MICRF002/RF022
300-440MHz QwikRadio
®
ASK Receiver
QwikRadio is a registered trademark of Micrel, Inc. The QwikRadio ICs were developed under a partnership agreement with AIT of Orlando, FL.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
July 2008
M9999-070808
General Description
The MICRF002 is a single chip ASK/OOK (ON-OFF
Keyed) RF receiver IC. This device is a true “antenna-in to
data-out” monolithic device. All RF and IF tuning is
accomplished automatically within the IC which eliminates
manual tuning and reduces production costs. The result is
a highly reliable yet low cost solution.
The MICRF002 is a fully featured part in 16-pin packaging,
the MICRF022 is the same part packaged in 8-pin
packaging with a reduced feature set (see “Ordering
Information” for more information).
The MICRF002 is an enhanced version of the MICRF001
and MICRF011. The MICRF002 provides two additional
functions over the MICRF001/011, (1) a Shutdown pin,
which may be used to turn the device off for duty-cycled
operation, and (2) a “Wake-up” output, which provides an
output flag indicating when an RF signal is present. These
features make the MICRF002 ideal for low and ultra-low
power applications, such as RKE and remote controls.
All IF filtering and post-detection (demodulator) data
filtering is provided within the MICRF002, so no external
filters are necessary. One of four demodulator filter
bandwidths may be selected externally by the user.
The MICRF002 offer two modes of operation; fixed-mode
(FIX) and sweep-mode (SWP). In fixed-mode the
MICRF002 functions as a conventional superhet receiver.
In sweep-mode the MICRF002 employs a patented
sweeping function to sweep a wider RF spectrum. Fixed-
mode provides better selectivity and sensitivity
performance and sweep-mode enables the MICRF002 to
be used with low cost, imprecise transmitters.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
QwikRadio
®
Features
• 300MHz to 440MHz frequency range
• Data-rate up to 10kbps (fixed-mode)
• Low Power Consumption
• 2.2mA fully operational (315MHz)
• 0.9µA in shutdown
• 220µA in polled operation (10:1 duty-cycle)
• Wake-up output flag to enable decoders and
microprocessors
• Very low RF re-radiation at the antenna
• Highly integrated with extremely low external part count
Applications
• Automotive remote keyless entry (RKE)
• Remote controls
• Remote fan and light control
• Garage door and gate openers
_________________________________________________________________________________________________________
Ordering Information
Part Number Demodulator
Bandwidth Operating Mode Shutdown WAKEB
Output Flag Package Lead Finish
MICRF002YM User Programmable Fixed or Sweep Yes Yes 16-Pin SOIC Pb-Free
MICRF022YM-SW48 5000Hz Sweep No Yes 8-Pin SOIC Pb-Free
MICRF022YM-FS12 1250Hz Fixed Yes No 8-Pin SOIC Pb-Free
MICRF022YM-FS24 2500Hz Fixed Yes No 8-Pin SOIC Pb-Free
MICRF022YM-FS48 5000Hz Fixed Yes No 8-Pin SOIC Pb-Free
Micrel, Inc. MICRF002/RF022
July 2008
2 M9999-070808
Typical Application
SEL0SEL0 SWEN
VSSRF REFOSC
VSSRF SEL1
ANT CAGC
VDDRF WAKEB
VDDBB SHUT
CTH DO
NC VSSBB
0.047µF
4.8970MHz
Data
Output
MICRF002
4.7µF
+5V
15nH
10pF
68nH
1/4 Wave Monopole
315MHz 800bps On-Off Keyed Receiver
Pin Configur ation
1SEL0
VSSRF
VSSRF
ANT
VDDRF
VDDBB
CTH
NC
16 SWEN
REFOSC
SEL1
CAGC
WAKEB
SHUT
DO
VSSBB
15
14
13
12
11
10
9
2
3
4
5
6
7
8
1VSSRF
ANT
VDDRF
CTH
8 REFOSC
CAGC
SHUT/WAKEB
DO
7
6
5
2
3
4
16-Pin SOIC (M) 8-Pin SOIC (M)
8-Pin Options
The standard 16-pin package allows complete control of
all configurable features. Some reduced function 8-pin
versions are also available, see “Ordering Information”
on page 1.
For high-volume applications additional customized 8-pin
devices can be produced. SWEN, SEL0 and SEL1 pins
are internally bonded to reduce the pin count; pin 6 may
be configured as either SHUT or WAKEB
Demodulator Bandwidth
SEL0 SEL1 Sweep-Mode Fixed-Mode
1 1 5000Hz 10000Hz
0 1 2500Hz 5000Hz
1 0 1250Hz 2500Hz
0 0 625Hz 1250Hz
Table 1. Nominal Demodulator Filter Bandwidth vs.
SEL0, SEL1 and Operating Mode
Micrel, Inc. MICRF002/RF022
July 2008
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M9999-070808
Pin Description
Pin Number
SOIC-16 Pin Number
SOIC-8 Pin Name Pin Name
1 – SEL0
Bandwidth Selection Bit 0 (Digital Input): Used in conjunction with SEL1 to set
the desired demodulator filter bandwidth. See Table 1. Internally pulled-up to
VDDRF.
