NEO-D9C - Integration manual
emits from unshielded I/O lines. Receiver performance may be degraded when this noise is coupled
into the antenna.
EMI protection measures are particularly useful when RF emitting devices are placed next to the
receiver and/or to minimize the risk of EMI degradation due to self-jamming. An adequate layout
with a robust grounding concept is essential in order to protect against EMI.
Intended Use: In order to mitigate any performance degradation of a radio equipment under
EMC disturbance, system integration shall adopt appropriate EMC design practice and not
contain cables over three meters on signal and supply ports.
4.6.1 General notes on interference issues
Received signal power at the antenna is very low. At the nominal received signal strength (-128
dBm) it is below the thermal noise floor of -111 dBm. Due to this fact, a receiver is susceptible to
interference from nearby RF sources of any kind. Two cases can be distinguished:
• Out-of-band interference: Typically any kind of wireless communications system (e.g. LTE,
GSM, CDMA, 3G, WLAN, Bluetooth, etc.) may emit its specified maximum transmit power in
close proximity to the receiving antenna, especially if such a system is integrated with the
receiver. Even at reasonable antenna selectivity, destructive power levels may reach the RF
input of the receiver. Also, larger signal interferers may generate intermodulation products
inside the receiver front-end that fall into the band and contribute to in-band interference.
• In-band interference: Although the band is kept free from intentional RF signal sources by
radio-communications standards, many devices emit RF power into the band at levels much
higher than the signal itself. One reason is that the frequency band above 1 GHz is not well
regulated with regards to EMI, and even if permitted, signal levels are much higher than signal
power. Notably, all types of digital equipment, such as PCs, digital cameras, LCD screens,
etc. tend to emit a broad frequency spectrum up to several GHz of frequency. Also wireless
transmitters may generate spurious emissions that fall into band.
As an example, GSM uses power levels of up to 2 W (+33 dBm). The absolute maximum power input
at the RF input of the receiver can be +15 dBm. The GSM specification allows spurious emissions
for GSM transmitters of up to +36 dBm, while the signal is less than -128 dBm. By simply comparing
these numbers it is obvious that interference issues must be seriously considered in any design of
a receiver. Different design goals may be achieved through different implementations:
• The primary focus is to prevent damaging the receiver from large input signals. Here the
performance under interference conditions is not important and suppression of the signal
is permitted. It is sufficient to just observe the maximum RF power ratings of all of the
components in the RF input path.
• performance must be guaranteed even under interference conditions. In such a case, not only
the maximum power ratings of the components in the receiver RF path must be observed.
Further, non-linear effects like gain compression, NF degradation (desensitization) and
intermodulation must be analyzed.
Pulsed interference with a low-duty cycle such as GSM may be destructive due to the high
peak power levels.
4.6.2 In-band interference mitigation
With in-band interference, the signal frequency is very close to the frequency. Such interference
signals are typically caused by harmonics from displays, micro-controller operation, bus systems,
etc. Measures against in-band interference include:
• Maintaining a good grounding concept in the design
• Shielding
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4 Design
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