MICRF112
QwikRadio® UHF ASK/FSK Transmitter
QwikRadio is a registered trademark of Micrel, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
December 2011 M9999-120911
(408) 944-0800
General Description
The MICRF112 is a high performance, easy to use, single
chip ASK / FSK Transmitter IC for remote wireless
applications in the 300 to 450MHz frequency band. This
transmitter IC is a true “data-in, antenna-out” monolithic
device.
MICRF112 is high performance in three areas: power
delivery, operating voltage, and operating temperature. In
terms of power, the MICRF112 is capable of delivering +10
dBm into a 50Ω load. This power level enables a small
form factor transmitter (lossy antenna) such as a key fob
transmitter to operate near the maximum limit of
transmission regulations. In terms of operating voltage,
the MICRF112 operates from 3.6V to 1.8V. Many
transmitter ICs in the same frequency band stop operating
below 2.0V. The MICRF112 will work with most batteries
to the end of their useful limits. In terms of operating
temperature, the MICRF112 operates from -40°C to
+125°C. This wide operating temperature range makes
MICRF112 an ideal candidate for the demanding
applications such as a tire pressure monitoring system.
The MICRF112 is easy to use. One only needs a
reference frequency (RF carrier frequency divided by 32
times) generated from a crystal with a few additional
external parts to create a complete versatile transmitter.
The MICRF112 operates with ASK/OOK (Amplitude Shift
Keying/On-Off Keyed) UHF receiver types from wide-band
super-regenerative radios to narrow-band, high
performance super-heterodyne receivers. The
MICRF112’s maximum ASK data rate is 50kbps
(Manchester Encoding). It operates with FSK receivers as
well. The chip is designed to support narrow band FSK
(Frequency Shift Modulation) by switching an external
capacitor in parallel with the reference crystal. The
MICRF112’s maximum FSK data rate is 10kbps.
Features
Complete UHF transmitter
Frequency range 300MHz to 450MHz
Data rates up to 50kbps ASK, 10kbps FSK
Output Power to 10dBm
Low external part count
Low standby current <1µA
Low voltage operation (down to 1.8V)
Operate with crystals or ceramic resonators
Applications
Remote Keyless Entry Systems (RKE)
Remote Control (STB, HVAC and Appliances)
Garage Door Opener Transmitters
Remote Sensor Data Links
Infrared Transmitter Replacement
Tire Pressure Monitor System (TPMS)
Ordering Information
Part Number Temp. Range Package
MICRF112YMM10 –40°C to +125°C 10-Pin MSOP
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Typical Application
Figure 1. MICRF112 ASK Key Fob Design
Note: Values in parenthesis are for 315MHz
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Pin Configuration
X
TAL_MOD FSK65
1ASK
XTLIN
XTLOUT
VSS
10 VDD
PAOUT
VSSPA
EN
9
8
7
2
3
4
10-Pin MSOP (M)
