Differential Pair Length Matching. As you know, there are two types of interfaces in PCB design and length tuning will be different for each of them. Because the longer trace, which isPick a signal frequency for your taper. The maximum PCB track length is then calculated by multiplying tr by 2 inch/nanosecond. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. As the trace length increases, this frequency shifts to the left, to 117. 1 Answer. 8 mil traces, and that is assuming no space. Loosely vs. The IC pin to the trace 2. UART. So the upper limit for the example given above is between 6in / 6 (= 1 in, ~2. This document focuses on. For instance, the topology may call for a daisy-chain route, which will increase the total length of the net. Quadrature coupler design can use discrete components or quarter-wavelength tuned traces to split or combine inputs and produce outputs with a 90°. t pd =š/šÆ6 Length Matching Overview The following sections discuss considerations for length matching. This variance makes Inside the length tuning section, we have something different. If you are to use a 1. 6mm spacing with a trace width of 0. If a short section of a 50 ohm cable has a 75 ohm impedance, then 33% of the voltage signal will be reflected at each end of the 75-ohm section. The switchback routing style (bottom left group of traces) provides a more compact link length compared to the serpentine style. The length of traces can cause problems with loss and jitter for LVDS signals. And, yes, this means generally using all 0402 components for that RF path. ;. Trace LengthTrace Length §Longer trace length ā loss ā ü~0. 54 cm) at PCIe Gen3 speed. This will be the case in low speed/low. Traces and their widths should be sized. 005 inches wide, but you may have specific high speed nets that need 0. FR-4 is commonly used for the dielectric material. $endgroup$ āIn particular, it will happen if you design a PCB and leave a short copper trace open-ended. 3. But given that length matching is required, it looks like everything you're doing is done as well as it can be. If you obtain component models from your manufacturer, the IBIS 6 documentation for the particular component should include the pin-package delay. Do you guys agree to this? mode voltage noise, and cause EMI issues. If you know about dispersion, then you know that youāll have to do PCB trace length matching vs. Remember, copper roughness increases the magnitude of the skin effect and creates additional lossy impedance. = Most PCB vendors will size traces for you You just tell them Z0 L0 is inductance per unit length C0 is capacitance per unit length. 56ns/m). It is sometime expressed as "loss tangent". That's 3. 3. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. 35 mm ā SR opening size: 0. However, I have a bit of a length mismatch between the TX+/TX- and RX+/RX- pairs (about 5mm). The loss increases linearly with the length of the PCB trace. Two of the traces have no reference plane beneath, and their lengths are Trace 1, 35mm, and Trace 2, 120mm. Hereās how length matching in PCB design works. Improper trace bends affects signal integrity and propagation delay. Proper interconnect design must account for the lower noise margins of. Configuring the Design Rules. a maximum trace/ cable length which is specified in the various specifications. I donāt often like to give answers in absolute terms to PCB design questions, but in this case the answer is clear: Never route a signal over a gap in a ground plane. How to do PCB Trace Length Matching vs. SPI vs. the series termination resistor is chosen to match the trace characteristics imped-ance. The extent of this problem will depend on the bus speed, the length of the traces, the trace geometries, the type of fiberglass weave used, and the alignment of the traces to the weave pattern of a PCB. The trace impedance or PCB impedance damages the integrity of both analog and digital signals. 2. Since my layer thickness is 0. As a thumb rule At what trace lenths should i used differential drivers (LVDS,RS485) etc for SPI interface. So the upper limit for the example given above is between 6in / 6 (= 1 in, ~2. For a parallel interface, we tune only the lengths of the traces. Added: On a real PCB, your signals travel slower than speed of light. The data sheet also describes the cables attenuation per unit length as a function of frequency. 5cm) and 6in /4 (= 1. cable length performance far exceeding IEEE specifications and features that provide lower cost solutions, for both 10BASE-Tand 100BASE-TXEthernet protocols, the devices ensure compatibility and inter-. My shortest signal needs 71*3. To achieve this, you may have to put small sections of trace tuning into the shorter line to equalize them. Figure 7: PCB traces with their parasitics ā circuit model and impedance vs. Most hardware problems with I2C come from having too much capacitance on the bus. Because trace, source, and load impedance mismatches are a critical concern in high frequency design, you need a PCB trace length matching vs. 7 and Ī¼ R ~ 1 for FR4 material. For timing constrained applications, always use the design software to ensure that the PCB traces in question are of the same length. This impedance is dominated by the physical separation between your power rails, traces, and internal planes in your board. Hereās how length matching in PCB design works. 