usb differential pair trace width

I thought about calculating it myself manually, but when I looked at the equations I was a bit lost. Line width/cross-section Air gap Length Uncoupled Length Anything else in the vicinity Trace geometry (width, thickness) and air gaps are the drivers for impedance. See the following Managing Differential Pairs section for more on the Differential Pair dialog. At the other extreme, the long channel connects the USB device to the controller through a 3 meter long cable. dear friends I want to route 100 ohm differential pairs of LAN on two layer pcb ( 1.6mm pcb thickness ) with 8 mil trace width, 8 mil trace spacing , 1.4 mil trace thickness. Width of the trace and height of the dielectric can be adjusted as needed. However, good design practice is to route USB signals as an impedance Gloss preserves the existing trace width and differential pair gap. PCB manufacturers will also test impedance for you before the boards leave their shop. dsandber wrote:Anyone know the recommendations for differential pair impedance for the USB. As an example, consider a differential trace pair on Layer I that is 8 mils (0.2 mm) wide and 2 mils (0.05 mm) thick, with a spacing of 8 mils (0. . If necessary, a TDR test can be performed to check that impedance is correct. For other board sizes, check with your PCB manufacturer for the proper PCB stack-up, line width, and line spacing. As explained in Part 1 of this series ( Circuit Cellar 367, February 2021 [3]), PCB manufacturers can propose different PCB stack-ups, and specifying a low thickness for the so-called "top prepreg" will help to reduce the trace width. How to route Differential Pair: 1.Set the Differential Pair net name as XXX_N, XXX_P or XXX+,XXX-, and set the rule for the Differential Pair net at the "Design Rule". Isolate different USB differential pairs . (dielectric constant Dk=4.3 as fr4 material with 1.6 mm is used) can anybody help me how to calculate 100 ohm impedance. Also, maintain a minimum keep-out area of 30 mils to any other signal throughout . Unlike single-ended signals, differential signals take advantage of not one, but two traces that work in tandem together. 3. Hi All, I am new to Eagle (previously working with Altium). S1 is the spacing within a differential pair. It's quite possible that the layer spacing is, in fact, 1.6mm. A good rule of thumb here is Gap = 3 x trace width. Differential Pair Routing. The GND plane should be one solid extent. . You then need to change the name of your nets, so Autodesk EAGLE recognizes them as differentials. External traces: I = 0.048 x dT0.44 x A0.725. See the below image of the USB signal coming from the USB port to the targeted component that uses the USB signal. >> the trace width. Example length tolerances include high-speed USB, length mismatch should be no greater than 150 mils; DDR2 clocks need to be matched to within 25 mils. each trace of the pair will experience different dielectric constants and corresponding signal velocities due to the differences in static permittivity (r) of the Differential signaling is commonly used in many communication protocols, including RS-422, IEA-485, Ethernet (via twisted-pair wiring), DisplayPort, HDMI and USB, as well as on PCBs, where the . You'll then apply the net class you created in Step 1 to each of your nets. The information that is transmitted, is not only embedded in the signal amplitude but also relies on that phase shift. According to IPC-2221A Par. This video shows you how. It's for a 2-layer 1.6 mm board. So, with the routing tool still activated, Right-click > Select Via/Track Width > Use Custom Values Change the trace width to your default (e.g. It's often stated that the traces in a differential pair must always be spaced close together. The PTN3222 eUSB2 and USB2.0 differential pins are optimized to allow direct PCB routing to eUSB2 host/peripheral without any via. However, when the USB device works at 480 Mbits/s, it is not enough to do the above. The trace width can then be calculated by re-arranging this formula to determine the cross-sectional area that . To transfer a differential signal between two points, besides the ground return, you need a differential signal pair, thus two traces. Remember, the trace width on a standard thickness PCB with two layers was about 110 mils for Dk - 4.8. Figure 4. To control crosstalk, keep aggressors far away from differential pairs, especially on Microstrip (outer layers). Yes, and the substrate height is wrong in the calculation input. For example, with a thickness of 0.25mm, a trace width of 0.35mm gives 50, far easier to use. DP Universal Serial Bus (USB) 2.0 differential data pair, positive DM Universal Serial Bus (USB) 2.0 differential data pair, negative . Both D+ and D- are 12 mil traces as well. One line carries the signal while the other line carries a complementary, equal, and opposite image of the signal. Click Route > Route Differential Pair. USB specifies a minimum rise time of 4 ns, which equals a maximum signal bandwidth of 87.5 MHz or a minimum wavelength of 1.7 meters on a typical PCB trace. In this case, the electromagnetic coupling between them will create large mutual inductance and mutual capacitance. DP/M USB 2.0 differential data pair SSTXP/N,SSRXP/N SuperSpeed differential data pair SATA_RXP/N, SATA_TXP/N . These mean