2, 3 1 VSSRF RF Power Supply: Ground return to the RF section power supply.
4 2 ANT
Antenna (Analog Input): For optimal performance the ANT pin should be
impedance matched to the antenna. See “Applications Information” for
information on input impedance and matching techniques.
5 3 VDDRF RF Power Supply: Positive supply input for the RF section of the IC.
6 – VDDBB
Base-Band Power Supply: Positive supply input for the baseband section
(digital section) of the IC.
7 4 CTH
Data Slicing Threshold Capacitor (Analog I/O): Capacitor connected to this
pin extracts the dc average value from the demodulated waveform which
becomes the reference for the internal data slicing comparator.
8 – NC Not internally connected
9 – VSSBB
Base-Band Power Supply: Ground return to the baseband section power
supply.
10 5 DO Data Output (Digital Output)
11 6 SHUT
Shutdown (Digital Input): Shutdown-mode logic-level control input. Pull low to
enable the receiver. Internally pulled-up to VDDRF.
12 – WAKEB
Wakeup (Digital Output): Active-low output that indicates detection of an
incoming RF signal.
13 7 CAGC
Automatic Gain Control (Analog I/O): Connect an external capacitor to set the
attack/decay rate of the on-chip automatic gain control.
14 – SEL1
Bandwidth Selection Bit 1 (Digital Input): Used in conjunction with SEL0 to set
the desired demodulator filter bandwidth. See Table 1. Internally pulled-up to
VDDRF.
15 8 REFOSC Reference Oscillator: Timing reference, sets the RF receive frequency.
16 – SWEN
Sweep-Mode Enable (Digital Input): Sweep- or Fixed-mode operation control
input. SWEN high= sweep mode; SWEN low = conventional superheterodyne
receiver. Internally pulled-up to VDDRF.
Micrel, Inc. MICRF002/RF022
July 2008
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Absolute Maximum Ratings(1)
Supply Voltage (V
DDRF
, V
DDBB
)........................................+7V
Input/Output Voltage (V
I/O
). ....................V
SS
–0.3 to V
DD
+0.3
Junction Temperature (T
J
) ....................................... +150°C
Storage Temperature (T
s
) ........................... –65°C to 150°C
Lead Temperature (soldering, 10 sec.)...................... 260°C
ESD Rating
(3)
Operating Ratings(2)
Supply Voltage (V
DDRF
, V
DDBB
).................... +4.75V to +5.5V
RF Frequency Range.............................. 300MHz to 440Hz
Data Duty-Cycle ................................................20% to 80%
Reference Oscillator Input Range.............. 0.1V
PP
to 1.5V
PP
Ambient Temperature (T
A
) ..........................–40°C to +85°C
Electrical Characteristics(4)
V
DDRF
= V
DDBB
= V
DD
where +4.75V ≤ V
DD
≤ 5.5V, V
SS
= 0V; C
AGC
= 4.7µF, C
TH
= 100nF; SEL0 = SEL1 = V
SS
; fixed mode
(SWEN = V
SS
); f
REFOSC
= 4.8970MHz (equivalent to f
RF
= 315MHz); data-rate = 1kbps (Manchester encoded). T
A
= 25°C,
bold values indicate –40°C ≤ T
A
≤ +85°C; current flow into device pins is positive; unless noted.
Symbol Parameter Condition Min Typ Max Units
continuous operation, f
RF
= 315MHz 2.2 3.2 mA I
OP
Operating Current
polled with 10:1 duty cycle, f
RF
= 315MHz 220 µA
continuous operation, f
RF
= 433.92MHz 3.5 mA
polled with 10:1 duty cycle, f
RF
= 433.92MHz 350 µA
I
STBY
Standby Current V
SHUT
= V
DD
0.9 µA
RF Section, IF Section
Receiver Sensitivity (Note 4) f
RF
= 315MHz –97 dBm
f
RF
= 433.92MHz –95 dBm
f
IF
IF Center Frequency Note 6 0.86 MHz
f
BW
IF Bandwidth Note 6 0.43 MHz
Maximum Receiver Input R
SC
= 50Ω –20 dBm
Spurious Reverse Isolation ANT pin, R
SC
= 50Ω, Note 5 30 µV
RMS
AGC Attack to Decay Ratio t
ATTACK
÷ t
DECAY
0.1
AGC Leakage Current T
A
= +85°C ±100 nA
Reference Oscillator
Z
REFOSC
Reference Oscillator Input
Impedance
Note 8 290 kΩ
Reference Oscillator Source
Current
5.2 µA
Demodulator
Z
CTH
CTH Source Impedance Note 7 145 kΩ
I
ZCTH(leak)
CTH Leakage Current T
A
= +85°C ±100 nA
Demodulator Filter Bandwidth
Sweep Mode
(SWEN = VDD or OPEN)
Note 6
V
SEL0
= V
DD
. V
SEL1
= V
DD
V
SEL0
= V
SS
. V
SEL1
= V
DD
V
SEL0
= V
DD
. V
SEL1
= V
SS
V
SEL0
= V
SS
. V
SEL1
= V
SS
4000
2000
1000
500
Hz
Hz
Hz
Hz
Demodulator Filter Bandwidth
Fixed Mode
(SWEN = VSS)
Note 6
V
SEL0
= V
DD
. V
SEL1
= V
DD
V
SEL0
= V
SS
. V
SEL1
= V
DD
V
SEL0
= V
DD
. V
SEL1
= V
SS
V
SEL0
= V
SS
. V
SEL1
= V
SS
8000
4000
2000
1000
Hz
Hz
Hz
Hz
Micrel, Inc. MICRF002/RF022
July 2008
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M9999-070808
Symbol Parameter Condition Min Typ Max Units
Digital/Control Section
V
IN(high)
Input-High Voltage SEL0, SEL1, SWEN 0.8 V
DD
V
IN(low)
Input-Low Voltage SEL0, SEL1, SWEN 0.2 V
DD
I
OUT
Output Current DO, WAKEB pins, push-pull 10 µA
V
OUT(high)
Output High Voltage DO, WAKEB pins, I
OUT
= –1µA 0.9 V
DD
V
OUT(low)
Output Low Voltage DO, WAKEB pins, I
OUT
= +1µA
0.1 V
DD
t
R
, t
F
Output Rise and Fall Times DO, WAKEB pins, C
LOAD
= 15pF 10 µs
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive, use appropriate ESD precautions. Meets class 1 ESD test requirements, (human body model HBM), in accordance with
MIL-STD-883C, method 3015. Do not operate or store near strong electrostatic fields.