2. 4 Implementing RGMII Internal Delays With DP83867The sections below describe these steps in more detail. The fact that the important quantity determining noise immunity is the signal timing mismatch has motivated the use of delay tuning for differential signals. The third trace has a solid reference plane beneath, and its length is identical to trace 2, 120mm. From there, component placement may be adjusted to better set up the high-speed trace routing required. Intra-pair skew is the term used to define the difference between the etch length of the + and - lane of a differential pair. This design issue becomes more critical with longer length traces on the PCB. This consists of maximum and minimum trace width, and length matching with other traces. This question (paraphrased) goes as follows: Do length-tuning structures create an impedance discontinuity? The answer is an unequivocal āyesā, but it might not. Matching the impedance can be accomplished by tying the trace down with a resistor near the source or the load. com PCB Trace Length Matching vs. 4 High Speed USB Trace Length Matching High-speed USB signal pair traces should be trace-length matched. While the lanes are not tightly synchronized, there is a limit to the lane to lane skew of 20/8/6 ns for 2. I2C Routing Guidelines: How to Layout These Common. Length Matching. I believe the mismatch of 3 cm in the examples above is not. The golden rule used in electronics is that you begin to have small problems when length mismatches are about one-tenth of the effective wavelength of the highest. Determine best routing placement for maintaining. Īµ r is the dielectric constant of the PCB material. Designing a PCB for PCIe Signals 11 Tsi381 Board Design Guidelines 60E1000_AN001_06 Integrated Device Technology Figure 1: PCIe Board Trace Width and Spacings Example 1. tions at the load end of the trace. The PCB trace width and the spacing to the grounded copper regions need to be designed to set the designed impedance to the. It is of fundamental importance that the traces with controlled impedance are appropriately spaced apart, as well as the other traces and the various components arranged on the printed circuit board. This is also done to avoid under or over-etching. The Altium auto router helps PCB designers with the difficult-to-master process of dense trace routing on a PCB. The exact trace length required also depends on. Design PCB traces with controlled impedance to minimize signal reflections. The basic idea of this length matching is that the shorter trace follows a detour or meander in order to lengthen it to match the length of the longer trace. As replied above my trace length varies between 35 and 57mm. High-Speed PCBs vs. For instance, the quarter wavelength (Ī»/4) of 433 MHz is 172. FR4 is a standard. Once the PCB has undergone this procedure, the configurations of the etching process and solution for the PCB has been determined to meet the desired impedance. For a single-ended trace operating at one frequency (e. Hereās how length matching in PCB design works. At the receiver, the signal is recovered by taking the difference between the signal levels on. For the signal trace of width W and thickness T, separated by distance H from a ground (or power) plane by a PCB dielectric with dielectric constant Īµr, the characteristic impedance is Impedance matching between copper traces is critical for differential routing and between the board materials for high-speed (frequency) signal transmission. For analog signals, the critical length (l c) is defined as one-fourth of the wavelength of the highest signal frequency contained in the signal. The need for multiple lines between the microcontroller and peripheral makes component mounting more of an issue and they should be placed as close together as possible to minimize trace lengths. 9mils wide. Calculate the impedance gradient and the reflection coefficient gradient. It seems like a rather simple task: connect a copper line from point A to point B with your schematic capture output as a guide. vias, what is placed near/under the traces,. Hereās how length matching in PCB design works. 203mm. Impedance mismatch: Impedance mismatches between the source, transmission line, and load can. The extent of this problem will depend on the bus speed, the length of the traces, the trace geometries, the type of fiberglass weave used, and the alignment of the traces to the weave pattern of a PCB. 192 mm gap shall be 100Ī© ± 10%. 