、URE No. 108 IMPEDANCE, REFLECTION COEFFICIENT, RETURN LOSS, AND VSWR MEASURED IN THE TIME AND FREQUENCY DOMAIN TEST PROCEDURE FOR ELECTRICAL CONNECTORS, CABLE ASSEMBLIES OR INTERCONNECTION SYSTEMS (From EIA Standards Proposal No. 4454-A, formulated under the cognizance EIA CE-2.0 Committee on Nation
16、al Connector Standards.) 1 Introduction 1.1 Scope This procedure applies to interconnect assemblies, such as electrical connectors, and cable assemblies. 1.2 Object This standard describes test methods to measure impedance, reflection coefficient, return loss, and voltage standing wave ratio (VSWR)
17、in the time and frequency domains. NOTE These test methods are written for test professionals who are knowledgeable in the electronics field and are trained to use the referenced equipment. Because the measurement values are heavily influenced by the fixturing and equipment this method cannot descri
18、be all of the possible combinations. The major equipment manufacturers provide Application Notes for more in-depth technical description of how to optimize the use of their equipment. It is imperative that the referencing document include the necessary description and sketches for the test professio
19、nal to understand how to setup and perform the requested measurements. 1.3 Definitions 1.3.1 Measurement system rise time Rise time measured with the fixture in place, without the specimen, and with filtering (or normalization). Rise time is typically measured from 10% to 90% levels. 1.3.2 Specimen
20、environment impedance The impedance presented to the signal conductors by the fixture. This impedance is a result of transmission lines, termination resistors, attached receivers or signal sources, and fixture parasitics. EIA-364-108 Page 2 1.3.3 Reflection coefficient The ratio of the reflected to
21、incident voltages at any given point. The reflection coefficient is given by: Gamma ()= VreflectedVincident= Z L Z OZ L Z O= s11where ZL is the fixture or specimen impedance and ZO is the specimen environment impedance. NOTE In the time domain, the reflection coefficient symbol typically used is rho
22、 (), while Gamma () is used for frequency domain measurements. 1.3.4 Impedance The total opposition that a circuit offers to the flow of alternating current or any other varying current at a particular frequency. It is a combination of the resistance (R) and reactance (X) measured in ohms ( ). The e
23、quation for impedance as a function of s-parameters is: nullnullnullnullnullnullnullnullnullnullnullnullnullnull= R + jX = Z0 nullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnull 1.3.5 Return loss The ratio in decibels (dB) of the power incident upon the impedance discontinuity to the po
24、wer reflected from the discontinuity. The equation for return loss calculated from the reflection coefficient is: Return Loss = 20 log10 | = 20 log10 |s11| 1.3.6 Voltage Standing Wave Ratio (VSWR) The ratio of the maximum magnitude of the voltage on a line to the minimum magnitude at any given point
25、. VSWR can be expressed by the following equations: VSWR Vmax Vmin Vinc VreflVinc Vreflor EIA-364-108Page 31.3.7 Scattering parameter (s-parameter), s11The reflection coefficient at the input port of the device under test, defined as the ratio of the reflected voltage to the incident voltage. 1.3.8
26、Termination (electronics usage) An impedance connected to the end of a transmission line, typically to minimize reflected energy on the line. 1.3.9 Step amplitude The voltage difference between the 0% and 100% levels, ignoring overshoot and undershoot. 2 Test resources Care should be taken when esta
27、blishing the equivalence between time and frequency domain measurements. The relationship between the two is complex and the application of bandwidth = (0.35/rise time) should not be used without further computations and understanding. 2.1 Equipment 2.1.1 Time domain 2.1.1.1 A Time Domain Reflectome
28、ter (TDR) is preferred, although an oscilloscope and pulse generator may be used. A network analyzer may be used with FFT (Fast Fourier-Transform) software. NOTE The test professional should be aware of limitations of any math operation performed by an instrument (e.g., FFT). 2.1.1.2 Variable rise t
29、ime A means should be provided for varying the signal rise time if required. This may be included within the test equipment itself, or possibly through additional filtering or software. NOTE The test professional should be aware of limitations of any math operation performed by an instrument or soft
30、ware; e.g., normalization or filtering. EIA-364-108 Page 4 2.1.1.3 Differential measurements The test equipment shall have the capability to perform differential measurements directly, or provisions shall be made to calculate the impedance from multiple single-ended measurements. 2.1.2 Frequency dom
31、ain 2.1.2.1 A vector network analyzer or impedance analyzer shall be used. NOTES 1 The test professional should be aware of the frequency limitations of the fixture. 2 The test professional should be aware of any limitations of any mathematical functions performed (e.g., normalization, inverse FFT,
32、or software filtering.) 2.1.2.2 Differential measurements For differential measurements, a network analyzer and baluns may be used. NOTE The test professional should be aware of the electrical characteristics of the baluns, that become part of the test fixture and can significantly affect the measur