4. Sensitivity is defined as the average signal level measured at the input necessary to achieve 10-2 BER (bit error rate). The RF input is assumed to be
matched to 50Ω.
5. Spurious reverse isolation represents the spurious components which appear on the RF input pin (ANT) measured into 50Ω with an input RF
matching network.
6. Parameter scales linearly with reference oscillator frequency f
T
. For any reference oscillator frequency other than 4.8970MHz, compute new
parameter value as the ratio:.
4.8970MHz) at value (parameter
4.8970MHz
MHz
REFOSC
f
×
7. Parameter scales inversely with reference oscillator frequency f
T
. For any reference oscillator frequency other than 4.8970MHz, compute new
parameter value as the ratio:
4.8970MHz) at value (parameter
MHz
REFOSC
f
4.8970MHz ×
8. Series resistance of the resonator (ceramic resonator or crystal) should be minimized to the extent possible. In cases where the resonator series
resistance is too great, the oscillator may oscillate at a diminished peak-to-peak level, or may fail to oscillate entirely. Micrel recommends that series
resistances for ceramic resonators and crystals not exceed 50Ohms and 100Ω respectively. Refer to Application Hint 35 for crystal
recommendations.
Micrel, Inc. MICRF002/RF022
July 2008
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M9999-070808
Typical Characteristics
1.5
3.0
4.5
6.0
250 300 350 400 450 500
CURRENT (mA)
FREQUENCY (MHz)
Supply Current
vs. Frequency
T
A
=25°C
V
DD
=5V
Sweep Mode,
Continuous Operation
1.5
2.0
2.5
3.0
3.5
-40 -20 0 20 40 60 80 100
CURRENT (mA)
TEMPERATURE (°C)
Supply Current
vs. Temperature
f = 315MHz
V
DD
=5V
Sweep Mode,
Continuous Operation
Micrel, Inc. MICRF002/RF022
July 2008
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M9999-070808
Functional Diagram
Peak
Detector
AGC
Control
2nd Order
Programmable
Low-Pass Filter
5th Order
Band-Pass Filter
Synthesizer
Control
Logic
R
SC
Resettable
Counter
Reference
Oscillator
Cystal
or
Ceramic
Resonator
CAGC
ANT
SEL0
VDD
VSS
SEL1
SWEN
REFOSC
430kHz
Switched-
Capacitor
Resistor
WAKEB
CTH
DO
MICRF002
RF
Amp
IF
Amp
IF
Amp Compa-
rator
WakeupReference and Control
UHF Downconverter OOK Demodulator
f
RX
f
LO
f
IF
SHUT
C
AGC
C
TH
f
T
Figure 1. MICRF002 Block Diagram
Application Information and Functional
Description
Refer to Figure 1 “MICRF002 Block Diagram”. Identified in
the block diagram are the four sections of the IC: UHF
Downconverter, OOK Demodulator, Reference and
Control, and Wakeup. Also shown in the figure are two
capacitors (CTH, CAGC) and one timing component,
usually a crystal or ceramic resonator. With the exception
of a supply decoupling capacitor, and antenna impedance
matching network, these are the only external components
needed by the MICRF002 to assemble a complete UHF
receiver.
For optimal performance is highly recommended that the
MICRF002 is impedance matched to the antenna, the
matching network will add an additional two or three
components.
Four control inputs are shown in the block diagram: SEL0,
SEL1, SWEN, and SHUT. Using these logic inputs, the
user can control the operating mode and selectable
features of the IC. These inputs are CMOS compatible, and
are internally pulled-up. IF Bandpass Filter Roll-off
response of the IF Filter is 5th order, while the demodulator
data filter exhibits a 2
nd
order response.
