Application Note 22
Micrel
Application Note 22
MICRF001 Theory of Operation
by Tom Yestrebsky
About This Application Note
This application note is intended to provide detailed applica-
tion information for the MICRF001 QwikRadio鈩?Receiver IC.
All aspects of device application, including operating modes,
frequency selection, data rate selection, and external compo-
nent selection, will be discussed in-depth. Important aspects
of system design, and design trade-offs, are also discussed.
Micrel appreciates that prospective customers reflect a broad
range of expertise and experience. Some readers will already
be well-versed in developing and using remote-control wire-
less data links, while others may need further guidance. This
is further complicated by the fact that governmental regula-
tion of systems employing devices like the MICRF001 vary
from country to country.
This application note contains additional information for pro-
spective users who need further guidance. A glossary is
provided at the end of this application note. Also provided is
a subject-matter bibliography, which identifies related appli-
cation notes, and other material which may be useful, de-
pending on background and interest.
鈥?Complete compatibility with both LC and SAW
transmitters
鈥?Programmable, fully integrated (demodulator)
baseband filtering
鈥?Virtual elimination of LO reradiation
鈥?Low-cost, high-reliability CMOS technology
鈥?Lowest parts count in the industry
Applying the MICRF001
The MICRF001, because of its high level of functional inte-
gration, requires only one ceramic resonator and two capaci-
tors to form a complete UHF OOK receiver for wireless
applications. Neither of the capacitors are high-precision
components, and the ceramic resonator need only exhibit a
modest
鹵0.5%
initial accuracy. Range performance with a
quarter-wave antenna is typically 100 meters open-field. To
complete the design process, the user need only perform
three simple calculations:
鈥?Compute the frequency of the ceramic resonator
鈥?Determine the slicing-level time constant
and compute C
TH
鈥?Determine the AGC time constant and compute
C
AGC
MICRF001 UHF Receiver Overview
The MICRF001 was designed as a cost-competitive solution
to existing superregenerative receivers and superhetero-
dyne receivers, for remote-control type wireless data links.
Further, due to topological improvements and higher levels of
integration, this IC is more easily applied than any before it,
and the user does not need to be an 鈥淩F expert.鈥?/div>
The MICRF001 is a complete superheterodyne OOK re-
ceiver IC, intended for use in the UHF frequency band from
300MHz to 440MHz. The IC incorporates complete UHF
down conversion and data demodulation functions on the
same IC and provides data output (logic levels) compatible
with a wide variety of data decoder ICs. Micrel鈥檚 proprietary
enhancements to the superheterodyne topology lower manu-
facturing costs and speed time-to-market.
The MICRF001 is data format independent and may be easily
incorporated into both existing and new applications. Further,
the MICRF001 is completely compatible with either SAW-
based or LC transmitters, without any transmitter modifica-
tions whatsoever. Range performance of the device is typi-
cally 100 meters, depending on data format, data rate, and
antenna type.
Patent-pending design techniques provide features un-
matched by any previous solution, namely:
鈥?Complete elimination of expensive and bulky SAW
resonators and coils
鈥?Automatic receive frequency tuning and alignment
anywhere in 300MHz to 440MHz band
Superregenerative vs. Superheterodyne
Superregenerative (SR) Receivers
In most radio applications, the receiver is selectivity-limited.
In other words, the minimum signal recoverable by the
receiver is limited not by the thermal noise of the receiver
(which sets the receiver 鈥渟ensitivity鈥?, but other 鈥渘oise鈥?lo-
cated in the 鈥渆ther,鈥?for example from other transmitters, like
FM radio stations. Until the advent of the MICRF001, the
simplest and most cost-effective UHF radio receiver for
wireless remote-control applications was the SR receiver
1,2
.
SR receivers have been around for many decades, have an
RF bandwidth of several MHz, and demonstrate a typical
range of about 100 meters. SR receivers are basically
homodyne (direct-to-baseband) receivers, elegant in their
simplicity, but analytically difficult to understand due to their
inherent nonlinearity. Development and optimization of these
receivers is generally an empirical process.
SR receivers exhibit a number of drawbacks, limiting their
application and ease-of-use, namely:
鈥?Reradiate RF noise (called 鈥渞egen noise鈥?, for which
regulatory limits usually exist
3,4
鈥?Require manual frequency tuning
鈥?鈥淩egen noise鈥?crosstalk limits how closely SR
receivers can be collocated
QwikRadio is a trademark of Micrel, Inc. The QwikRadio ICs were developed under a partnership agreement with AIT of Orlando, Florida
Micrel, Inc. 鈥?1849 Fortune Drive 鈥?San Jose, CA 95131 鈥?USA 鈥?tel + 1 (408) 944-0800 鈥?fax + 1 (408) 944-0970 鈥?http://www.micrel.com
October 1999
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