Titelmasterformat TDR of a Connector durch with Klicken wiring Harness bearbeiten Christian Römelsberger (CADFEM GmbH) Ivan Vukosav (Yazaki) 1
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Aspects of Signal Transmission Information transferred by current or voltage Signals propagate with the speed of light Wires Wave propagation on transmission line guided waves. 3
Aspects of Signal Transmission Connectors are imperfections in a transmission line Transmission line Wires are separating The guided waves scatter on the imperfection of the connector leading to: Reflection of the signal Cross talk Leakage of radiation from the connector At high data rates high frequencies scattering can occur For good signal quality Design that avoids scattering No jumps in impedance! 4
TDR Calcultate TDR to detect jumps in impedance and their location Impedance different from 50 Ω 5
Telegrapher s equation Want to understand TDR in a more quantitative way! A transmission line model describes the propagation of a guided TEM wave quantitatively x In the continuum limit this leads to 6
Telegrapher s equation For constant c(x) and l(x) the solution for constant frequency is The propagation speed of the wave is v0. The impedance of the transmission line is Z0, this relates the voltage to the current. 7
Scattering along a transmission line Consider a jump in impedance of the transmission line at x0. A wave solution at a given frequency has the form Z 1, v 1 Z 2, v 2 Incoming wave Reflected wave x 0 Transmitted wave 8
Scattering along a transmission line The requirement that the voltage and the current are well defined at the interface at x0 leads to This relation makes it possible to determine the jump in impedance from the reflected signal. The frequency dependant phase relation allows to determine the position of the jump. Note that the ratio of the reflected voltage to the incoming voltage is the return loss 9
TDR The position of the impedance jump can easily be determined in the time domain from the reflected signal. If the incoming signal has the frequency content then the reflected voltage is 10
TDR The impedance Z2 is then This is used to determine the profile of the impedance of the transmission line. There are a few things to be noted here: The transmission line has to be terminated properly on both ends. A continuous change in impedance over the distance can be viewed as many small jumps. If there is a continuous change in impedance or many jumps, it is assumed that the reflections are weak enough such that waves are not reflected back and forth too much. 11
TDRZt(Diff1) TDR of the Connector In order to calculate a TDR with a rise time trise there has to be a frequency sweep up to 130.00 125.00 TDR Connector 120.00 Curve Info TDRZt(Diff1) Setup2 : Sweep 115.00 110.00 where n is the number of time steps per rise time. 105.00 100.00 95.00 90.00 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 Time [ps] >100Ω 100Ω >100Ω 100Ω >100Ω 12
Modeling the Twisted Pair For a rise time of 35ps this leads to frequencies of up to 70GHz, i.e. waves of a wave length as small as 4mm. For a twisted pair cable with a pitch of 11mm and a length of 1m it becomes computationally unfeasible to perform a direct field calculation of the TDR! 13
Modeling the Twisted Pair The strategy is to divide and conquer : A single pitch can easily be simulated in a FEM simulation using ANSYS HFSS. Many pitches can be put together in a system simulation using ANSYS Designer. 2_N 1_N Port2_N Port1_N Port2_N Port1_N Port2_N Port1_N Port1_N Port2_N Port1_N Port2_N Port1_N Port2_N Port1_N Port2_N 2_P 1_P Port2_P Port1_P Port2_P Port1_P Port2_P Port1_P Port1_P Port2_P Port1_P Port2_P Port1_P Port2_P Port1_P Port2_P 14
Modeling the Twisted Pair Determine the S-Parameter model of the 1m twisted pair in a linear network analysis 11mm 1m=91x11mm ANSYS Designer same NDE Nexxim State Space Model Scattering off a single pitch Cable Resonances 15
Putting Everything Together The TDR of the full system is determined in a transient system simulation inside ANSYS Designer: Nexxim State Space Model 100Ω Termination Differential TDR Probe with 100Ω Termination 16
Putting Everything Together From this system simulation one gets the TDR of the full assembly of connector with wiring harness on both sides There is reasonable agreement between measurement and TDR simulation for this large system! Measured 17
Which Parameters can be Adjusted? In reality, the cable has many uncertainties: The pitch p might not be exactly 11mm. The diameters D of the insulation and d of the copper have tolerances. In order to match the simulation results of the TDR of the twisted pair to the measurement, those parameters d, D and p can be adjusted. The units require that the impedance of the cable can only depend on ratios of the dimensions: In this way one can fix d. Assuming that the dependency of the impedance on the pitch is not too big, the pitch can be fixed. Now only d/d has to be adjusted in order to get the right impedance of the cable. D d 18
Which Parameters can be Adjusted? Parameters to adjust impedance Cable 3-5 parameters: Thickness of the conductor Thickness of the insulation How does the twisted pair open up to the connector pins Overlap of the pins Small overlap Big overlap Overlap Opening of the twisted pair 19
Effects of the Twisted Pair The incident signal is scattering off the turns of the twisted pair 1 pitch 20
Conclusions The ANSYS high frequency solution offers a very efficient way of simulating large wiring harnesses with connectors. In this methodology a set of building blocks can be set up using ANSYS HFSS: Connector Twist Bend Wires crossing Etc. In fast system simulations one can investigate S-Parameters Cross Talk Return Loss Mode Conversion TDR Impedance Intra-pair skew Propagation delays Signal Integrity Workflow can be generalized to determine emissions of the different single pieces 21
ANSYS HFSS supports our Design & Development and improves our Time2Market of reliable High-Speed-Communication Channels Ivan Vukosav, YAZAKI 22