Budgeting Harmonics for ZigBee Front End Modules By Stephane Wloczysiak, Skyworks Solutions, Inc.

Keywords ZigBee® Systems 2.4 GHz IEEE Std 802.15.4TM-2003 Standard Front-end Module Regulatory Standard Emission Requirements Harmonics Spurious Envelope Detector

Introduction The growth of low power, cost effective wireless systems is driving more applications to use ZigBee protocol. While for some of them, the signal needs to propagate over a short range, when covering a large building or operating outdoor over a wide range for example, the system may benefit from transmitting more power. Actually [1] shows that a ZigBee radio system powered by a 20dBm power amplifier (PA) significantly increases its range compared to a low power 0dBm by 400% from 133 to 543 meters. However, adding a transmit PA may generate higher spurious, in particular -- the harmonic spurs. And additional filtering is required to satisfy radiated emission requirement of the different regulatory standards listed in Table 1. This document details how to specify harmonics for a ZigBee FEM. It reviews the requirements from the different regulatory standards, analyzes through simulation harmonics content of offset quadrature phase-shift keying (OQPSK) spread spectrum modulation and evaluates the effects of the measurement bandwidth and detector on the harmonics level of both sine and ZigBee waveforms. Finally, measurement data is provided to illustrate the simulations results.

Radiated Emission Regulatory Requirements In the United States, radiated emission requirements are provided under Federal Communications Commission regulation FCC CFR47, part 15; in Europe, ETSI EN 300 440-1/EN 300 328; and ARIB STD-T66 in Japan. Annex F of IEEE Std 802.15.4 [2] summarizes the requirements that are also listed in Table 1 for 2.4 GHz operation. Note that spurious requirements in Table 1 are relevant for the harmonic frequencies. Beside the absolute dBm limit, test conditions that include the measurement bandwidth and detector type also differ between the different standards, which may relax the actual requirement.

FCC CFR47 

Maximum Power  Peak Power  density  Narrow band  Spurious  Emission  Wide band  Emission 

ETSI EN 300 440-1/EN 300 328 

ARIB STD-T66 

Detector 

Limit 

Detector 

Limit 

Detector 

Limit 

Average 

30dBm 

RMS/Peak  (compensated  for duty cycle) 

20/23dBm 

Peak 

10mW/MHz  (10dBm/MHz) 

Average 

8dBm/3kHz 

Peak 

10dBm/MHz 

‐ 

‐ 

Average 

‐20dBc/100kHz 

Peak