25mm between the differential pair with a width of 0. frequency (no components attached). This variance makes Double data rate three (DDR3) is a type of dynamic random-access memory (DRAM) that succeeds earlier generations of DDR. At a foot length (300 mm), a signal frequency having this wavelength is about 1 GHz. Hereās how length matching in PCB design works. So unless you carefully design your routes within your PCB, the impedance would be uncontrolled, and its value would vary from point to point throughout the trace. Trace thickness: for a 1oz thick copper PCB, usually 1. between buses. CSI-2 (MIPI serial camera): The CM4 supports two camera ports: CAM0 (2 lanes) and CAM1 (4 lanes). High-speed USB signal pair traces should. I'm making a high-speed transceiver design and want some direction regarding layout of trace length from P to N. That is why tuning the trace length is a critical aspect in a high speed design. Here is how we can calculate the propagation delay from the trace length and vice versa: Where: Vis the signal speed in the transmission line; In a vacuum or through the air, it equals 85 picoseconds/inch (ps/in). PCB design software, like Altium Designer ®, has high-speed design functionality for routing and trace tuning built into it. Detangling the hair of a 9-year old doesnāt take as long as routing PCB traces, but the results are just as painful if not done correctly. If youāre a PCB designer, you donāt need to perform this calculation manually, and you just need to use the right set of PCB routing tools. Impedance profoundly impacts signal quality in high-speed PCBs. The world looks different, one end to another. SPI vs. Ensuring that signals arrive in time to process means that trace lengths may need to match. It may be convenient to use the same trace width across the entire design, yet it certainly isnāt optimal. SSTL 15 IO Standard (1) FPGA Side on-board termination(2. 5 cm or about 0. As I understand, the camera max frequency is 720 mbps, or 1380 ps of unit interval. I did not know about length matching and it did not work properly. Read Article UART vs. Read Article UART vs. 6 inches must be routed as transmission line. Wavelength of the highest frequency signal, š š¦ = šÆ/š š¦. Therefore, you must adjust the trace length for all parallel interfaces. ) and the LOW level is defined as zero. Table 5. SGMII vs. The ā3Wā Rule (s) This actually refers to three rules. However, while designing the PCB, I am not able to match all the lines from the connector to the controller. 7 = 404ps. For example: If you have 1 Amp going on a 6 mil wide trace of 1 oz copper for 1 inch of length, that's . SPI vs. This is the ratio of voltage to current as a wave propagates down the line. frequency because the velocity of the signal varies with frequency. SPI vs. ā¢ Within the PCB breakout region, use the following SMT recommendations: ā Ball-to-ball pitch: 1. Your design software provides the tools for selecting a terminating resistor value that connects near the source. 5Gbps. A trace has both self inductance and capacitance relative to its signal return path. Search for jobs related to Pcb trace length matching vs frequency or hire on the world's largest freelancing marketplace with 22m+ jobs. And the 100ps would be equal to 15-20 mm in trace length difference, which is huge. The above example does not mean that the PCB traces less than 1. Sorted by: 9. Jun 21, 2011 at 0:11. Trace Width (W) Figure 3. 008 Inch to 0. The DDR traces will only perform as expected if the timing specifications are met. My problem is that I find the memory chip pinout quite inconvenient. Whether the PCB maintains the balance will affect its functional performance status. For traces of equal length both signals are equal and opposite. First, adhere to the absolute routed maximums to prevent signal integrity issues. During that time, both traces drive currents into the same direction. Is this correct? a. PCB trace antennas at lower frequencies,For my results, I find that the minimum inductance is 292 nH per meter when ( w/h) = 1. ) of FR4 PCB trace (dielectric constant Er = 4. 3 can then be used to design a PCB trace to match the impedance required by the circuit. Trace length matching; To know more about PCB routing read our article 11 Best High-Speed PCB Routing Practices. Once upon a time, length matching guidelines for high-speed signals required a designer with enough skill to remain productive when manually applying different trace-length turning schemes. 4 High Speed USB Trace Length Matching. Today, PCB designers are spoiled with CAD tools that make it extremely easy to apply length matching sections to a differential pair. Tip #2: Board Stack-Up. Call Us. Note: The current of the signal travels through the. A more. Trace Length Matching vs. frequency can be reduced to a single metric using an Lp norm. Would a 2-3 cm difference in lines beget problems?Critical length depends on the allowed impedance deviation between the line and its target impedance. 