Pin Description
Pin Number
MSOP-10 Pin Name Pin Function
1 ASK ASK DATA Input
2 XLIN Reference oscillator input connection.
3 XTLOUT Reference oscillator output connection.
4 VSS Ground
5 XTAL_MOD Reference oscillation modulation port for FSK operation.
6 FSK FSK Data Input
7 EN Chip enable, active high
8 VSSPA PA Ground
9 PA_OUT PA output
10 VDD Positive Power Supply
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Absolute Maximum Ratings (Note 1)
Supply Voltage VDD ...................................................+5.0V
Voltage on PAOUT......................................................+7.2V
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 ........................................ 1.8V to 3.6V
Ambient Operating Temperature (TA) ......–40°C to +125°C
Programmable Transmitter Frequency Range:
....................................................... 300MHz to 450MHz
Electrical Characteristics(Note 4)
Specifications apply for VDD = 3.0V, TA = 25°C, FreqREFOSC = 13.560MHz, EN = VDD. Bold values indicate –40°C to 125°C unless
otherwise noted. 1kbps data rate 50% duty cycle. RL 50ohm load (matched)
Parameter Condition Min Typ Max Units
Power Supply
Standby supply current, Iq EN = VSS .05 1µA µA
@ 315MHz, POUT = +10dBm 11.2 mA Mark Supply Current ION
@ 433.92MHz, POUT = +10dBm 11.2 mA
@ 315MHz 2.7 mA SPACE supply current, IOFF
@ 433.92 MHz 2.7 mA
RF Output Section and Modulation Limits:
@315MHz, Note 4 10.5 dBm
Output power level, POUT
FSK or ASK "mark" @433.92MHz, Note 4 10.5 dBm
@ 630MHz, Note 4 2nd harm. -39 dBc
Harmonics output for 315
MHz @945MHz, Note 4 3rd harm. -53 dBc
@ 867.84MHz, Note 4 2nd harm. -55 dBc
Harmonics output for
433.92 MHz @1301.76MHz, Note 4 3rd harm. -55 dBc
Extinction ratio for ASK 70 dBc
FSK Modulation
Frequency Deviation load capacitor = 10pF, crystal type = HC49/U 22 kHz
Data Rate 10 kbps
ASK Modulation
Data Rate 50 kbps
@315MHz, Note 6 <700 kHz
Occupied Bandwidth @433.92MHz, Note 6 <1000 kHz
VCO Section
@ 100kHz from Carrier -76 dBc/Hz
315 MHz Single Side Band
Phase Noise @ 1000kHz from Carrier -79 dBc/Hz
@ 100kHz from Carrier -72 dBc/Hz
433.92 MHz Single Side
Band Phase Noise @ 1000kHz from Carrier -81 dBc/Hz
Reference Oscillator Section
XTLIN, XTLOUT, XTLMOD Pin capacitance 2 pF
External Capacitance See Schematic C17 & C18 18 pF
Oscillator Startup Time Note 5 Crystal: HC49S 300 µs
Digital / Control Section
Output Blanking STDBY transition from LOW to HIGH 500 µs
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Electrical Characteristics (cont.)
Parameter Condition Min Typ Max Units
High (VIH) 0.8×VDD V
Digital Input (EN, ASK and
FSK) Low (VIL) 0.2×VDD V
High (VIH) 0.05 µA Digital Input Leakage
Current
(EN, ASK and FSK Pins) Low (VIL) 0.05 µA
Under Voltage Lock Out
(UVLO) 1.6 V
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. Measured using Test Circuit in Figure 2.
Note 5. Dependent on crystal
Note 6. RBW = 100kHz, OBW measured at -20dBc.
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Test Circuit
Figure 2. MICRF112 Test Circuit with 50Ω Output
Note 1. Values without parenthesis are for 433.92 MHz and values in parenthesis are for 315MHz
Note 2. C9 = 100pF for external REF-OSC
Note 3. For FSK R1 = 0Ω, R2 = NP, R6 = 100k, and R5 = NP
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Assembly Drawing
MICRF112 50 Ohm Test Board
Top Layer
MICRF112 50 Ohm Test Board
Bottom Layer
MICRF112 50 Ohm Test Board
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Typical Characteristics Using MICRF112, 50Ω test Board
315MHz OBW, ASK = 1kHz
315Mhz OBW, ASK = 50kHz
CW Max Power @ 3V, 315MHz,
ASK = 1kHz, Note 1
RF Spectrum 2nd Harmonic;
Fundamental at 315 MHz
RF Spectrum 3rd Harmonic;
Fundamental at 315 MHz
315MHz, Power Level at Space,
VDD = 3.0V, ASK = 1kHz
Note 1. 1.2dB cable loss.
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315MHz, Zero Span , ASK = 1kHz
315MHz, Zero Span, ASK = 50kHz
315MHz, Phase Noise, ASK = 1kHz,
100kHz Offset, –75.59dBc/Hz
315MHz, Phase Noise, ASK = 1khz,
1MHz Offset, –78.99dBc/Hz
315MHz, Phase Noise, ASK = CW,
100kHz Offset, –74.39dBc/Hz
315MHz, Phase Noise, ASK = CW,
1MHz Offset, –77.28dBc/Hz
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433.92MHz OBW, ASK = 1kHz
433.92MHz OBW, ASK = 50kHz
433.92MHz, CW Max Power @ 3V,
ASK = 1kHz, Note 1
RF Spectrum 2nd Harmonic;
Fundamental at 433.92 MHz
RF Spectrum 3rd Harmonic;
Fundamental at 433.92 MHz
433.92MHz Power Level at Space,
VDD = 3.0V, ASK = 1kHz
Note 1. 1.3dB cable loss.