Design Steps
The following steps are the basic design steps for using the
MICRF002 receiver:
1. Select the operating mode (sweep or fixed)
2. Select the reference oscillator
3. Select the C
TH
capacitor
4. Select the C
AGC
capacitor
5. Select the demodulator filter bandwidth
Step 1: Selecting the Operating Mode
Fixed-Mode Operation
For applications where the transmit frequency is accurately
set (that is, applications where a SAW or crystal-based
transmitter is used) the MICRF002 may be configured as a
standard superheterodyne receiver (fixed mode). In fixed-
mode operation the RF bandwidth is narrower making the
receiver less susceptible to interfering signals. Fixed mode
is selected by connecting SWEN to ground.
Sweep-Mode Operation
When used in conjunction with low-cost L-C transmitters
the MICRF002 should be configured in sweep-mode. In
sweep-mode, while the topology is still superheterodyne,
the LO (local oscillator) is swept over a range of
frequencies at rates greater than the data rate. This
technique effectively increases the RF bandwidth of the
Micrel, Inc. MICRF002/RF022
July 2008
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M9999-070808
MICRF002, allowing the device to operate in applications
where significant transmitter-receiver frequency
misalignment may exist. The transmit frequency may vary
up to ±0.5% over initial tolerance, aging, and temperature.
In sweep-mode a band approximately 1.5% around the
nominal transmit frequency is captured. The transmitter
may drift up to ±0.5% without the need to retune the
receiver and without impacting system performance.
The swept-LO technique does not affect the IF bandwidth,
therefore noise performance is not degraded relative to
fixed-mode. The IF bandwidth is 430kHz whether the
device is operating in fixed- or sweep-mode. Due to
limitations imposed by the LO sweeping process, the upper
limit on data rate in sweep mode is approximately 5.0kbps.
Similar performance is not currently available with
crystalbased superheterodyne receivers which can operate
only with SAW- or crystal-based transmitters. In sweep-
mode, a range reduction will occur in installations where
there is a strong interferer in the swept RF band. This is
because the process indiscriminately includes all signals
within the sweep range. An MICRF002 may be used in
place of a superregenerative receiver in most applications.
Step 2: Selecting the Reference Oscillator
All timing and tuning operations on the MICRF002 are
derived from the internal Colpitts reference oscillator.
Timing and tuning is controlled through the REFOSC pin in
one of three ways:
1. Connect a ceramic resonator
2. Connect a crystal
3. Drive this pin with an external timing signal
The specific reference frequency required is related to the
system transmit frequency and to the operating mode of
the receiver as set by the SWEN pin.
Crystal or Ceramic Resonator Selection
Do not use resonators with integral capacitors since
capacitors are included in the IC, also care should be taken
to ensure low ESR capacitors are selected. Application Hint
34 and Application Hint 35 provide additional information
and recommended sources for crystals and resonators.
If operating in fixed-mode, a crystal is recommended. In
sweep-mode either a crystal or ceramic resonator may be
used. When a crystal of ceramic resonator is used the
minimum voltage is 300mV
PP
. If using an externally applied
signal it should be AC-coupled and limited to the operating
range of 0.1V
PP
to 1.5V
PP
.
Selecting Reference Oscillator Frequency f
T
(Fixed-
Mode)
As with any superheterodyne receiver, the mixing
between the internal LO (local oscillator) frequency f
LO
and
the incoming transmit frequency f
TX
ideally must equal the
IF center frequency. Equation 1 may be used to compute
the appropriate f
LO
for a given f
TX
:
(1) ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
±= 315
f
0.86ff
TX
TXLO
Frequencies f
TX
and f
LO
are in MHz. Note that two values of
f
LO
exist for any given f
TX
, distinguished as “high-side
mixing” and “low-side mixing”. High-side mixing results in
an image frequency above the frequency of interest and
low-side mixing results in a frequency below.
After choosing one of the two acceptable values of f
LO
, use
Equation 2 to compute the reference oscillator frequency f
T
:
(2)
64.5
f
f
LO
T
=
Frequency f
T
is in MHz. Connect a crystal of frequency f
T
to
REFOSC on the MICRF002. Four-decimal-place accuracy
on the frequency is generally adequate. The following table
identifies f
T
for some common transmit frequencies when
the MICRF002 is operated in fixed mode.
Transmit Frequency f
TX
Reference Oscillator
Frequency f
T
315MHz 4.8970MHz
390MHz 6.0630MHz
418MHz 6.4983MHz
433.92MHz 6.7458MHz
Table 2. Fixed-Mode Recommended Reference Oscillator
Values for Typical Transmit F requencies
(high-side mixing)
Selecting REFOSC Frequency f
T
(Sweep-Mode)
Selection of the reference oscillator frequency f
T
in sweep-
mode is much simpler than in fixed mode due to the LO
sweeping process. Also, accuracy requirements of the
frequency reference component are significantly relaxed.
In sweep-mode, f
T
is given by Equation 3:
(3) 64.25
f
f
LO
T
=
In sweep-mode a reference oscillator with frequency
accurate to two-decimal-places is generally adequate. A
crystal may be used and may be necessary in some cases
if the transmit frequency is particularly imprecise.