5in, ~4cm) for a trace on a PCB with a dielectric constant of 4. Observation: A 3cm microstrip and a 3cm stripline can get a very different propagation delay! Conclusion: If we would route a bundle of traces, eg. About a year ago I designed a PCB with a processor and RAM (400MHz and 133MHz speed respectively). Generally, PCB trace thickness ranges from 0. This will help you to route the high-speed traces on your printed circuit board pcb to the correct lengths without having to guess their actual lengths. Test Setup The cable used for this investigation was category-5 Belden MediaTwistā¢. 015 meter or 1. 1How to do PCB Trace Length Matching vs. It would be helpful to know the tolerance in length difference that is allowed while designing this PCB. I am more interested in the impedance, reactance and resistance of traces in my question for given frequencies in pcbcad softwares for a given layer stackup than the antenna shapes. Follow asked Nov 27, 2018 at 12:32. If we were to use the 8. High-speed PCBs operate in the range of. Clock frequency < 18 MHz <=> Period > 55 ns. Controlled impedance boards provide repeatable high-frequency performance. They are simply the traces on a PCB and depend on the length and the frequency of the signals passing through them. On theseFor a given PCB laminate and copper weight except for the width of the signal trace (W), the equation given below can be used to design a PCB trace to match the impedance required by the circuit. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. Short Traces and Backdrilling. If the length of the interconnection is greater than or equal to Ī»m/12, then the PCB must be designed as a high-speed PCB. traces may be narrower for stripline routing. For RF signals at high-speed, the integrity can take a hit (if not designed correctly) at approximately 50 MHz or. It would be helpful to know the tolerance in length difference that is allowed while designing this PCB. Hereās how length matching in PCB design works. This might or might not be an issue, as we will see in a minute, because it all depends on the signal frequency and trace length. How to do PCB Trace Length Matching vs. The flex cable to TOSA (ROSA) elements At point 2, the reflection is primarily generated by the PCB layout. Route each RGMII signal group (transmit group ā (GTX_CLK, TX_EN, TXD[3:0]); receive. Rule 5 ā Match the trace length. The guidelines are based on best practices and TI reference designs for high-performance and reliable PCB design. 1. Opting for longer traces may be a better choice, but pay attention to a transition to transmission line behavior as the trace length is increased. 2 Stripline Impedance A circuit trace routed on an inside layer of the PCB with two low-voltage refere nce planes (such as, power and / or GND) constitutes a stripline layout. PCB Trace Stubs and Discontinuities ā¢ If possible, avoid routing high-speed frequency traces through the vias. 3 High-Speed Signal Trace Length Matching Match the etch lengths of the relevant differential pair traces. If the line impedance is closer to the target impedance, then the critical length will be longer. 005 inches wide, but you may have specific high speed nets that need 0. Whether you see a specific length specified or a time specified, either value will only apply for a specific PCB laminate and trace geometry. Probably the most common electrical uses for LVDS are as an physical layer for SerDes links, long-reach channels in backplanes, or board-to-board connections. It's free to sign up and bid on jobs. Intra-pair skew is the term used to define the difference between the etch length of the + and - lane of a differential pair. Impedance matching on a PCB involves designing transmission lines with consistent width, spacing, and dielectric properties. You can use 82 Ohms / 43 Ohms pair. This, in turn, enhances the signal quality and minimizes signal loss. For any distance over which I2C is a viable means of communication, and certainly within a single PCB, there is no need for any trace length matching constraint between SCL and SDA. In Figure 2, you can see that the transmitter waveform consists of data bits of longer duration (lower. Figure 1. The RS-485 protocol standard allows up to 32 drivers in one system, supporting communications over distances of up to 1200 meters, and can keep baud rates from 110 Baud to 115200 Baud. More important will be to avoid longer stubs. 7 dB to 0. Keep the spacing between the pair consistent. 0 and 3. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. What Are Pcb Traces Assembly Yun. Following the 3W rule can. Hence, I am employing the "squiggly line technique" to minimize the length mismatch of. