December 2006 1 MICRF102
MICRF102 Micrel
MICRF102
QwikRadio™ UHF ASK Transmitter
General Description
The MICRF102 is a single chip Transmitter IC for remote
wireless applications. The device employs Micrel’s latest Qwi-
kRadio™ technology. This device is a true “data-in, antenna-
out” monolithic device. All antenna tuning is accomplished
automatically within the IC which eliminates manual tuning,
and reduces production costs. The result is a highly reliable
yet extremely low cost solution for high volume wireless
applications. Because the MICRF102 is a true single-chip
radio transmitter, it is easy to apply, minimizing design and
production costs, and improving time to market.
The MICRF102 uses a novel architecture where the external
loop antenna is tuned to the internal output stage. This trans-
mitter is designed to comply with worldwide UHF unlicensed
band intentional radiator regulations. The IC is compatible with
virtually all ASK/OOK (Amplitude Shift Keying/On-Off Keyed)
UHF receiver types from wide-band super-regenerative radios
to narrow-band, high performance super-heterodyne receiv-
ers. The transmitter is designed to work with transmitter data
rates from 100 to 20k bits per second.
The automatic tuning, in conjunction with the external resistor,
ensures that the transmitter output power stays constant for
the life of the battery.
When used with Micrel’s family of QwikRadio™ receivers,
the MICRF102 provides the lowest cost and most reliable
remote actuator and RF link system available.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Typical Application
PC
VDD
VSS
REFOSC
ASK
MICRF102
ASK DATA INPUT
RP2
6.8k
0.1µF
4.7µF
RP1
100k
+5V
+5V
Y1
ANTP
ANTN
STBY
100k
C3
12pF 50V
(2.7pF 50V)
C2
8.2pF 50V
(4.7pF 50V)
PCB Antenna
L1
Features
• Complete UHF transmitter on a monolithic chip
• Frequency range 300MHz to 470MHz
• Data rates to 20kbps
• Automatic antenna alignment, no manual adjustment
• Low external part count
• Low standby current <0.04µA
Applications
• Remote Keyless Entry systems (RKE)
• Remote fan/light control
• Garage door opener transmitters
• Remote sensor data links
• Tire Pressure Monitoring System (TPMS)
• Telemetry
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
QwikRadio is a trademark of Micrel, Inc. The QwikRadio ICs were developed under a partnership agreement with AIT of Orlando, Florida
QwikRadio™
Ordering Information
Part Number Temperature
Range
Package
Standard Pb-Free
MICRF102BM MICRF102YM -40°C to +85°C 8-Pin SOIC
MICRF102 Micrel
MICRF102 2 December 2006
Pin Description
Pin Number Pin Name Pin Function
1 PC Power Control Input. The voltage at this pin should be set between 0.15V to
0.35V for normal operation.
2 VDD Positive power supply input for the IC. This pin requires a large capacitor for
ripple decoupling. A 4.7µF is recommended.
3 VSS This pin is the ground return for the IC. A power supply bypass capacitor
connected from VDD to VSS should have the shortest possible path.
4 REFOSC This is the timing reference frequency which is the transmit frequency di-
vided by 32. Connect a crystal (mode dependent) between this pin and VSS,
or drive the input with an AC-coupled 0.5VPP input clock. See “Reference
Oscillator” section in this data sheet. The crystal needs to have a 10pF load
capacitance.
5 STBY Input for transmitter stand by control pin is pulled to VDD for transmit opera-
tion and VSS for stand-by mode. The device requires 0.0 volts to be placed
in stand by.
6 ANTN Negative RF power output to drive the low side of the transmit loop antenna.
The RF output stage is tuned in the data transitions in the ASK pin.
7 ANTP Positive RF power output to drive the high side of the transmit loop antenna.
The RF output stage is tuned in the data transitions in the ASK pin.
8 ASK Amplitude Shift Key modulation data input pin. For CW operation, connect
this pin to VDD. Several transitions of highs and lows are required to tune the
output RF stages.
