Wednesday, March 9, 2011

【 Weak current College 】 Protel software in high frequency circuit wiring skills 】


Digital devices is moving in a high-speed, low power, small size, high anti-interference, this trend on the printed circuit board design made a lot of new requirements. Protel software application in China has been quite common, however, many designers only concern to Protel software's "Chief pass rate", Protel software to adapt to device characteristics changes do improved did not used to design, which not only makes the software more serious waste of resources, but also makes a lot of new devices with superior performance is difficult to play. This article is intended to be used in high-frequency circuit wiring general introduction on request, to Protel for Windows V1.5 software as an example to introduce the high-frequency circuit wiring Protel software can provide some special measures.
(1) high frequency circuit is often integrated high wiring density, multilayer PCB is both a necessary wiring is also an effective means to reduce interference. Protel for Windows V1.5 provides 16 copper layers and four power layer, selecting layers can significantly reduce the size of plates, can take full advantage of the middle tier to set a mask that can better achieve the nearest grounding, can effectively reduce parasitic inductance, can effectively reduce signal transmission length can significantly reduce the signal crosstalk and so on, all of which are on the high-frequency circuit of reliable work. Have the same kind of material, the four-storey plate than the dual panel of low noise 20dB.  However, the higher the lamellar several more complex manufacturing process, the higher the cost. (2) high-speed circuit device PIN bending of the leader among the less the better. High-frequency circuit wiring of leader best full line, you need to turn the available 45 degree line or arc turn, such requirements in the low-frequency circuit is only used to improve the steel foil fixing strength, high frequency circuit, meet this requirement but can reduce the emission of high-frequency signal external and mutual coupling.  With Protel wiring is available in the following two pre-set, one is in the "Options" menu's "Track Mode" submenu of the booking to 45/90 90 Line or Arc/Line way wiring, the second is in the "Auto" in the menu "Setup" the Autorouter ... open Routing Passes "dialog box, select the" Add Arcs ", so that the automatic routing ends so that the angle of an arc. (3) high frequency circuit device PIN of the leader as short as possible. Protel meet minimum cabling is the most effective means is in auto City line before the individual focus on high speed networks for the "wiring" by appointment only. First, open the "Netlst" menu's "Net" submenu of the Edit, a "Net" dialog box, Change the dialog "OptimizeMethod (routing optimization mode)" selected as the "Shortest (minimum) to Rp."  Secondly, from the overall consideration, component layout in "Auto" and the "Placement Tools-Shove" Auto "in the" Density (density check) "to contrast adjust elements arranged in a compact and" Netlist "menu 's" Length "and" Info "menu selection" function, Lengthof on selected required minimum focus network wiring length measurement. (4) high frequency circuit device PIN leader among alternative less between layers, the better. The so-called "leader of alternating between the less the better" refers to the component during the connection process with through-hole (Via), the fewer the better, according to a survey, a hole can bring about 0.5 pF capacitance, reducing the hole number can significantly increase the speed. Protel software designed specifically to provide this functionality, it Auto menu Setup the Autorouter ... "to open the Routing dialog Passes", a "Advanced" section, the "Smoothing" is set to on. (5) high frequency circuit wiring to note that the signal cable close parallel alignment introduced "crosstalk", where it is not possible to avoid parallel distribution, parallel signal line reverse layout to "large" to substantially reduce interference. The same level of parallel alignment is almost impossible to avoid, but in the adjacent two-layer, the alignment of the direction must be taken as mutually perpendicular, this is not difficult to Protel but easily overlooked. In "Auto" in the menu "Setup Autorouter ... The open dialog box that allows Routing Lagers on each layer alignment direction intended for preselection of orientation: Horizontal, Vertical and "No", many users Prefer-ence accustomed choose "No Preference (no specific orientation)", is of the opinion that such a high rate of Chief Administrator, however, in the high-frequency circuit wiring in best in adjacent layers respectively take alternating horizontal and vertical layout. The same level of parallel alignment cannot be avoided, but you can reverse the plates to reduce the large area laying ground wire interference (this is a commonly used double panel, multi-layer boards can use intermediate power layer to achieve that functionality), Protel software only provides a simple "Fill" feature to meet this demand, now Windows of Protel addition also in the "Edit" menu of "Place" option offers higher placement Plane "Polygon", namely: polygon rasterization (MAL) copper foil surface, if you place it on the polygon with the entire surface of a plate, and the grid (bars) and GND circuit of network connectivity, then the feature will be able to achieve a monolithic circuit board side of the "shop copper", after "shop copper circuit board in addition to" improve mentioned high anti-interference ability, but also on the thermal, plate strength can benefit you, also, in the circuit board fixed metal chassis Department if the Tin bar, not only can enhance the strength, security contact fixed, can use the metal chassis constitute appropriate publicCollinear. In the software menu open the feature is visible to a "Place Polygon Plane dialog box, it will ask you whether you want to take the place of polygon rasterization (bars) and network connected (connect net), connected item, exit the dialog box will prompt you for the network name to connect to the given power GND network will be able to play the role of shielding layer. At the same time also will ask you "shop copper" pattern is a horizontal bar (horizonta), a vertical bar (vertica) or grid (both).  Choose the grid will have better shield effect, at the same time, the size of the grid network (referred to as the "eye habits") determines the basis to focus on shielding disturbance frequency. (6) on particularly important signal line or local unit implement ground surrounded by measures. The measures in Protel software can automatically, it is the "Edit" menu of "Place" under the "Outline Select-ed Items" that is: draw the selected object in the outer contour line.  With this feature, you can automatically on the selected important signal cable to the so-called "package" deal, of course, this feature is used to clock and other units to handle partial to pack on the high-speed system will also be very useful. (7) various signal alignment could not form loops, ground cannot form the current loop. Protel autorouting alignment principles in addition to the previously mentioned minimum principles, based on the X direction, based on the y direction and Daisy-shaped (daisy) alignment, use the Daisy-shaped alignment can effectively avoid the formation of loops while routing.  Specific to open ' Netlist "menu 's" Net "submenu of the Edit, a" Net "dialog box, Change the dialog" Optimize Method (routing optimization mode) "selected as a" Daisy Chain ". (8) each IC blocks high-frequency should be set up near a decoupling capacitor.  As Protel software to automatically place the component does not consider the decoupling capacitor and the decoupling of the relationship between the location of integrated circuits, software, so that they are too far decoupling effect compromised, then you must manually move the symbol ("Edit" and "Move" and "component") means the prior intervention both location, close to. (9) analog ground, digital ground, etc., to the common ground for HF choke points. In the actual Assembly HF choke link is often used when the center hole to wear with wires in high frequency ferrite beads, circuit diagram no expression to it in General, thus forming a network table (netlist) do not contain such elements, wiring will be ignored. In response to this reality, but in principle diagram as inductance, the PCB component library separately for it to define a component package, wiring before it manually moved to the join point near the public ground of suitable location.

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