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433.92MHz Zero Span, 1kHz
433.92ASK Zero Span at 50kHz
433.92MHz Phase Noise, ASK = CW,
100kHz Offset, –81.04dBc/Hz
433.92MHz Phase Noise, ASK = CW,
1MHz Offset, –78.76dBc/Hz
433.92MHz Phase Noise, ASK = 1kHz,
100kHz Offset, –71.73dBc/Hz
433.92MHz Phase Noise, ASK = 1kHz,
1MHz Offset, –81.04dBc/Hz
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Functional Diagram
Figure 3. Functional Block Diagram MICRF112 10 Pin ASK / FSK Version
Functional Description
Figure 3 shows a functional block diagram of the
MICRF112 transmitter. The MICRF112 can be best
described as a phase locked transmitter. The system
can be partitioned into six functional blocks; crystal
oscillator, PLL×32, power amplifier, enable control,
under voltage detect and open drain switch for FSK
operation.
Crystal Oscillator
The reference oscillator is crystal-based Pierce
configuration. It is designed to accept crystals with
frequency from 9.375MHz to 14.0625MHz.
Crystal Oscillator Parameters for ASK Operation
Figure 4 shows a reference oscillator circuit
configuration for ASK operation. The reference oscillator
is capable of driving crystals with ESR range from 20Ω
to 300Ω.
When the ESR of crystal is at 20Ω, the crystal parameter
limits are:
ESR 20Ω
CPAR 2 to 10pF
CMO 10 to 40fF
Figure 4. Reference Oscillator ASK Operation
When the ESR of crystal is at 300Ω, the crystal
parameter limits are:
ESR 300Ω
CPAR 2 to 5pF
CMO 10 to 40fF
CLOAD 10 to 30pF
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Crystal Oscillator for FSK Operation
Figure 5 shows reference oscillator circuit configuration
for FSK operation. To operate the MICRF112 in FSK
mode, one additional capacitor is needed between
XTALOUT pin and XTALMOD pin. Crystal parameters
for FSK operation are the same as ASK operation
except:
When the ESR of crystal is at 20Ω, CFSK + CLOAD
not to exceed 70pF.
When the ESR of crystal is at 300Ω, CFSK +
CLOAD not to exceed 30pF
Figure 5. Reference Oscillator FSK Operation
PLL ×32
The function of PLL×32 is to provide a stable carrier
frequency for transmission. It is a “divided by 32” phase
locked oscillator.
Power Amplifier
The power amplifier serves two purposes: 1) to buffer
the VCO from external elements and 2) to amplify the
phase locked signal. The power amplifier can produce
+10dBm at 3V (typical).
Enable Control
Enable control gates the ASK data. It only allows
transmission when Lock, Amplitude and Under Voltage
Detect conditions are valid.
Under Voltage Detect
“Under voltage detect” block senses operating voltage.
If the operating voltage falls below 1.6V, “under voltage
detect” block will send a signal to “enable control” block
to disable the PA.
Open Drain Switch
Open drain switch is used for FSK operation. FSK data
is fed into the FSK pin. The FSK pin is connected to the
gate of the open drain switch. The open collector is
connected to the XTALMOD pin. In Figure 4, a capacitor
is shown connected from XTALMOD pin to XTALOUT.
When FSK pin goes high, the capacitor between
XTALMOD and XTALOUT pulls the frequency of
REFOSC low .
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Application Information
Figure 6. ASK 433.92MHz and 315MHz
Note: Values in parenthesis are for 315MHz
The MICRF112 is well suited to drive a 50 ohms source,
monopole or a loop antenna. Figure 6 is an example of a
loop antenna configuration. Figure 6 also shows both
315MHz and 433.92MHz ASK configurations for a loop
antenna. Besides using a different crystal, Table 1 lists
modified values needed for the listed frequencies.
Frequency
(MHz)
L1
(nH)
C5
(pF)
L4
(nH)
C7
(p
F)
Y1 (MHz)
315.0 470 10 150 6.8 9.84375
433.92 680 10 82 4.7 13.5600
Table 1
The reference design shown in Figure 6 has an antenna
optimized for using the matching network as described in
Table 1.
Power Control Using External Resistor
R7 is used to adjust the RF output levels which may be
needed to meet compliance. As an example, the
following tables list typical values of conducted RF
output levels and corresponding R7 resistor values for
the 50Ω test board shown in Figure 2. R7 of the TX112
Demo board using the loop antenna can be adjusted for
the appropriate radiated field allowed by FCC or ETSI
compliance. Contact Micrel for suggested values to meet
FCC and ETSI compliances.