Pin Confi guration
1PC
VDD
VSS
REFOSC
8 ASK
ANTP
ANTN
STBY
7
6
5
2
3
4
8-Pin SOIC (M)
December 2006 3 MICRF102
MICRF102 Micrel
Electrical Characteristics (Note 4)
Specifi cations apply for 4.75V < VDD < 5.5V, VPC = 0.35V, TA = 25°C, freqREFOSC = 12.1875MHz, STBY = VDD. Bold values indicate
-40°C ≤ TA ≤ 85°C unless otherwise noted.
Parameter Condition Min Typ Max Units
Power Supply
Standby Supply Current, IQ V
STBY < 0.5V, VASK < 0.5V or VASK > VDD – 0.5V 0.04 µA
MARK Supply Current, ION @315MHz, Note 5 6 10.5 mA
@433MHz, Note 5 8 12 mA
SPACE Supply Current, IOFF @315MHz 4 6 mA
@433MHz 6 8.5 mA
Mean Operating Current 33% mark/space ratio at 315MHz, Note 5 4.7 mA
33% mark/space ratio at 433MHz, Note 5 6.7 mA
RF Output Section and Modulation Limits:
Output Power Level, POUT @315MHz; Note 5, Note 6 –4 dBm
@433MHz; Note 5, Note 6 –4 dBm
Harmonics Output, Note 7 @315MHz 2nd harm. –46 dBc
3rd harm. –45
@433 MHz 2nd harm. –50 dBc
3rd harm. –41
Extinction Ratio for ASK 40 52 dBc
Varactor Tuning Range Note 8 3 5 7 pF
Reference Oscillator Section
Reference Oscillator Input 300 kΩ
Impedance
Reference Oscillator Source 6 µA
Current
Reference Oscillator Input 0.2 0.5 V
PP
Voltage (peak-to-peak)
Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
Note 4. Specifi cation for packaged product only.
Note 5. Supply current and output power are a function of the voltage input on the PC (power control) pin. All specifi cations in the “Electrical Charac-
teristics” table applies for condition VPC = 350mV. Increasing the voltage on the PC pin will increase transmit power and also increase MARK
supply current. Refer to the graphs “Output Power Versus PC Pin Voltage” and “Mark Current Versus PC Pin Voltage.”
Note 6. Output power specifi ed into a 50Ω equivalent load using the test circuit in Figure 2.
Note 7. The MICRF102 was tested to be compliant to part 15.231 for maximum allowable TX power. The transmitted power is measured 3 meters
from the antenna using transmitter board TX102-2A in Figure 1. Measurement results are summarized in Table 1.
Note 8. The Varactor capacitance tuning range indicates the allowable external antenna component variation to maintain tun-over-normal production
tolerances of external components. Guaranteed by design, not tested in production.
Absolute Maximum Ratings (Note 1)
Supply Voltage(VDD) ...................................................... +6V
Voltage on I/O Pins ...............................VSS–0.3 to VDD+0.3
Storage Temperature Range ................... –65°C to + 150°C
Lead Temperature (soldering, 10 seconds) ............ + 300°C
ESD Rating ............................................................... Note 3
Operating Ratings (Note 2)
Supply Voltage (VDD) ......................................4.75V to 5.5V
Maximum Supply Ripple Voltage ................................ 10mV
PC Input Range .............................. 150mV < VPC < 350mV
Ambient Operating Temperature (TA) .......... -40°C to +85°C
Programmable Transmitter Frequency Range:
......................................................300MHz to 470MHz
MICRF102 Micrel
MICRF102 4 December 2006
Parameter Condition Min Typ Max Unit
Digital / Control Section
Calibration Time Note 9, ASK data rate 20kbps 25 ms
Power Amplifi er Output Hold Off Note 10, STDBY transition from LOW to HIGH 6 ms
Time from STBY Crystal, ESR < 20Ω
Transmitter Stabilization Time From External Reference (500mVpp) 10 ms
from STBY Crystal, ESR < 20Ω 19 ms
Maximum Data Rate
– ASK modulation Duty cycle of the modulating signal = 50% 20 kbits/s
VSTBY Enable voltage 0.75VDD 0.6VDD V
STBY Sink Current ISTBY = VDD 5 6.5 µA
ASK pin VIH, input high voltage 0.8VDD V
V
IL, input low voltage 0.2VDD V
ASK input current ASK = 0V, 5.0V input current –10 0.1 10 µA
Note 9. When the device is fi rst powered up or it loses power momentarily, it goes into the calibration mode to tune up the transmit antenna.
