EN 60512-23-4-2001 pdf download.Connectors for electronic equipment —Tests and measurements Part 23-4: Screening and filtering tests —Test 23d: Transmission line reflections in the time domain.
A.1 Typical connector reflection test set-up
For board-to-board connectors this transmission line Is provided by two printed circuit test boards incorporating a controlled characteristic impedance trace construction. (refer to figure Al). The mated connector-under-test is mounted between test board 1 and test board 2 in a fashion similar to its intended application. The TDR instrument is connected to test board 1 by means of a coaxial test cable, whose characteristic impedance matches the nominal impedance of the TDR (typically 50 c or 75 (]). The far end of the test signal line on test board 2 is terminated with a resistive termination (see clause A.3 below). These boards shall provide for appropriate microwave quality cable or probe connection to the test traces on test board 1.
A.2 Types of trace constructions (figure A.2)
The preferred construction for the signal layers of the controlled characteristic impedance test boards shall be stripline, except that microstrip may be used where appropriate. These two construction types are defined as follows.
A.2.1 Strlpline construction means that the signal trace layer Is located between a pair of ground conductive planes, which serve as the high-frequency ground return conductors for the controlled impedance line (refer to figure A.2a).
A.2.2 Microstrip construction means that a signal grounded conductive plane near to the signal trace serves as the high-frequency ground return conductor of the controlled impedance line. The microstrip construction may be of either the surface microstrip type or the buried microstrip type which includes dielectric cover layers over the traces (refer to figures A.2b and A.2c).
A.3 Measurements with a resistive termination
For the sake of consistency, all measurements should be made with a resistive termination attached to the far end of the line being tested.
A.3.1 The value of this resistive termination shall be chosen to match the impedance of test board 3 (or test cable 2, as appropriate). Either an appropriate coaxial terminator or a discrete resistor of the nearest standard 2 % value may be used. If axially lead resistors are used, the lead wires should be kept as short as possible in order to reduce excess termination inductance. Wirewound resistors should be avoided for the same reason.
A.3.2 In order to reduce extraneous reflections, it is recommended that similar resistive terminations also be connected to both ends of any other test-connector signal lines, which may be strongly coupled electrically to the signal line being measured.
A.4 Calibration traces
Test boards shall include calibration traces for measuring the effective rise time and amplitude of the TDR system/pulse generator step signal, including the effects of the test fixturing, as well as the TDR/pulse generator signal source and sampling head rise times. Note that using this measured step amplitude for normalizing the connector reflections will automatically correct for the effects of any impedance level mismatch between the test equipment/cable, and test board 1. Either of the following calibration trace designs may be used.
A4.1 A straight-through transmission trace, which is twice the length of a typical connector test board trace, and provided with an identical coaxial cable or probe connection at both ends. In this case, the TDR/pulse generator system’s effective rise time and amplitude when used with this fixture board are determined from a time domain transmission (TDT) measurement of this calibration trace.
When the impedance of the test boards does not precisely match the impedance of the test equipment, a second portion of the waveform for measuring the effective test system amplitude and rise time is indicated in figure A.3.
A.4.2 A standard length test board trace terminated in a via which is shorted to the appropriate ground plane layers. In this case, the effective step signal rise time and amplitude for this combination of TDR!pulse generator and test fixture are determined as equal to the measured values of the amplitude and fall time of the negative step reflection corresponding to the short-circuit termination at the far end of this calibration trace, When the impedance of the test board does not precisely match the impedance of the test equipment and test cable, the falling transition from the zero reflection level to the short circuit or —1 p level includes additional positive or negative step portions. The recommended waveform portion for measuring the effective test system amplitude and fall time is indicated in figure A.4.EN 60512-23-4-2001 pdf download.