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AN-1182
APPLICATION NOTE
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Understanding and Optimizing the AFC Loop on the ADF7021 for Minimum Preamble
by Michael Dalton
Rev. 0 | Page 1 of 8
ACRONYMS AND ABBREVIATIONS
The following acronyms and abbreviations are used in this
application note:
AFC—Automatic Frequency Control
CDR—Clock and Data Recovery
DPL—Data Packet Length
LO—Local Oscillator
MI—Modulation Index
PER—Packet Error Rate
PI—Proportional Integral
RLL—Run Length Limit
Rx—Receive
SWD—Synch Word
Tx—Transmit
INTRODUCTION
Remote transceivers, within radio communication networks,
use their own independent clock sources. They are, thus,
susceptible to frequency errors. When a transmitter initiates
a communication link, the associated receiver needs to correct
these errors during the preamble phase of the data packet to
ensure correct demodulation. An effective design block that
performs this correction is an automatic frequency control
(AFC) loop. This application note provides information on
how AFC is implemented and optimized on the ADF7021,
ADF7021-N, and ADF7021-V.
Because latency and battery life are critical for remote appli-
cations, designers are motivated to reduce the settling time
required to correct a frequency error. The ADF7021 series
radios typically require up to 15 bytes of preamble to correct a
frequency error. There are methods to reduce this number to
4 to 6 bytes.
This application note outlines the various parameters that affect
the response of the AFC loop and presents the recommended
settings that enable fast settling time for specific use cases while
detailing the trade-offs in performance that are incurred.