Note 10. After the release of the STDBY, the device requires an initialization time to settle the REFOSC and the internal PLL. The fi rst MARK state
(ASK HIGH) after exit from STDBY needs to be longer than the initialization time. After that, highs and lows in the ASK pin callibrates the
output RF stage. See Figures 2, 3, and 4.
PC
VDD
VSS
REFOSC
ASK
MICRF102
R2
6.8k
C1
0.1µF
16V
+5VSW
R1
100k
ANTP
ANTN
STBY
+5VTX
R3
100k
R5
0Ω
C3
12pF 50V
(2.7pF 50V)
C2
8.2pF 50V
(4.7pF 50V)
L1
pcbant
C5
4.7µF
6.3V
C6 (np)
4.7µF
6.3V Y1
9.84375MHz
(13.560MHz)
C4
100pF
50V
R4
(np)
+5VSW
+5VTX
REFOSC
Data
Figure 1.
Frequency Antenna Height Azimuth EMI Meter Duty Cycle Corrected Corrected 15:231b Limit Margin
(MHz) Polarity (meters) (0-360) Reading Correction Reading Reading (dBµV/m) (dB)
(dBµV/m) (dB) (dBµV/m) (µV/m)
434.03 V 2.5 140 64.2 5.4 58.8 871.00 80.8 22
868.5 V 1 150 53.1 5.4 47.7 242.70 60.8 33.1
434.03 H 1 150 76.1 5.4 70.7 3427.80 80.8 10.1
868.5 H 1.5 295 60.1 5.4 54.7 543.30 60.8 26.1
1302 V 1 195 41.1 5.4 35.7 61.00 54 18.3
1736 V 1 280 51.3 5.4 45.9 197.20 60.8 14.9
1302 H 2.5 110 49.4 5.4 44 158.50 54 10
1736 H 1 113 44.5 5.4 39.2 91.20 60.8 21.6
Note. Higher order harmonics were found to be below the noise fl oor of the receiving system for testing.
Table 1. Transmitted Power Measurement with Transmitted Frequency 433.92MHz, FCC Limits and Compliance
December 2006 5 MICRF102
MICRF102 Micrel
0
5
10
15
20
25
0 100 200 300 400 500 600
CURRENT (mA)
VPC (mV)
Mark Current vs.
PC Pin Voltage
-35
-30
-25
-20
-15
-10
-5
0
5
0 100 200 300 400 500 600
OUTPUT POWER (dBm)
VPC (mV)
Output Power vs.
PC Pin Voltage
Typical Characteristics
RF Output Callibration Time
Figure 2. RF Out CAL Time Example (45ms)
Ch 1 - ASK Pin, 1ms Period
Ch 2 RF Field
Figure 3. RF Out CAL Time Example from Standby
cycle (15ms)
Ch 1 - ASK Pin, 1ms Period
Ch 2 RF Field
Figure 4. RF Out after shut down cycle example (11ms)
Ch 1 - ASK pin, 1ms period
Ch 2 RF Field, ch 4 - Standby Pin
MICRF102 Micrel
MICRF102 6 December 2006
Functional Description
The block diagram illustrates the basic structure of the
MICRF102. Identifi ed in the fi gure are the principal functional
blocks of the IC, namely the (1, 2, 3, 4, 5) UHF Synthesizer,
(6a/b) Buffer, (7) Antenna tuner, (8) Power amplifi er, (9) TX
bias control, (10) Reference bias and, (11) Process tuner.