Transmit Frequency f
TX
Reference Oscillator
Frequency f
T
315MHz 4.88MHz
390MHz 6.05MHz
418MHz 6.48MHz
433.92MHz 6.73MHz
Table 3. Sweep-Mode Recommen ded Reference Osci llato r
Values for Typical Transmit F requencies
Micrel, Inc. MICRF002/RF022
July 2008
9 M9999-070808
Step 3: Selecting the C
TH
Capacitor
Extraction of the dc value of the demodulated signal
for purposes of logic-level data slicing is accomplished
using the external threshold capacitor C
TH
and the on-
chip switched capacitor “resistor” R
SC
, shown in the
block diagram.
Slicing level time constant values vary somewhat with
decoder type, data pattern, and data rate, but typically
values range from 5ms to 50ms. Optimization of the
value of C
TH
is required to maximize range.
Selecting Capacitor C
TH
The first step in the process is selection of a data-slicing-
level time constant. This selection is strongly dependent on
system issues including system decode response time and
data code structure (that is, existence of data preamble,
etc.). This issue is covered in more detail in Application
Note 22.
The effective resistance of R
SC
is listed in the electrical
characteristics table as 145kΩ at 315MHz, this value scales
linearly with frequency. Source impedance of the C
TH
pin at
other frequencies is given by Equation 4, where f
T
is in
MHz:
(4)
T
SC
f
4.8970
145kΩR=
τ of 5x the bit-rate is recommended. Assuming that a slicing
level time constant τ has been established, capacitor C
TH
may be computed using Equation 5:
(5)
SC
TH
R
τ
C=
A standard ±20% X7R ceramic capacitor is generally
sufficient. Refer to Application Hint 42 for C
TH
and CAGC
selection examples.
Step 4: Selecting the C
AGC
Capacitor
The signal path has AGC (automatic gain control) to
increase input dynamic range. The attack time constant of
the AGC is set externally by the value of the C
AGC
capacitor
connected to the C
AGC
pin of the device. To maximize
system range, it is important to keep the AGC control
voltage ripple low, preferably under 10mV
PP
once the
control voltage has attained its quiescent value. For this
reason capacitor values of at least 0.47µF are
recommended.
The AGC control voltage is carefully managed on-chip to
allow duty-cycle operation of the MICRF002. When the
device is placed into shutdown mode (SHUT pin pulled
high), the AGC capacitor floats to retain the voltage. When
operation is resumed, only the voltage droop due to
capacitor leakage must be replenished. A relatively low-
leakage capacitor is recommended when the devices are
used in dutycycled operation.
To further enhance duty-cycled operation, the AGC push
and pull currents are boosted for approximately 10ms
immediately after the device is taken out of shutdown. This
compensates for AGC capacitor voltage droop and reduces
the time to restore the correct AGC voltage. The current is
boosted by a factor of 45.
Selecting C
AGC
Capacitor in Continuous Mode
A C
AGC
capacitor in the range of 0.47µF to 4.7µF is typically
recommended. The value of the C
AGC
should be selected to
minimize the ripple on the AGC control voltage by using a
sufficiently large capacitor. However if the capacitor is too
large the AGC may react too slowly to incoming signals.
AGC settling time from a completely discharged (zero-volt)
state is given approximately by Equation 6:
(6) 0.441.333C∆t
AGC
−
=
where:
C
AGC
sin in µF, and ∆t is in seconds.
Selecting C
AGC
Capacitor in Duty-Cycle Mode
Voltage droop across the C
AGC
capacitor during shutdown
should be replenished as quickly as possible after the IC is
enabled. As mentioned above, the MICRF002 boosts the
push-pull current by a factor of 45 immediately after start-
up. This fixed time period is based on the reference
oscillator frequency f
T
. The time is 10.9ms for f
T
= 6.00MHz,
and varies inversely with f
T
. The value of C
AGC
capacitor
and the duration of the shutdown time period should be
selected such that the droop can be replenished within this
10ms period.
Polarity of the droop is unknown, meaning the AGC voltage
could droop up or down. Worst-case from a recovery
standpoint is downward droop, since the AGC pull-up
current is 1/10th magnitude of the pulldown current. The
downward droop is replenished according to the Equation
7:
(7) ∆t
∆V
C
I
AGC
=
where:
I = AGC pullup current for the initial 10ms (67.5µA)
C
AGC
= AGC capacitor value
∆t = droop recovery time
∆V = droop voltage
For example, if user desires ∆t = 10ms and chooses a
4.7µF C
AGC
, then the allowable droop is about 144mV.
Using the same equation with 200nA worst case pin
leakage and assuming 1µA of capacitor leakage in the
same direction, the maximum allowable ∆t (shutdown time)
is about 0.56s for droop recovery in 10ms.
The ratio of decay-to-attack time-constant is fixed at 10:1
(that is, the attack time constant is 1/10th of the decay time
constant). Generally the design value of 10:1 is adequate
Micrel, Inc. MICRF002/RF022
July 2008 10
M9999-070808
for the vast majority of applications. If adjustment is
required the constant may be varied by adding a resistor in
parallel with the C
AGC
capacitor. The value of the resistor
must be determined on a case by case basis.