that the width of the serpentine(B . Both tolerances are +-15%. PCB References 2. I am working on a PCB design (6 layers with layer 2 and 5 as power-planes while 3 and 4 as signal layers) having speed differential traces. The width, spacing, and thickness of the routing need to be matched in such cases. To maintain trace impedance, the width of the trace should be modified when changing from one board layer . However, this does add some additional cost. You should see the pairs in the spreadsheet, they will have a + to the left of their name indicating this particular diff pair has 2 nets. Contact your PCB manufacturer in order to get the information about the resulting width W2. When the two traces are designed with the exact same impedance, then taking the differential impedance and dividing by 2 gives you the odd-mode impedance value of each trace: Odd-mode impedance defined in terms of differential impedance. The test sample consists of a pair of differential traces at the top layer, followed by a differential via to the inner traces, then a second differential via connects to the BGA landing pads at the top layer again. When you route them it will be routed as differential pair. The board stack (OSHPark) is as follows: 1 mil solder resist 1 oz copper (1.4 mil) 6.7 mil prepreg Where I is maximum current in Amps, k is a constant, dT is temperature rise above ambient in C, & A is cross sectional area of trace mils. In high-frequency systems using differential pairs, unbalanced currents, or ground currents, take the path with the least impedance. I imported the PCB files and when I perused the USB differential pair, first thoughts are this is not right. If during the routing, you wish to route it as individual traces, just click on the trace -> right click -> Select . is 6 mils and the distance between the differential pair(A) is 8 mils. with a calculated trace width of 6 mils requires a minimum of 30 mils spacing between high-speed differential pairs. Try to keep all other high-speed traces at least I have started routing the 90R controlled impedance tracks for the USB. Differential pair impedance defined in terms of odd-mode impedance. Ordinary USB device differential line signal line width and line spacing can be consistent with the entire PCB board signal line width and line spacing. Differential pairs should be routed away from all other traces. When routing PCB traces, it is critical to keep the trace width the same to keep the trace impedance constant from the driver and the receiver . As I pointed out in the previous blog, you can't use the trace width corresponding to the characteristic impedance in High Speed USB 2.0 and still meet the impedance spec. . Waveguide 1B1A Example Figure 5. To get the correct parameters, we have to use the specifications from our PCB house and the provided calculator. Figure 4. ; To minimize reflection noise, place the . Differential signal also means that the signal traveling on the traces are 180 out of phase. With that, the length of the traces should be equal in each pair with a tolerance of Y mm, given that Y < X. Aligning of the traces' lengths leads to the loss of the distance equality between the tracks of a . Edge coupled differential pairs - traces are adjacent to each other in the same plane with tightly controlled width and spacing, ground plane optional. After you created the pairs under the logic menu, open the constraint manager and go to > Electrical > Net > Differential Pair worksheet. What Differential Signaling Is All About. I heard D1_P and D1_N needs to be short to enable the flipping feature. Internal traces : I = 0.024 x dT0.44 x A0.725. All of my differential pair traces were under 50mm on this board. It is a four layer board. Regarding the impedance of USB signal traces the layout guidelines state: DP, DM Differential trace impedance = [DP (45ohm) + DM (45ohm)] = 90 ohm, and do not jump the DP DM signals that cause impedance miss match To meet those requirements I used some online impedance calculators to estimate the required trace properties for a 2-layer FR4 PCB. The spacing between two USB 3.0 differential pairs and a USB 2.0 differential pairs should be 20 mils or implemented with ground plane. Design Techniques for DDR, DDR2 & Left-click again to start routing the trace. The topology pre-dates the solid-state era and is generally attributed to Alan Blumlein, when it appeared in one of his patents in 1936. putting these values in the online calculator I end up no where near the 100-110 ohm that is specified for the camera lanes and USB. 0.2 mm for me). In addition, the traces on the printed circuit board are routed at the maximum length (approximately 10") and may contain multiple layer-layer transitions using through-hole vias. This pair is now a differential pair. you can determine the impedance between the differential pair. In the layout tool, the traces have to be designed with a width of W1. According to this guidelines, the differential pair (DP and DM signals of the USB) must have 90 ohm impedance to each other. The differential via design shown in Figure 2 was built and tested. This is the experience for Samtec twinax eyespeed cable and may not be the experience for all cable suppliers. This will create the differential pair. To be precise, the current flows through the . be made with trace