The UHF synthesizer generates the carrier frequency with
quadrature outputs. The in-phase signal (I) is used to drive
the PA and the quadrature signal (Q) is used to compare the
antenna signal phase for antenna tuning purposes.
The Antenna tuner block senses the phase of the transmit
signal at the antenna port and controls the varactor capacitor
to tune the antenna.
The Power control unit senses the antenna signal and con-
trols the PA bias current to regulate the antenna signal to
the transmit power.
Block Diagram
TX
Bias
Control
Varactor
Device
Antenna
Tuning
Control
Power
Amp
Buffer
VSS
ANTM
ANTP
ASK
Buffer
Prescaler
Divide
by 32
REF.OSC
PC
VDD
VDD
(10)
(5)
(2)
Reference
Oscillator (1)
VCO (4)
(3)
(9)
(8)
(7)
(11)
(6a)
(6b)
STBY Reference
Bias
Phase
Detector
The Process tune circuit generates process independent bias
currents for different blocks.
A PCB antenna loop coupled with a resonator and a resistor
divider network are all the components required to construct
a complete UHF transmitter for remote actuation applications
such as automotive keyless entry.
Included within the IC is a differential varactor that serves
as the tuning element to insure that the transmit frequency
and antenna are aligned with the receiver over all supply and
temperature variations.
December 2006 7 MICRF102
MICRF102 Micrel
Applications Information
Design Process
The MICRF102 transmitter design process is as follows:
1) Set the transmit frequency by providing the cor-
rect reference oscillator frequency.
2) Ensure antenna resonance at the transmit fre-
quency by:
L
ANT = 0.2 × Length × ln(Length/d - 1.6) × 10-9 × k
Where:
Length is the total antenna length in mm.
d is the trace width in mm.
k is a frequency correction factor.
L
ANT is the approximate antenna inductance in
henries.
Note 1. The total inductance, however, will be a little greater
than the LANT calculated due to parasitics. A 2nH should be
added to the calculated value. The LANT formula is an ap-
proximated way to calculate the inductance of the antenna.
The inductance value will vary however, depending on PCB
material, thickness, ground plane, etc. The most precise way
to measure is to use a RF network analyzer.
3) Calculate the total capacitance using the follow-
ing equation.
CfL
T
ANT
=
×××
()
1
422
ππ
Where:
C
T total capacitance in farads.
π = 3.1416.
f = carrier frequency in hertz.
L
ANT inductance of the antenna in henries.
4) Calculate the parallel and series capacitors,
which will resonate the antenna.
4.1) Ideally for the MICRF102 the series and paral-
lel capacitors should have the same value or as
close as possible.
4.2) Start with a parallel capacitor value and plug in
the following equation.
C
CC C
S
T VAR P
=
−+
()
⎛
⎝
⎜⎞
⎠
⎟
1
11
Where:
C
VAR is the center varactor capacitance (5pF for the
MICRF102) in farads.
C
P is the parallel capacitor in farads.
C
S is the series capacitor in farads.
Repeat this calculation until CS and CP are very close and
they can be found as regular 5% commercial values.
Note 2. Ideally, the antenna size should not be larger than
the one shown in Figure 7. The bigger the antenna area,
the higher the loaded Q in the antenna circuit will be. This
will make it more diffi cult to match the parallel and series
capacitors. Another point to take into consideration is the
total AC rms current going through the internal varactor in
the MICRF102. This current should not exceed 16mA rms.
The parallel capacitor will absorb part of this current if the
antenna dimensions are appropriate and not exaggerated
larger than the one shown here.
Note 3. A strong indication that the right capacitor values
have been selected is the mean current with a 1kHz signal
in the ASK pin. Refer to the “Electrical Characteristics” for
the current values.
Note 4. For much smaller antennas, place a blocking capaci-
tor for the series capacitance (around 100pF to 220pF) and
use the following formula for the parallel capacitance CT =
CP + CVAR. The blocking capacitor is needed to ensure that
no dc current fl ows from one antenna pin to the other.