33、ement. 2.2 Fixture The fixture(s) shall allow for enough measurements throughout the specimen such that variations in geometries, materials, transmission paths, etc. may be demonstrated and provide a representative sampling of specimen performance. NOTE The fixture geometry and materials will impact
34、 the measurements due to the fixture parasitics. Usually the products intended use dictates the most meaningful way to fixture it. 2.2.1 Specimen environment impedance Unless otherwise specified in the referencing document, the specimen environment impedance shall match the impedance of the test equ
35、ipment. Typically this will be 50 ohms for single ended measurements and 100 ohms for differential measurements. 2.2.2 Terminations When using termination resistors, care should be taken to minimize the parasitic reactances of the terminators over the range of test frequencies; see annex E. EIA-364-
36、108Page 52.2.3 Calibration features See annex C for calibration and reference traces. NOTE The term “calibration” used in this document is not to be confused with the periodic factory equipment calibration. Calibration is used in the sense of characterizing the fixture so that when the “fixture plus
37、 specimen” measurement is taken, the characteristics of the specimen alone can be accurately determined. 2.2.3.1 Time domain The fixture shall include features such that the near and far ends of the specimen may be determined in time; see annex B. The calibration plane should be as close to the spec
38、imen as possible. When the fixture includes a pc board with line traces connecting two connectors, it shall have a reference trace(s) that will allow the measurement system rise time to be measured. The reference trace shall have starting points and endpoints at the same location as the DUT starting
39、 point and end point. This is because the reference trace(s) length shall be the same as the pc board traces. 2.2.3.2 Frequency domain It is necessary to include fixture features that will allow for the open, short, and load measurements to be taken. This may be accomplished by one of two methods. F
40、irstly, provide reference traces that include the open, load and short standards. Secondly, provide an interface where these standards can be applied directly to the end of the fixture and immediately before the input plane of the device under test. When using the open/short method, the fixture shal
41、l include features such that measurements may be conducted with the far end of the driven line both open- circuited and short-circuited. NOTE Other calibration techniques (such as Through-Reflect-Line) may be used. The fixture shall incorporate features appropriate to that calibration method(s). 2.2
42、.4 Single-ended The fixture shall allow one signal line to be driven at a time. The far end of the driven line shall be terminated in the specimen environment impedance (typically 50 ohms). It is recommended that a length of transmission line be added after the sample that has a propagation delay gr
43、eater than twice the measurement system rise time. Unless otherwise specified in the referencing document: EIA-364-108 Page 6 a 1:1 signal to ground ratio shall be used, designated ground lines shall be commoned on both the near and far end, adjacent signal lines shall be terminated in the specimen
44、environment impedance. 2.2.5 Differential The fixture shall allow one signal pair to be driven at a time. The driven pair shall be terminated in the specimen environment impedance (typically 100 ohms). It is recommended that a length of transmission line be added after the specimen that has a propag
45、ation delay greater than twice the measurement system rise time. Unless otherwise specified in the referencing document: a 2:1 signal to ground ratio shall be used (one signal pair for each ground return), designated ground lines shall be commoned on both the near and far end, adjacent signal lines
46、shall be terminated in the specimen environment impedance. NOTE For differential applications in the frequency domain using a 2-port network analyzer, the fixture will include the use of baluns. 3 Test specimen 3.1 Description For this test procedure the test specimen shall be as follows: 3.1.1 Sepa
47、rable connectors A mated connector pair. 3.1.2 Cable assembly Assembled connectors and cables, and mating connectors. 4 Test procedure 4.1 Time domain 4.1.1 Calibrate the equipment and fixture according to the manufacturers specified measurement techniques using precision impedance standards and/or
48、cabling. The calibration plane is to be directly at the input interface of the specimen; see 2.2.3.1 for more detailed information. EIA-364-108Page 7 4.1.2 Connect the TDR signal line(s) to the reference line(s) of the test fixture. 4.1.3 Unless otherwise specified in the referencing document, the s
49、ignal rise time shall be the fastest signal of which the equipment is capable. If a slower signal rise time is also desired to approximate the application conditions, one of the rise times in table 1 may be used. Measure and record the measurement system rise time from the reference line, as shown in figure A.1. Table 1 - Additional measurement system rise time (including fixture and filtering) Typical application rise time in which the specimen will be used, Picoseconds Measurement system rise time, picoseconds 100 -
