Written by Chris Pinter
January 25, 2010
Every engineer should know something about radios. These 10 items are critical to understand before you consider your next Wi-Fi, Bluetooth or Wireless design. If you need help with wireless product development consider these items as a starting point to success.
1. Requirements make your project easy.
Believe it or not, if you do not know what you are developing at the start you may never reach your intended result. At the end of a wireless development project your product might just end up being whatever you were able to accomplish with the resources you have at hand and not what you really wanted.
2. Design for certification then performance.
Performance is what your customer will want but the certification body that controls the regulation will tell you what you can sell. Often times, it’s the certification body that will control what your Wi-Fi or Bluetooth product performance requirements will be. More often than not when a wireless product is faced with a certification failure it is the performance that must be reduced in order for the product to pass certification.
3. The wireless channel is a hostile environment.
Unlike wired transmission lines the radio waves that propagate through space can experience interference and attenuation from obstacles and other radio waves propagating through the same space. You need to understand the application needs and the nature of radio propagation before you start your design. Do some research on all of radio technology used in your spectrum band of choice and the environment the radio will be used in. Wireless Engineering requires a lot of forethought before the design can be started.
4. Radios are not like digital and analog circuits.
Radio frequency design is kind of like black magic only because radio developers do not think about the printed circuit board (PCB) as part of the circuit. Remember a radio wave has a phase and amplitude. It is easier to look at the traces on the PCB more like a suggested route for the propagating wave to follow rather than a confined copper trace containing a high frequency digital signal.
5. Any noise on a power line will kill radio sensitivity.
The radio receiver is the most sensitive circuit in any radio. If you can see noise on a power line using an oscilloscope, so can the radio receiver. Using filter caps and inductors…not ferrite beads… to filter the noise at the radio IC location is the best way to reduce the ripple on the power supply line.
6. Every trace has a capacitance and inductance component.
The length and width of each trace must be considered. Even the return ground path is part of the circuit. Consider the signal on the ground path as it moves throughout your circuit back to the power source. Make sure to use a ground plan rather than a mesh network or lose grouping of ground traces.
7. Microwave design is all about impedance and phase.
The smith chart is your friend. The impedance of a radio frequency transmission line must be the same…or very close to the impedance of the source and load you are attempting to communicate between. If you do not you will experience reflection and you will not get maximum power transfer to the load.
8. Loss tolerance creates poor performance.
The choice of capacitors and inductors are critical in helping you with impedance matching. Often times even a very high Q inductor is not good enough at 5 GHz to match the transmission line. Consider using microstrip technology to overcome tolerance issues. If you have a problem with this Pinter Electronics Consultants can help.
9. Gauss’s law of magnetism is one of Maxwell’s equations.
Cellular phone signals such as a GSM signal can plague a radio design and do not always remain confined within controlled area of the circuit. Sometime GSM noise appear on other parts of the product. An audio thumping hum can appear on speakers and low frequency circuits. Shielding and filtering only works so much to suppress the electrical field. Consider using ferrite material and ferrite beads to suppress the magnetic field in order to reduce the unwanted radiated energy.
10. Radio design is expensive to the inexperienced.
Experience counts for a lot. Many developers’ first look at a radio project as a simple exercise of reading the datasheet and application notes, plopping down the parts onto your favorite PCB layout tool and creating a prototype, which you then attempt to debug for weeks at a time if necessary. Then repeat this process several times until you are so frustrated you give up or you end up spending a lot to time and money in debug.
Don’t waste your time in the learning curve and the investment of the several 100 of thousands of dollars in engineering salaries and test equipment required to make a radio project successful. You need a specialist…Get the Best. Call Pinter Electronics Consultants when you want to start your next radio development project.
John D. Kraus, Daniel A. Fleisch, “Electromagnetics with Application” WCB McGraw-Hill Publication, NewYork, NY, ISBN 0-07-289969-7
Ryan Winfield Woodings, Mark Gerrior of Cyprus Semiconductors, “Avoiding Interference in the 2.45 GHz ISM Band”, wwwmwee.com, February 16, 2005, Microwave Journal