5) Set PC pin to the desired transmit power.
Reference Oscillator Selection
An external reference oscillator is required to set the transmit
frequency. The transmit frequency will be 32 times the refer-
ence oscillator frequency.
ff
TX REFOSC
=×32
Crystals or a signal generator can be used. Correct reference
oscillator selection is critical to ensure operation. Crystals
must be selected with an ESR of 20Ω or less. If a signal
generator is used, the input amplitude must be greater than
200 mVPP and less than 500 mVPP
.
Antenna Considerations
The MICRF102 is designed specifi cally to drive a loop antenna.
It has a differential output designed to drive an inductive load.
The output stage of the MICRF102 includes a varactor that
is automatically tuned to the inductance of the antenna to
ensure resonance at the transmit frequency.
A high-Q loop antenna should be accurately designed to set
the center frequency of the resonant circuit at the desired
transmit frequency. Any deviation from the desired frequency
will reduce the transmitted power. The loop itself is an induc-
tive element. The inductance of a typical PCB-trace antenna
is determined by the size of the loop, the width of the antenna
traces, PCB thickness and location of the ground plane.
The tolerance of the inductance is set by the manufacturing
tolerances and will vary depending upon how the PCB is
manufactured.
The MICRF102 features automatic tuning. The MICRF102
automatically tunes itself to the antenna, eliminating the need
for manual tuning in production. It also dynamically adapts
to changes in impedance in operation and compensates for
the hand-effect.
Automatic Antenna Tuning
The output stage of the MICRF102 consists of a variable
capacitor (varactor) with a nominal value of 5.0pF tunable
over a range of 3pF to 7pF. The MICRF102 monitors the
phase of the signal on the output of the power amplifi er and
automatically tunes the resonant circuit by setting the varactor
value at the correct capacitance to achieve resonance.
In the simplest implementation, the inductance of the loop
antenna should be chosen such that the nominal value is
MICRF102 Micrel
MICRF102 8 December 2006
resonant at 5pF, the nominal mid-range value of the MICRF102
output stage varactor.
Using the equation:
LfC
=1
422
ππ
If the inductance of the antenna cannot be set at the nominal
value determined by the above equation, a capacitor can
be added in parallel or series with the antenna. In this case,
the varactor internal to the MICRF102 acts to trim the total
capacitance value.
L
ANTENNA
C
VARACTOR
C
P
C
S
Figure 5.
Supply Bypassing
Correct supply bypassing is essential. A 4.7µF capacitor in
parallel with a 100pF capacitor is recommended.
The MICRF102 is susceptible to supply-line ripple, if supply
regulation is poor or bypassing is inadequate, spurs will be
evident in the transmit spectrum.
PC
VDD
VSS
REFOSC
ASK
MICRF102
L
ASK DATA INPUT
Transformer Output to 50½
Impedance Transformation
Network
OFF
ON
RP2
(6.8k)
RP1
(100k)
+5V
Crystal
Z1 Z3
Z2
ANTP
ANTM
STBY
To 50½
Termination of
Spectrum Analyzer
Figure 6. Application Test Circuit For Specifi cation Verifi cation
Transmit Power
The transmit power specifi ed in this datasheet is normalized
to a load of 50Ohm. The antenna effi ciency will determine
the actual radiated power. Good antenna design will yield
transmit power in the range of 67dBµV/m to 80dBµV/m at
3 meters.
The PC pin on the MICRF102 is used to set the transmit
power. The differential voltage on the output of the PA (power
amplifi er) is proportional to the voltage at the PC pin.
With more than 0.35V on the PC pin the output amplifi er
becomes current limited. At this point, further increase in
the PC pin voltage will not increase the RF output power in
the antenna pins. Low power consumption is achieved by
decreasing the voltage in the PC pin, also reducing the RF
output power and maximum range.
Output Blanking
When the device is fi rst powered up, or after a momentary
loss of power, the output is automatically blanked (disabled).