Step 5: Selecting The Demod Filter Bandwidth
The inputs SEL0 and SEL1 control the demodulator filter
bandwidth in four binary steps (625Hz to 5000Hz in sweep,
1250Hz to 10000Hz in fixed-mode), see Table 3.
Bandwidth must be selected according to the application.
The demodulator bandwidth should be set according to
Equation 8:
(8)
widthpulse Shortest
0.65
bandwidth Demoulator −
=
It should be noted that the values indicated in Table 1 are
nominal values. The filter bandwidth scales linearly with
frequency so the exact value will depend on the operating
frequency. Refer to the “Electrical Characteristics” for the
exact filter bandwidth at a chosen frequency.
Demodulator Bandwidth
SEL0 SEL1 Sweep-Mode Fixed-Mode
1 1 5000Hz 10000Hz
0 1 2500Hz 5000Hz
1 0 1250Hz 2500Hz
0 0 625Hz 1250Hz
Table 1. Nominal Demodulator Filter Bandwidth vs.
SEL0, SEL1 and Operating Mode
Micrel, Inc. MICRF002/RF022
July 2008 11
M9999-070808
Additional Applications Information
In addition to the basic operation of the MICRF002 the
following enhancements can be made. In particular it is
strongly recommended that the antenna impedance is
matched to the input of the IC.
Antenna Impedance Matching
As shown in Table 4 the antenna pin input impedance is
frequency dependant. The ANT pin can be matched to 50Ω
with an L-type circuit. That is, a shunt inductor from the RF
input to ground and another in series from the RF input to
the antenna pin.
Inductor values may be different from table depending on
PCB material, PCB thickness, ground configuration, and
how long the traces are in the layout. Values shown were
characterized for a 0.031 thickness, FR4 board, solid
ground plane on bottom layer, and very short traces.
MuRata and Coilcraft wire wound 0603 or 0805 surface
mount inductors were tested, however any wire wound
inductor with high SRF (self resonance frequency) should
do the job.
Shutdown Function
Duty-cycled operation of the MICRF002 (often referred to
as polling) is achieved by turning the MICRF002 on and off
via the SHUT pin. The shutdown function is controlled by a
logic state applied to the SHUT pin. When VSHUT is high,
the device goes into low-power standby mode. This pin is
pulled high internally, it must be externally pulled low to
enable the receiver.
L
SHUNT
L
SERIES
j100
j25
∞
50
0
–j25 –j100
Frequency
(MHz) Z
IN
Z11 S11 L
SHUNT
(nH) L
SERIES
(nH)
300 12-j166 0.803-j0.529 15 72
305 12-j165 0.800-j0.530 15 72
310 12-j163 0.796-j0.536 15 72
315 13-j162 0.791-j0.536 15 72
320 12-j160 0.789-j0.543 15 68
325 12-j157 0.782-j0.550 12 68
330 12-j155 0.778-j0.556 12 68
335 12-j152 0.770-j0.564 12 68
340 11-j150 0.767-j0.572 15 56
345 11-j148 0.762-j0.578 15 56
350 11-j145 0.753-j0.586 12 56
355 11-j143 0.748-j0.592 12 56
360 11-j141 0.742-j0.597 10 56
365 11-j139 0.735-j0.603 10 56
370 10-j137 0.732-j0.612 12 47
375 10-j135 0.725-j0.619 12 47
380 10-j133 0.718-j0.625 10 47
385 10-j131 0.711-j0.631 10 47
390 10-j130 0.707-j0.634 10 43
395 10-j128 0.700-j0.641 10 43
400 10-j126 0.692-j0.647 10 43
405 10-j124 0.684-j0.653 10 39
410 10-j122 0.675-j0.660 10 39
415 10-j120 0.667-j0.667 10 39
420 10-j118 0.658-j0.673 10 36
425 10-j117 0.653-j0.677 10 36
430 10-j115 0.643-j0.684 10 33
435 10-j114 0.638-j0.687 10 33
440 8-j112 0.635-j0.704 8.2 33
Table 4. Input Impedance vs. Frequency
Micrel, Inc. MICRF002/RF022
July 2008 12
M9999-070808
Power Supply Bypass Capacitors
V
DDBB
and V
DDRF
should be connected together directly at
the IC pins. Supply bypass capacitors are strongly
recommended. They should be connected to V
DDBB
and
V
DDRF
and should have the shortest possible lead lengths.
For best performance, connect V
SSRF
to V
SSBB
at the power
supply only (that is, keep V
SSBB
currents from flowing
through the V
SSRF
return path).
Increasing Selectivity with an Optional BandPass
Filter
For applications located in high ambient noise
environments, a fixed value band-pass network may be
connected between the ANT pin and V
SSRF
to provide
additional receive selectivity and input overload protection.
A minimum input configuration is included in Figure 7 it
provides some filtering and necessary overload protection.
