It is a basic guidebook on the best practice printed circuit board (PCB) design rules for any high frequency or radio frequency (RF) circuit. Following these rules will help you in order to avoid many of the most common pitfalls in RF style and design. Bad PCB layout is one of the most typical causes of inadequate transmit or acquire efficiency and EMC failures due to spurious emissions. Ideally an engineer undertaking a PCB style and design ought to be familiar with the IPC standards as these deliver a wealthy supply of info and most effective practice about the basic concepts of PCB design and style.
When arranging to layout an RF PCB, the first spot to start out is always to make contact with your preferred board producer and receive a set of their tips and manufacturing abilities. This may include things like the minimal track and gap widths, drill sizes together with other important parameters. The board manufacturer should also be capable of give you their common layer stack and materials data, this may consist of the copper weights, dielectric constant, along with the thickness of core and pre-preg layers in multi-layer boards. Unless of course your circuit is extremely easy I suggest that a four layer board is employed this assures a constant ground plane. When working with a double sided board it is actually very tough to ensure the ground plane is un-broken. Yet another advantage of the four layer board is the dimensions from the micro-strip to get a 50 or 75 ohm style and design are far more manageable. Use a micro-strip calculator to find out the demanded track width to the design impedance and ensure that it is within the manufactures abilities, if not you might really need to go over the layer-stack with the producer and pick a non-standard construct. A different stage to note is in my working experience attempting to keep separate ground nets for distinct signal area's commonly triggers complications as an alternative to any advantage and is largely a throwback on the days before multilayer boards, just one lower impedance ground plane is the safest route.
It can be really acceptable to make use of FR4 for boards up-to 2.4GHz unless of course the highest level of overall performance is needed. In particular situations it is actually really worth specifying the board as controlled impedance to provide constant RF functionality.
Getting established the track and board geometries the following stage is to deal with the component placement. Guarantee that the RF elements are laid out such that each of the RF tracks may be stored on the prime surface with minimal length and improvements of path. Start out with reduced signal level parts on the antenna or RF input and get the job done backwards in the direction of the baseband or digital region. Retain digital and electrical power supply regions far from the analogue RF circuitry and retain each of the RF components on a single side of your board.
The place your RF tracks can't be run in the straight line, use mitered bends in case your CAD process supports them, by no means use correct angled bends on RF signal lines. If mitered bends are usually not supported use a series of 45 degree bends or arcs, this minimizes impedance mismatches which would raise losses and spurious emissions.
On RF layouts it's prevalent to supply a ground flood within the leading layer and to "stitch" this on the ground plane through the use of multiple via's. For those who intend to accomplish this, make certain that the copper is stored a suitable distance in the RF tracks and elements otherwise the impedance are going to be lowered and result in much more harm than great. The by means of spacing is usually 5-10mm apart there may be very tiny benefit in stitching via's staying closer than 5mm apart.
Tracks to ground from RF elements should be stored as quick as you possibly can and use 2 or three via's in parallel via's to decrease the impedance.
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