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. As I. DKA DKA. Therefore, their sum must add to zero. How to do PCB Trace Length Matching vs. Length matching for high speed design . Technologies DDR3 Routing Topology Page No #5 DQ/DQS/DM:If a transmission line has a 50 ohm impedance, then connecting it abruptly to a 1 V source will cause a 1 V voltage wave and a 20 mA current wave to start travelling along the line. To ensu re a robust interface, the designer must address both components. However: The Raspberry Pi Computer Module 4 (CM4) datasheet states: 2. Trace Length Matching : This allows the user to. Vendor may adjust trace widths, trace. How to do PCB Trace Length Matching vs. Impedance in your traces becomes a critical parameter to consider during stackup. How to do PCB Trace Length Matching vs. Broadly speaking, I understand that PCB trace length matching is important from signal timing and signal integrity point of view, but I want to know some more specifics about these two parameters and. Taking away variables makes the timing and impedance calculations simpler. In contrast, for an internal trace with the same dielectric material we need the trace to be less than 10. Frequency with Altium Designer. For the signal trace of width W and thickness T, separated by distance H from a ground (or power) plane by a PCB dielectric with. The higher the interface frequency, the higher the requirements of the length matching. Below ~5GBps not something to worry about at all. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. This characterstic impedance is independent of length and trace material, depends on substrate thickness and trace width, and is usually in the 50 to 100 ohm range. These traces can be made of materials, typically copper, and are designed to have specific widths and thicknesses to handle different current loads. Well, if you manage to get 50 Ohm trace for this LCD on a 2-layer board with meaningful trace widths please find me :) I hope you are aware of the fact that the PCB thickness should be very low. How to do PCB Trace Length Matching vs. So I think this 100 MHz will define the clock edge rise/fall time. On theseselected ID and PCB skew. 6 USB VBUS The TPS2560 is a dual channel power distribution switch that can handle high capacitive loads and short circuit conditions. The bends should be kept minimum while routing high-speed signals. The board thickness and trace width and thickness should be adjusted to match the impedance. I then redesigned the board with length matched traces and it worked. Tolerance - specifies a length tolerance when comparing each net with the longest net in the set. 1 Ohms of resistance. At an impedance mismatch, a portion of the transmitted signal isFigure 3. 7cm. Minimize trace length and bends: Long traces can introduce. 1. Keep the total trace length for signal pairs to a minimum. How to do PCB Trace Length Matching vs. 1V drop, you need to obviously widen the trace or thicken the copper. Some possible changes include the addition of termination components, careful design of impedance matching networks, or redesigning traces to adjust their impedance. With todayās technology, Fast Ethernet (100BASE-TX) and Gigabit Ethernet (1000BASE-T) are. Hereās how length matching in PCB design works. For most manufacturers, the minimum trace width should be 6mil or 0. SPI vs. 2. USB,. I2C Routing Guidelines: How to Layout These Common. I2C Routing Guidelines: How to Layout These Common. I did not know about length matching and it did not work properly. In this article, weāll examine a few tips and tricks for high-speed printed circuit board designs. Single-ended signals are fairly straightforward. How tightly should trace lengths be matched for a 1Gbps serial databus? It seems to me that 100ps (15mm) should be more than sufficient. There are a few termination techniques that you can use to ensure high-speed signals on your PCB suffer from no reflection or distortion on the trace. Trace length-differences can be a problem when signal propagation delay through the length-difference is a significant part of the clock period. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. PCB Trace Length Matching vs. The output current for each channel can be adjusted up to 2. However, it rarely causes any problem at low speeds. Would a 2-3 cm difference in lines beget problems? Critical length depends on the allowed impedance deviation between the line and its target impedance. 2. 1uF, and 1. 1 Ohms of resistance. To ensure length. Hereās how length matching in PCB design works. PCB Radio Frequency Testing. SPI vs. I2C Routing Guidelines: How to Layout These Common. Tip #3: Controlled Impedance Traces. When these waves get to the end of the line, they may find a 50 ohm resistor. But to have some tolerance, we generally. 2) It will be vise to match the PCB trace impedance to the cable impedance, or you may get reflections. Length tuning and delay tuning basically refer to the same idea; the goal is to set the lengths of signal traces in a matched group of nets to the same length value. Read Article UART vs. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. For most JTAG, SPI, and I2C communication it is probably unnecessary, as these speeds tend to be fairly slow. 25 to 0. By controlling the PCB impedance, unexpected damages or errors can be limited to some extent. How to do PCB Trace Length Matching vs. 4 mils or 0. Ideally, though, your daughterās hair isnāt causing short-circuiting. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. 4 Implementing RGMII Internal Delays With DP838671. For the signal trace of width W and thickness T, separated by distance H from a ground (or power) plane by a PCB dielectric with dielectric constant Īµr, the characteristic impedance isThe list above is not exhaustive, as trace routing is also a special consideration for communications boards. However, you don't always have the freedom to place. In that case I need to design a transmission line which has characteristic impedance of 50. 7 mil width for the rough. The trace length decided to match with Wavelength of the frequency Wavelength (Lambda) = Wave Velocity (v) / Frequency (f) =299792458 /700000000 =428. 3 Length and length matching Trace length greatly affects the loss and jitter budgets of the interconnection. 25mm trace. 5 GHz. It leads to either: - rising edges on SCL become too slow, which means the signal spends a lot of time around the receiver's 0/1 threshold. Lower-frequency trace antennas are challenging from a size perspective because the design demands quarter wavelength structures with ground plane to support effective radiation characteristics. PCB Antenna 3. 35 dB to 0. 254mm wide and trace seperation to 0. 425 inches. Select a trace impedance profile over the length of the taper. According to these. Tuning a trace with serpentine routing in OrCAD. , RF signals), it's okay if you only know the value of the dielectric constant at a single frequency. They recommend 3 times the trace width between trace center and trace center, until here all ok. SerDes PCB Layout Guidelines: This means we need the trace to be under 17. Read Article UART vs. Again, this ideal length for the clock is found by subtracting the tolerance (or most of it) from the longest trace once everything is optimized. Note2. Hereās how length matching in PCB design works. Matching trace lengths at specific frequencies require. Coplanar waveguides are open quasi-TEM waveguide geometries that use copper pour and a ground plane to provide shielding along the length of a PCB trace. Frequency Keeping high speed signals properly timed and synchronized requires PCB trace length matching vs frequency. Microstrip Trace Impedance vs. Spacing and width value pairs that will give a differential impedance of 100 Ohms on Dk = 4. The most common approach is to design your microstrip or CPWG to match the component pads for devices in the path. Hereās how length matching in PCB design works. In particular, the transit time of signals often needs to be synchronized by matching the copper length of the traces on the PCB. SPI vs. With today's advanced interactive routing features in modern PCB design tools, designers no longer need to manually draw out length tuning structures in a PCB layout. This is a general PCB layout guideline for ISSI DDR4 SDRAM, especially for point-to-point applications. Set up your differential traces for success. This 6-layer PCB stackup can enable orthogonal routing on L1/L3 and on L4/L6. rise time (tRise). As the frequency increases, PCB traces behave like transmission lines, with a precise impedance value at each point on the trace. The length and Z o affects path loss and special delays with frequency/length ratios like 1/4 wave impedance reflections (inversion) and all odd harmonics of same. 00 mm ā Ball pad size: 0. Characteristic impedance of all signal layers to be 50 Ī© ± 10%; Differential impedance of 0. In summary, we have shown that using the Lp norm can reduce PCB board trace length matching versus frequency to a single metric. Hereās how length matching in PCB design works. ā¢ Narrower DDR3 output drive ranges that can be recalibrated to adjust for voltage and temperature variations. 3) Longer traces will not limit the. The lines are equal in length to ensure impedance matching of the signals. Impedance control. If your PCB has the space, why not match the lengths? It's good to practice length-matching any time you have the chance. rinsertion loss across frequency on the PCB. 3. The longest track is shorter than 1/5000 of a wavelength. Trace routing is one of the critical factors in constraint settings. Configuring the meander or serpentine style in the Proteus. Design rules that interface with your routing tools also make it extremely. 010 inches spacing between them. And the specication says the GPIO clock for the PRU is 100MHz. Here's how I do equal length differential pair routing in Eagle CAD: Name traces D_P and D_N (or something _N and _P - seems like Eagle CAD needs the suffix). ā¢ Provide impedance matching series terminations to mini mize the ringing, overshoot a nd undershoot on critical sig-nals (address, data & control lines). By default, most PCB design programs with length matching capabilities will set the pin-package delay to zero length or zero time.