Data Squelching
During quiet periods (no signal) the data output (DO pin)
transitions randomly with noise. Most decoders can
discriminate between this random noise and actual data but
for some system it does present a problem. There are three
possible approaches to reducing this output noise:
1. Analog squelch to raise the demodulator threshold
2. Digital squelch to disable the output when data is
not present
3. Output filter to filter the (high frequency) noise
glitches on the data output pin.
The simplest solution is add analog squelch by introducing
a small offset, or squelch voltage, on the C
TH
pin so that
noise does not trigger the internal comparator. Usually
20mV to 30mV is sufficient, and may be achieved by
connecting a several-megohm resistor from the C
TH
pin to
either V
SS
or V
DD
, depending on the desired offset polarity.
Since the MICRF002 has receiver AGC noise at the
internal comparator input is always the same, set by the
AGC. The squelch offset requirement does not change as
the local noise strength changes from installation to
installation. Introducing squelch will reduce sensitivity and
also reduce range. Only introduce an amount of offset
sufficient to quiet the output. Typical squelch resistor values
range from 6.8MΩ to 10MΩ.
Wake-Up Function
The WAKEB output signal can be used to reduce system
power consumption by enabling the rest of a system when
an RF signal is present. The WAKEB is an output logic
signal which goes active low when the IC detects a
constant RF carrier. The wake-up function is unavailable
when the IC is in shutdown mode.
To activate the Wake-Up function, a received constant RF
carrier must be present for 128 counts or the internal
system clock. The internal system clock is derived from the
reference oscillator and is 1/256 the reference oscillator
frequency. For example:
f
T
= 6.4MHz
f
S
= f
T
/256 = 25kHz
P
S
= 1/f
S
= 0.04ms
128 counts x 0.04ms = 5.12ms
where:
f
T
= reference oscillator frequency
f
S
= system clock frequency
P
S
= system clock period
The Wake-Up counter will reset immediately after a
detected RF carrier drops. The duration of the Wake-Up
signal output is then determined by the required wake up
time plus an additional RF carrier on time interval to create
a wake up pulse output.
WAKEB Output Pulse Time = T
WAKE
+ Additional
RF Carrier On Time
For designers who wish to use the wakeup function while
squelching the output, a positive squelching offset voltage
must be used. This simply requires that the squelch resistor
be connected to a voltage more positive than the quiescent
voltage on the C
TH
pin so that the data output is low in
absence of a transmission.
I/O Pin Interface Circuitry
Interface circuitry for the various I/O pins of the MICRF002
are diagrammed in Figures 1 through 6. The ESD
protection diodes at all input and output pins are not shown.
C
TH
Pin
PHI2B PHI1B
PHI1PHI2
CTH
Demodulator
Signal
2.85Vdc
VDDBB
VSSBB VSSBB
Figure 2. CTH Pin
Figure 2 illustrates the C
TH
pin interface circuit. The C
TH
pin
is driven from a P-channel MOSFET source-follower with
approximately 10µA of bias. Transmission gates TG1 and
TG2 isolate the 6.9pF capacitor. Internal control signals
PHI1/PHI2 are related in a manner such that the
impedance across the transmission gates looks like a
“resistance” of approximately 100kΩ. The dc potential at
the C
TH
pin is approximately 1.6V
Micrel, Inc. MICRF002/RF022
July 2008 13
M9999-070808
C
AGC
Pin
VDDBB
VSSBB
675µA
67.5µA
Compa-
rator
1.5µA
15µA
Timout
CAG
C
Figure 3. CAGC Pin
Figure 3 illustrates the C
AGC
pin interface circuit. The AGC
control voltage is developed as an integrated current into a
capacitor C
AGC
. The attack current is nominally 15µA, while
the decay current is a 1/10th scaling of this, nominally
1.5µA, making the attack/decay time constant ratio a fixed
10:1. Signal gain of the RF/IF strip inside the IC diminishes
as the voltage at C
AGC
decreases. Modification of the
attack/decay ratio is possible by adding resistance from the
C
AGC
pin to either V
DDBB
or V
SSBB
, as desired.
Both the push and pull current sources are disabled during
shutdown, which maintains the voltage across C
AGC
, and
improves recovery time in duty-cycled applications. To
further improve duty-cycle recovery, both push and pull
currents are increased by 45 times for approximately 10ms
after release of the SHUT pin. This allows rapid recovery of
any voltage droop on C
AGC
while in shutdown.
DO and WAKEB Pins
VDDBB
VSSBB
Compa-
rator
10µA
10µA
DO
Figure 4. DO and WAKEB Pins
The output stage for DO (digital output) and WAKEB
(wakeup output) is shown in Figure 4. The output is a 10µA
push and 10µA pull switched-current stage. This output
stage is capable of driving CMOS loads. An external buffer-
driver is recommended for driving high-capacitance loads.
REFOSC Pin
250
200k
Active
Bias
REFOSC
30pF
30pF 30µA
VDDBB
VSSBB
VSSB
B
Figure 5. REFOSC Pin
The REFOSC input circuit is shown in Figure 5. Input
impedance is high (200kΩ). This is a Colpitts oscillator with
internal 30pF capacitors. This input is intended to work with
standard ceramic resonators connected from this pin to the
V
SSBB
pin, although a crystal may be used when greater
frequency accuracy is required. The nominal dc bias
voltage on this pin is 1.4V.