This feature ensures RF transmission only occurs under con-
trolled conditions when the synthesizer is fully operational,
plus preventing unintentional transmission at an undesired
frequency. Output blanking is key to guaranteeing compliance
with UHF regulations by ensuring transmission only occurs
in the intended frequency band.
December 2006 9 MICRF102
MICRF102 Micrel
Design Examples
Complete reference designs including gerber fi les can be
downloaded from Micrel’s website at: www.micrel.com/prod-
uct-info/qwikradio.shtml.
Antenna Characteristics
In this design, the desired loop inductance value is determined
according to the table below.
Freq. R XL Ind Q K
(MHz) (Ω) (Ω) (nH) (XL/R)
300 1.7 84.5 44.8 39.72 0.83
315 2.34 89.3 45.1 39.65 0.85
390 3.2 161 47.4 52.00 0.90
434 2.1 136 50.0 78.33 0.96
The reference design, shown in Figure 7, has an antenna
meeting this requirement.
Figure 7. Demo Board PCB.
Loop antennas are often considered highly directional. In
fact small loop antennas can achieve transmit patterns close
in performance to a Dipole antenna. The radiation pattern
below is the theoretical radiation pattern for the antenna, as
shown in Figure 8.
E-total, phi = 0¡
E-total, phi = 90¡
(180-phi) direction phi direction
30.0
180.0
60.0
120.0
150.0
150.0
120.0
60.0
30.0
0.0
Figure 8. Polar Elevation Pattern at 315MHz.
The 0 degree plot is the radiation pattern in the plane of the
transmitter PCB, the 90 degree plot represents the plane
perpendicular to the PCB. Micrel’s evaluation of the perfor-
mance of the board in Figure 8 indicates an even more uniform
radiation pattern that the theoretical plot shown here.
Supply Bypassing
Supply bypassing consists of three capacitors; C3 = 4.7µF,
C4 = 0.1µFand C5 = 100pF
C4
0.1µF
16V
C5
100pF
50V
C3
4.7µF
16V
+5VTX
VDD
VSS
MICRF102
2
3
PC1ASK 8
ANTP 7
ANTM 6
SB 5REFOSC4
Figure 9. Supply Bypassing
Example to Calculate CS and CP Antenna Inductance
Calculation
Length_mils = 2815
dmils = 70
k = 0.85
Length Length_mils 25.4
1000
Length 71.501
=×
()
=
ddmils
d
=×
()
=
25 4
1000
1 778
.
.
L 0.2 Length ln Length
d1.6 10 k
L4410
9
9
=× × −
⎛
⎝
⎜⎞
⎠
⎟××
=×
−
−
Where Length and d are in mm and L is in H;
Where k is a constant dependent on PCB material, copper
thickness, etc.
MICRF102 Series Capacitor Calculation:
f = 315 × 106
L = 46 × 10-9
C
VAR = 5 × 10-12
C
P = 12 × 10-12
CfL
C
T
T
=×××
=×
−
1
4
2 587 10
22
12
ππ
.
C
CC
C
SERIES
TVAR
SERIES
=
−
=×
−
1
11
82 10 12
.
MICRF102 Series Capacitor Calculation:
f = 433.92 × 106
L = 52 × 10-9
C
VAR = 5 × 10-12
C
P = 2.7 × 10-12
CfL
C
T
T
=×××
=×
−
1
4
2 587 10
22
12
ππ
.
MICRF102 Micrel
MICRF102 10 December 2006
C
CC C
C
SERIES
T VAR P
SERIES
=
−+
=×
−
1
11
39 10 12
.
L1 = 52 × 10-9
f1 = 433.92 ¥ 106
CfL
C
T
T
122
1
12
1
41
2 587 10
=×××
=×
−
ππ
.
December 2006 11 MICRF102
MICRF102 Micrel
Package Information
8-Pin SOIC (M)
MICRF102 Micrel
MICRF102 12 December 2006
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 datasheet 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 specifi cations at any time without notifi cation 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 signifi cant injury to the user. A Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2006 Micrel, Incorporated.
