This can be a standard guide on the ideal practice printed circuit board (PCB) style rules for a high frequency or radio frequency (RF) circuit. Following these guidelines will help you to prevent some of the most common pitfalls in RF style and design. Bad PCB layout is amongst the most typical leads to of inadequate transmit or get effectiveness and EMC failures as a result of spurious emissions. Ideally an engineer undertaking a PCB style really should be familiar with the IPC requirements as these supply a wealthy supply of info and best practice on the standard rules of PCB layout.
When planning to layout an RF PCB, the initial place to start off would be to get in touch with your favored board manufacturer and get a set of their guidelines and manufacturing abilities. This will likely include the minimum track and gap widths, drill sizes along with other crucial parameters. The board manufacturer need to also have the ability to provide you with their common layer stack and material data, this can contain the copper weights, dielectric consistent, plus the thickness of core and pre-preg layers in multi-layer boards. Unless your circuit is incredibly uncomplicated I propose that a four layer board is utilised this guarantees a steady ground plane. When working with a double sided board it truly is incredibly hard to guarantee the ground plane is un-broken. Yet another benefit of a four layer board is the dimensions with the micro-strip for any 50 or 75 ohm layout are more manageable. Use a micro-strip calculator to determine the expected track width to the style and design impedance and assure that it is in the manufactures abilities, if not chances are you'll ought to go over the layer-stack together with the producer and pick a non-standard build. An additional stage to note is in my expertise attempting to preserve separate ground nets for distinct signal area's ordinarily leads to troubles as an alternative to any benefit and is largely a throwback on the days prior to multilayer boards, a single low impedance ground plane is definitely the safest route.
It's fairly acceptable to work with FR4 for boards up-to 2.4GHz except if the highest level of performance is needed. In particular circumstances it truly is well worth specifying the board as managed impedance to provide constant RF overall performance.
Owning established the track and board geometries the following phase should be to deal with the element placement. Ensure that the RF parts are laid out this kind of that each of the RF tracks is often stored about the top surface with minimal length and alterations of route. Begin with reduced signal level places at the antenna or RF input and get the job done backwards towards the baseband or digital area. Hold digital and energy supply locations away from the analogue RF circuitry and continue to keep all of the RF parts on 1 side in the board.
Exactly where your RF tracks cannot be run in a straight line, use mitered bends in case your CAD procedure supports them, never use ideal angled bends on RF signal lines. If mitered bends will not be supported use a series of 45 degree bends or arcs, this minimizes impedance mismatches which would improve losses and spurious emissions.
On RF layouts it's popular to provide a ground flood on the prime layer and also to "stitch" this to the ground plane by utilizing several via's. When you intend to carry out this, assure that the copper is stored an appropriate distance through the RF tracks and components otherwise the impedance will likely be lowered and bring about additional harm than good. The by way of spacing may be 5-10mm apart there is incredibly tiny advantage in stitching via's getting closer than 5mm apart.
Tracks to ground from RF parts needs to be kept as quick as is possible and use 2 or three via's in parallel via's to lessen the impedance.
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