In the past five years, Connected and Machine-to-Machine (M2M) Devices
have become increasingly smaller; many use embedded antennas and may
include requirements for GPS, Wi-Fi, NFC, and/or 915Mhz.
to this, they incorporate more cellular bands than before for 3G and 4G,
and customers are now looking for global coverage too. Network
congestion also adds to the problem as we pump more data onto 3G and 4G
pipes. The end result is that for devices that are as small as a cell
phone, noise and emissions have become a significant problem.
increased RF design complexity makes it almost impossible to fully
contain noise and emissions that impact transmission and reception.
Inband noise occurs when a device has emissions or harmonics of
emissions present at the operating cellular frequencies. This noise can
affect initial cellular reception or be reradiated by the cellular
module. If the antenna efficiency and radiated power of the system is
very high, it makes the problem worse.
What to do about it?
key to solving this engineering challenge is to eliminate or suppress
the noise that is causing performance compromises and most likely
certification challenges. The first thing to do is to identify the
noise source and then act to solve the problem by stopping the noise,
filtering it or at least mitigating its affects on the system. Patching
things up a little or using a less efficient antenna is not advised - it
will only end up in a poor user experience in the field. Quite often
the noise doesn’t come from one single source; it is a combination of
different factors. Ideally, you should look at the RF design at the
beginning of the product design process to help minimize these emission
effects and to keep them away from the antennas. Best practice RF design
only comes with experience, that is, learning the hard way.
Six Steps to Eliminating Noisy Devices
Select the right antenna: The first step is to team up with a wireless
product designer to select and integrate the right antenna component
selection. Size, position and mounting mechanisms are vital
considerations. Avoid large components on the board itself, which are
normally older types, and follow the component layout guidelines
closely. • Choose connectors carefully: Eliminate test points (at
the end), connectors and wires. If this is not possible minimize them
by using the latest powerful PCB design software to filter and bypass
every integrated circuit. • Use the right PCB: It is important for
the PCB stack up configuration to be designed to contain emissions and
to be optimized for RF. A four-layer board may be more expensive, but
it more than pays for itself in performance when you compare it to a
two-layer board. • Consider Traces: The routing of all power and
signal traces and their thicknesses are critical for good RF
performance. The distances between these traces and their impedances are
also vital in order to achieve the best device performance • Be
aware of the ground plane: The size of the ground plane is important
for antenna performance. For overall RF performance it is important to
completely fill in the ground plane. This means ensuring that all unused
areas of the PCB are filled with copper and not ground free. The ground
plane should be one consistent, coherent and connected “pour” so you
can see copper on all unused areas of the PCB, even between components. •
Review Shielding: Implement shielding where necessary. In some cases,
it may even be required to add shielding cans over active circuitry or
potential sources of emissions like clocks or processors etc.
A Quiet Life
products can look similar to the eye, but one device could be noisy and
the other one not, even though they are using the same components.
It’s all about the way the system is laid out and how certain components
interact with each other. Partnering with an expert who has the right
equipment, expertise and experience can help you design your product
better and quicker. The end goal is to design products that are
optimized from an RF perspective so you can enhance sensitivity and
minimize the noise effects in your device.
O’Shea is co-founder and joint managing director of Taoglas Group
Holdings. Taoglas has a Noise Control Division (NCD) in San Diego,
California, where the company’s on site engineering team is dedicated to
helping M2M manufacturers design the best devices in the market and
pass certification and approval processes easily and cost effectively.
I guess that is why we are seeing more addition of NS emission requirements in 3GPPs. and adding more and more bands on a single SKU is complicating things further and needs to be address propely. Also, sometime I see people using power and RF traces on same inner layer that are not recommended and adds more complications.
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