MICRF033BM Micrel Inc, MICRF033BM Datasheet - Page 8

• Manufacturer Part Number: MICRF033BM
• Manufacturer: Micrel Inc

Specifications of MICRF033BM

• Lead Free Status / Rohs Status: Not Compliant

October 1999
MICRF003
Functional Description
Please refer to “MICRF003 Block Diagram”. Identified in
the block diagram are the four principal functional blocks of
the IC, namely (1) UHF Downconverter, (2) OOK
Demodulator, (3) Reference and Control, and (4) Wakeup.
Also shown in the figure are two capacitors (CTH, CAGC)
and one timing component (CR), usually a ceramic
resonator.
capacitor, these are all the external components needed
with the MICRF003 to construct a complete UHF receiver.
Four control inputs are shown in the block diagram, SEL0,
SEL1, SWEN, and SHUT. Through these logic inputs the
user can control the operating mode and selectable features
of the IC. These inputs are CMOS compatible, and are
pulled-up on the IC.
Input SWEN selects the operating mode of the IC (FIXED
mode or SWP mode). When low, the IC is in FIXED mode,
and functions as a conventional superheterodyne receiver.
When SWEN is high, the IC is in SWP mode. In this mode,
while the topology is still superheterodyne, the local
oscillator (LO) is deterministically swept over a range of
frequencies at rates greater than the data rate.
coupled with a peak-detecting demodulator, this technique
effectively increases the RF bandwidth of the MICRF003, so
the device can operate in applications where significant
Transmitter/Receiver frequency misalignment may exist.
[Note:
bandwidth, so noise performance is not impacted relative to
FIXED mode. In other words, the IF bandwidth is the same
(1.18MHz) whether the device is in FIXED or SWP mode.]
Due to limitations imposed by the LO sweeping process, the
upper limit on data rate in SWP mode is approximately
5kbps. Data rates beyond 20kbps are possible in FIXED
mode however.
Examples of SWP mode operation include applications
which
transmit frequency may vary up to
tolerance, aging, and temperature. In this (patent-pending)
mode, the LO frequency is varied in a prescribed fashion
which results in downconversion of all signals in a band
approximately 1.5% around the transmit frequency. So the
Transmitter may drift up to
retune the Receiver, and without impacting system
performance.
currently available crystal-based superheterodyne receivers,
which can operate only with SAW or crystal based
transmitters.
[Note: In SWP mode only, a range penalty will occur in
installations where there exists a competing signal of
sufficient strength in this small frequency band of 1.5%
around the transmit frequency. This results from the fact
that sweeping the LO indiscriminantly “sweeps” all signals
within the sweep range down into the IF band. This same
penalty also exists with super-regenerative type receivers,
as their RF bandwidth is also generally 1.5%.
utilize
The swept LO technique does not affect the IF
With the exception of a supply decoupling
low-cost LC-based transmitters, whose
Such performance is not achieved with
0.5% without the need to
0.5% over initial
So any
When
QwikRadio
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application for a super-regenerative receiver is also an
application for the MICRF003 in SWP mode.]
For applications where the transmit frequency is accurately
set for other reasons (e.g., applications where a SAW
transmitter is used for its mechanical stability), the user
may choose to configure the MICRF003 as a standard
superheterodyne receiver (FIXED mode), mitigating the
aforementioned problem of a competing close-in signal.
This can be accomplished by tying SWEN to ground. Doing
so forces the on-chip LO frequency to a fixed value. In
FIXED mode, the ceramic resonator would be replaced with
a crystal.
operated in SWP mode, using a ceramic resonator , with
either LC or CRYSTAL/SAW based transmitters, without
any significant range difference.
The inputs SEL0 and SEL1 control the Demodulator filter
bandwidth in four binary steps (750Hz-6000Hz in SWP,
2800Hz-22400Hz in FIXED mode), and the user must select
the bandwidth appropriate to his needs.
Rolloff response of the IF Filter is 5
demodulator data filter exhibits a 2
Multiplication factor between the REFOSC frequency Ft and
the internal Local Oscillator (LO) is 129X for FIXED mode,
and 128.5X for SWP mode (i.e., for Ft = 6.75MHz in FIXED
mode, LO frequency = 6.75MHz * 129 = 870.75MHz).
Slicing Level and the CTH Capacitor
Extraction of the DC value of the demodulated signal for
purposes of logic-level data slicing is accomplished by
external capacitor CTH and the on-chip switched-cap
“resistor” RSC, indicated in the block diagram.
effective resistance of RSC is 90kohms. The value of
capacitor CTH is easily calculated, once the slicing level
time-constant is chosen. Slicing Level time constant values
vary somewhat with decoder type, data pattern, and data
rate, but typical values range 5-50msec. Optimization of
the CTH value is required to maximize range, as discussed
in “Application Note TBD”.
During quiet periods (i.e., no signal transmissions) the Data
Output (DO pin) transitions randomly based on noise. This
may present problems for some decoders.
common solution is to introduce a small offset (“Squelch”)
on the CTH pin so that noise does not trigger the internal
comparator.
introduced by connecting a several-Megohm resistor from
the CTH pin to either VSS or VDD, depending on the
desired offset polarity. Since the MICRF003 is an AGC’d
receiver, noise at the internal comparator input is always
the same, set by the AGC.
requirement does not change as the local “ether” noise
changes from installation to installation.
introducing squelch will reduce range modestly, so only
introduce an amount sufficient to “quiet” the output.
AGC Function and the CAGC Capacitor
tm
Generally, however,
Usually 20-30mV is sufficient, and may be
So the squelch offset
the MICRF003 can be
nd
th
order, while the
order response.
MICRF003
Micrel
Note that
The most
The