width, dielectric thickness or relieving of metal on adjacent layers to compensate for additional needed thickness above or below the trace (as shown in the 2B2A example). The trace spacing between SuperSpeed and Hi-Speed signals should be 8 mils. Such a microstrip is constructed with two traces referenced to the same reference plane with a dielectric material between them. I've got the information from the manufacturer to use a trace width of 0.22mm and trace spacing of 0.125mm to achieve 90R impedance. Changed the Internal Asymmetric Differential Pair formula for better accuracy. By specifying the trace width, spacing between the traces, copper thickness, etc. The loss difference between 85 and 100 ohms is as much as 14%, and is explained in the actual geometry of the twinax. Log in or register to post . Before we can start routing the PCB, we need to define Design Rules for our differential traces. This yielded like 150 ohm impedance, not 90 or 100. EFM32 microcontrollers do not support operation as a USB hub. Comparison of 4-4-4 mil geometry (left) vs. 3.35-4.65-3.35 geometry (right) to achieve 100 Ohm differential impedance for the same center-center pitch. One of the features of this type of microstrip is the coupling between lines. In order to get 100 Ohms differential, the line width must be reduced to 3.35 mils and space adjusted to 4.65 mils to keep the same 12 mil center-center pitch, shown on right. I would like to route them on internal layers (3 and 4). Max trace-length mismatch between high-speed USB signal pairs should be no greater than 150 mils. High-speed USB signal pair traces should be trace-length matched. . http://go.web.cern.ch/go/fK9TA demonstration & tutorial of differential pair routing & trace length match. My miscalculations had me routing between 8-10 mil wide traces, with a 8-10 mil gap between the pairs, and 25 mil spacing to the ground pour and other signals. You first need to create a new net class that you can use to apply width rules to your differential traces. I am attaching the schematic and board layout. Specify the minimum line spacing, Primary Gap & Primary width. Right-click on a Differential Pair entry in the PCB panel then select Properties (or double-click on the entry directly) to open the Differential Pair dialog in which you can view/modify the properties for differential pair name and its constituent nets. A is the cross-section area [mils 2], I is the maximum current [A], T RISE is the maximum desired temperature rise [C], W is the trace width [mils], T is the trace thickness [oz/ft 2], k, b and c are constants. The total trace length for D+ and D- is about 10000 mils. With CES we also have access to HyperLynx stack-up editor which allows us to determine single-ended and differential pair trace widths and gaps for impedance controlled nets ( Figure 2). Differential pairs should be constructed as 100 ohm, controlled impedance pairs. The spacing between D+ and D- is 60 mils and the distance from D+ to VBUS and D- to VBUS is 24 mils. 4. You should enter the height of the outer layer, presuming you have a ground plane in layer 2. Here's how it works - you've got two traces that both carry the same signal, one of which is considered the positive signal, and the other trace is considered the negative . To minimize crosstalk, do not route the signal traces between the SSTX/SSRX/D pairs close to each other. But I am not able to match this impedance. The traces should be symmetrical. As your designs speed up, you might need to use differential pairs for higher speed signaling. The trace width is then adjusted to achieve the neces-sary impedance. 2.Click the menu Top Menu - Route - Differential Pair Routing. I tried using different line width (10mils,15mils,20mils,25mils,30mils) of the differential pair but it doesn't help me. We can summarize that, theoretically, in differential pairs, there are two return paths: the adjacent trace (trace 2) running parallel to trace 1 and the ground plane. Route the differential pair traces parallel to one another and as close as possible. 3.Click the one pad of the Differential Pair pads. The traces have a trapezoid form due to the etching process. PCB Layer Trace Net Name Top SS Differential Pair Trace (Hub IC should be placed in the same layer) Bottom HS Difference Pair , Control Signal 2.3 Differential Pairs Trace 2.3.1 Differential Pair Impedance The differential impedance requirement must be 90 Ohm 10 % and trace width / spacing may be different A USB capable EFM32 microcontroller can operate as a host, a device or as an OTG dual role device. Differential signaling transmits information down a pair of coupled traces on a PCB. Against the two rows select the required Referenced Spacing Set, you created in step 2. Step 2 - Define Your Net Names. Match the etch lengths of the relevant differential pair traces. If you are not able to get a plane close enough (4mil - 2 times the trace width) I will suggest route G-N-P-G or G-S-G on the same in order to give the HS Signal a return path. Step 3 - Apply Your Net Class. The difference seems pretty severe (10%) but I guess would fall within the 25% tolerance, so it might be OK either way--I don't know. 2.5 High Speed USB Bias Filter AT85C51SND3Bx high-speed USB design requires a 6.81KW 1% resistor in parallel to a 10pF capacitor connected from UBIAS