SEL0, SEL1, SWEN, and SHUT Pins
to Interna
l
Circuits
VDDBB
VSSBB
SEL0,
SEL1,
SWEN
Q2
Q3
Q1
VSSBB
SHUT Q4
Figure 6a. SEL0, SEL1, SWEN Pins
to Interna
l
Circuits
VDDBB
VSSBB
SHUT
Q2
Q3
Q1
VSSBB
Figure 6b. SHUT Pin
Control input circuitry is shown in Figures 6a and 6b. The
standard input is a logic inverter constructed with minimum
geometry MOSFETs (Q2, Q3). P-channel MOSFET Q1 is
a large channel length device which functions essentially
as a “weak” pullup to V
DDBB
. Typical pull-up current is 5µA,
leading to an impedance to the V
DDBB
supply of typically
1MΩ.
Micrel, Inc. MICRF002/RF022
July 2008 14
M9999-070808
Applications Example
315MHz Receiver/Decoder Application
Figure 7 illustrates a typical application for the MICRF002
UHF Receiver IC. This receiver operates continuously (not
duty cycled) in sweep mode, and features 6-bit address
decoding and two output code bits.
Operation in this example is at 315MHz, and may be
customized by selection of the appropriate frequency
reference (Y1), and adjustment of the antenna length. The
value of C4 would also change if the optional input filter is
used. Changes from the 1kb/s data rate may require a
change in the value of R1. A bill of materials accompanies
the schematic.
SEL0SEL0 SWEN
VSSRF REFOSC
VSSRF SEL1
ANT CAGC
VDDRF WAKEB
VDDBB SHUT
CTH DO
NC VSSBB
C2
2.2µF
4.8970MHz
Y1
U1 MICRF002
4.7µF
Optional Filter
8.2pF, 16.6nH
pcb foil inductor
1in of 30mil trace
C4
L1
+5V
Supply
Input
C1
4.7µF
A0 VDD
A1 VT
A2 OSC1
A3 OSC2
A4 DIN
A5 D11
A6 D10
A7 D9
U2 HT-12D
VSS D8
R1
68k
R2
1k
Code Bit 0
Code Bit 1
RF
(Analog)
Ground
Baseband
(Digital)
Ground
0.4λmonopole
antenna (11.6in)
6-bit
address
Figure 7. 315MHz, 1kbps On-Off Keyed Recwiver/Decod er
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1 Vishay
(1)
4.7µF, Dipped Tantalum Capacitor 1
C2 Vishay
(1)
2.2µF, Dipped Tantalum Capacitor 1
C3 Vishay
(1)
4.7µF, Dipped Tantalum Capacitor 1
C4 Vishay
(1)
8.2pF, COG Ceramic Capacitor 1
CR1 CSA6.00MG Murata
(2)
6.00MHz, Ceramic Resonator 1
D1 SSF-LX100LID Lumex
(3)
RED LED 1
R1 68k, 1/4W, 5% 1
R2 Vishay
(1)
1k, 1/4W, 5% 1
U1 MICRF002 Micrel, Inc.
(4)
300-440MHz QwikRadio
®
ASK Receiver 1
U2 HT-12D Holtek
(5)
Logic Decoder 1
Notes:
1. Vishay Tel: (203) 268-6261
2. Murata Tel: (800) 241-6574, Fx: (770) 436-3030
3. Lumex Tel: (800) 278-5666, Fx: (847) 359-8904
5. Micrel, Inc.: (408) 944-0800
5. Holtek Tel: (408) 894-9046, Fx: (408) 894-0838
Micrel, Inc. MICRF002/RF022
July 2008 15
M9999-070808
PCB Layout Information
The MICRF002 evaluation board was designed and
characterized using two sided 0.031 inch thick FR4
material with 1 ounce copper clad. If another type of printed
circuit board material were to be substituted, impedance
matching and characterization data stated in this document
may not be valid. The gerber files for this board can be
downloaded from the Micrel website at www.micrel.com.
PCB Silk Screen
PCB Component Side Layout
PCB Solder Side Layout
R2
10k
C3(CTH)
0.047µF
C2
0.1µF
C1
4.7µF
C4(C
AGC
)
4.7µF
Y1
6.7458MHz
MICRF002
REF.OSC.
GND
SHUT
GND
DO
GND
J2
JP2
J5
J4
C5
(Not Placed)
JP3JP1
+5V
GND
J3
J1
RF INPUT
Z2
Squelch
Resistor
(Not Placed)
5
6
7
8
12
11
10
9
1
2
3
4
16
15
14
13
SEL0
VSSRF
VSSRF
ANT
VDDRF
VDDBB
CTH
NC
SWEN
REFOSC
SEL1
CAGC
WAKEB
SHUT
DO
VSSBB
Z1
R1
Z4Z3
Micrel, Inc. MICRF002/RF022
July 2008 16
M9999-070808
Package Information
16-Pin SOIC (M)
8-Pin SOIC (M)
Micrel, Inc. MICRF002/RF022
July 2008 17
M9999-070808
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2003 Micrel, Incorporated.
