This can be a basic guidebook to the most effective practice printed circuit board (PCB) design principles to get a substantial frequency or radio frequency (RF) circuit. Following these rules can help you to avoid a number of the most typical pitfalls in RF layout. Bad PCB layout is one of the most typical leads to of inadequate transmit or obtain functionality and EMC failures as a consequence of spurious emissions. Ideally an engineer undertaking a PCB style should be accustomed to the IPC standards as these present a rich supply of facts and most effective practice about the common concepts of PCB layout.
When setting up to layout an RF PCB, the primary spot to start is always to contact your preferred board manufacturer and obtain a set of their guidelines and manufacturing abilities. This may include the minimum track and gap widths, drill sizes and also other essential parameters. The board producer should really also be capable of provide you with their common layer stack and material data, this will likely incorporate the copper weights, dielectric continuous, as well as thickness of core and pre-preg layers in multi-layer boards. Unless your circuit is incredibly uncomplicated I suggest that a four layer board is utilised this guarantees a continuous ground plane. When using a double sided board it's really difficult to ensure that the ground plane is un-broken. Another advantage of a 4 layer board is that the dimensions of your micro-strip for a 50 or 75 ohm style are more manageable. Use a micro-strip calculator to determine the essential track width to the design impedance and ensure that it is actually inside the manufactures capabilities, if not you could should examine the layer-stack with all the producer and select a non-standard make. A further stage to note is the fact that in my expertise attempting to sustain separate ground nets for distinct signal area's usually triggers troubles rather then any advantage and it is largely a throwback to the days before multilayer boards, just one reduced impedance ground plane is definitely the safest route.
It can be very acceptable to implement FR4 for boards up-to two.4GHz unless the highest level of overall performance is required. In selected circumstances it is worth specifying the board as managed impedance to provide constant RF efficiency.
Obtaining determined the track and board geometries the following step should be to tackle the component placement. Assure that the RF components are laid out this kind of that all of the RF tracks can be stored to the leading surface with minimum length and changes of path. Start out with low signal level areas at the antenna or RF input and function backwards in the direction of the baseband or digital location. Maintain digital and energy provide areas away from the analogue RF circuitry and keep all of the RF elements on a single side of your board.
Exactly where your RF tracks cannot be run within a straight line, use mitered bends if your CAD program supports them, in no way use suitable angled bends on RF signal lines. If mitered bends aren't supported use a series of 45 degree bends or arcs, this minimizes impedance mismatches which would boost losses and spurious emissions.
On RF layouts it's common to supply a ground flood about the major layer and to "stitch" this to the ground plane through the use of various via's. In the event you intend to do this, guarantee that the copper is stored a suitable distance from the RF tracks and elements otherwise the impedance might be lowered and induce more harm than good. The by means of spacing could be 5-10mm apart there exists extremely small advantage in stitching via's getting closer than 5mm apart.
Tracks to ground from RF elements needs to be kept as brief as is possible and use 2 or three via's in parallel via's to lessen the impedance.
沒有留言:
張貼留言