pin to USB ground. Trace width is 0.25mm (9.84 mils), and space is 0.2mm (7.87 mils). Try to fan away evenly from the pads, avoiding 90 bends. Figure 2 - HyperLynx Stack-up Editor This will cause the single ended impedance of a trace in the differential pair to be different from the characteristic impedance. The EFM32 USB stack supports host mode and device mode, but not OTG mode. It is permissible to swap the plus and minus traces on one or both of the USB 3.0 differential pairs. When routing the differential pair, always balance the traces; . Now, you may not have room to route 30mil traces for your USB lines, but it is possible. To use this tool, enter the values for . Therefore, it is strongly recommended to not place any via in the path. The length of one trace of each differential pair should be as same as possible with another trace. Its utility stems from its ability to . To get 100 ohm in need to use a four layer PCB ( height to ground plain 0.3mm ) Use 16 mil width trace with 6 mil spacing ( I can't go lower then that ) , with a 35um trace thickness. In addition, the routed length on the device may be We also need to control the impedance of the differential signal. USB 90ohm Differential Pair Track Impedance USB 2.0 requires 90ohms differential impedance (max 45ohms per track) Max trace-length mismatch between High-speed USB signal pairs should be no greater than 3.81mm. The line width of each trace should be 0.4 mm, with 0.18 mm of space between the traces. there's nothing to indicate that the overall board thickness is 1.6mm or 3.2mm or . My trace calculator (in KiCAD) tells me that a trace spacing of 6mil and a trace width of 30mil gives a differential impedance of about 90ohms (at 1.6mm FR4 PCB thickness and 1oz/ft 2). Routing the traces establishes a balanced transmission system that carries the equal and opposite differential signals across the PCB. ; Make sure D > 2S to minimize the crosstalk between the two differential pairs. Best Technology have a simple excel file can calculate the impedance control and you can also send your Drawing, stack up so that we can calculate the exact impedance control using the . Note: Use the following guidelines when using two differential pairs: D = Distance between two differential pair signals; W = Width of a trace in a differential pair; S = Distance between the trace in a differential pair; and H = Dielectric height above the group plane. That is, higher impedance cable has less insertion loss whereas higher impedance PCB would otherwise be more loss. 4. Ideally, this trace width to height above the ground plane ratio is between 1: 1 and 3:1. I length matched all pairs to within 1mm. 6.2 ("Conductive Material Requirements"), their values for inner layers are as follows: k = 0.048 b . computer as a USB Mass Storage Device, or act as a host if a memory card reader or a USB memory stick is connected. W2 depends on the trace height (T1) and the duration of the etching. As per impedance calculations, differential traces width and clearances are different for outside and internal layers. Let's calculate the trace thickness and trace spacing-Som with a 15% tolerance and 90 Ohms targeted impedance, the conductor width required 0.254mm, spacing between both is required 0.127mm. The GiGE port has a worst case mismatch of over 255 mil in a differential pair and over 660 mil of pair to pair mismatch, and still passed CE Mark emissions with 18 dB of margin. DP USB 2.0 differential data pair, positive DM USB 2.0 differential data pair, negative SSTXP SuperSpeed differential data pair, TX, positive . For example the distance between conductors of a >> differential pair for a w = .005" wide trace with a separation of .005" >> (h=.010" center to center) and an Er = 3.5 is 45.12 Ohms. The trace between the D+ and D- is VBUS, and it runs between them for 2000 mils. Thus if PCB traces are shorter than 170 mm, it can be argued that the characteristic impedance of a track is not important. Route the differential pairs to impedance and at the optimal spacing: Gap = 2 x trace width. This is a 1.6mm board. Note that outer layers are the ones where it is harder to know the final copper thickness so more variability should be allowed for when using the outer layers extensively. The 100, 90, and 50 Ohm classes allow us to define trace width impedance rules based on layer, simplifying routing. This along with the Internal Symmetric Differential Pair formula and still under review and need to be changed but they are both within an acceptable tolerance now. . One caveat is that design does have some odd shielded Cat5e cables inside the enclosure (3" of cable with 1" of shield in the middle with 1" pigtails on each end). Retrace - assumes the overall geometry is satisfactory, focusing instead on verifying that the routing meets the design . Length matching rules for differential pairs are more complicated. DONATE to Kicad Development (Paypal now available!) This calculator is designed to calculate the characteristic impedance of an edge-coupled microstrip. So, a good amount of Impedance control knowledge is required. So in this case, >> keeping two traces as close together as possible with .005"/.005" design The differential pairsometimes called the long-tailed pairis a widely used building block in electronic circuits, particularly in op amps.