R7, Ω Output Power, dBm IDD, mA
0 10 6.7
75 8.5 6.3
100 8.0 6.2
500 1.6 4.13
1000 -3.8 4.87
Output Power Versus External Resistor at 315MHz
R7, Ω Output Power, dBm IDD, mA
0 8.68 7.5
75 8.34 7.33
100 8.02 7.3
500 4.34 6.3
1000 0.42 5.5
Output Power Versus External Resistor at 433.92 MHz
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Output Matching Network
Part of the function of the output network is to attenuate
the second and third harmonics. When matching to a
transmit frequency, care must be taken not only to
optimize for maximum output power but to attenuate
unwanted harmonics.
Layout Issues
PCB Layout is of primary concern to achieve optimum
performance and consistent manufacturing results. Care
must used on orientation of components to ensure they
do not couple or decouple the RF signal. PCB trace
length should be short to minimize parasitic inductance,
(1 inch ~ 20nH). For example, depending on inductance
values, a 0.5 inch trace can change the inductance by as
much as 10%. To reduce parasitic inductance, the use of
wide traces and a ground plane under signal traces is
recommended. Vias with low value inductance should be
used for components requiring a connection-to-ground.
Antenna Layout
Directivity is affected by antenna trace layout. No ground
plane should be under the antenna trace. For consistent
performance, components should not be placed inside
the loop of the antenna. Gerbers for Figure 7, with a
suggested layout, can be obtained on the Micrel web site
at: http://www.micrel.com.
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PCB Board
Assembly Drawing
MICRF112 Demo Board
Top Layer
MICRF112 Demo Board
Bottom Layer
MICRF112 Demo Board
Figure 7. Demo Board PCB
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Figure 8. TX112-1 Demo Board Schematic
Note: Configuration is for ASK operation. Values in parenthesis are for 315MHz
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Functional Description of TX112-1
Evaluation Board.
Figure 7 shows the TX112-1 Demo Board PCB. Figure
8 is a detailed schematic of the TX112-1. Note that
components labeled as NP are to obtain different
configurations including FSK Mode of operation. Table 2
describes each header pin connector used in the demo
board.
Pin Function Name Functional Description
J1-1 VDD 1.8V to 3.6V
J1-2 Ground VSS
J1-3 ASK INPUT Modulating Data Input, ASK or FSK
J2-1 REF-OSC External Reference Input
J2-2 GROUND VSS
J2-3 ENABLE Enable Input, Active High
TX112-1-433.92 ASK Bill of Materials
Item Quantity Ref Part
PCB
Footprint Mfg P/N Manufacturer
1 1 C1 10µF 0805 GRM21BR60J106KE01L muRata
2 1 C2 100pF 0603 GRM1885C1H101JA01D muRata
3 1 C5 10pF 0603 GRM1885C1H100JA01D muRata
4 3 R1,R4,R6 (np)
5 5 C6,C8,C11,C12,C15 (np)
6 1 C7 4.7pF 0603 GRM1885C1H4R7JA01D muRata
7 1 C10 0.1µF 0603 GRM188F51H104ZA01D muRata
8 2 C13,C14 18pF 0603 GRM1885C1H180JA01D muRata
9 2 J1,J2 CON3 TSHR-114-S-02-A-GT
10 1 L1 680nH 0805 0805CS-680XJB Coilcraft
11 1 L4 82nH 0603 0603CS-082NXJB Coilcraft
12 1 L5 ANTENNA
ANTENNA LOOP, Part of
PCB
13 1 R2 100kΩ 0603 CRCW0603100KFKEA Vishay
14 6
R3,R5,R7
R8,JPR1,JPR2 0Ω 0603 CRC06030000Z0EA Vishay
13 1 U1 MICRF112YMM10 MICRF112YM Micrel
14 1 Y1 13.560MHZ XTAL SA-13.5600-F-10-C-3-3 HIB
Table 2
Micrel, Inc. MICRF112
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Tx112-1-315MHz ASK Bill of Materials
Item Quantity Ref Part
PCB
Footprint Mfg P/N Manufacturer
1 1 C1 10µF 0805 GRM21BR60J106KE01L muRata
2 1 C2 100pF 0603 GRM1885C1H101JA01D muRata
3 1 C5 10pF 0603 GRM1885C1H1000JA01D muRata
4 3 R1,R4,R6 (np)
5 5 C6,C8,C11,C12,C15 (np)
6 1 C7 4.7pF 0603 GRM1885C1H6R8JA01D muRata
7 1 C10 0.1µF 0603 GRM188F51H104ZA01D muRata
8 2 C13,C14 18pF 0603 GRM1885C1H180JA01D muRata
9 2 J1,J2 CON3 TSHR-114-S-02-A-GT
10 1 L1 470nH 0805 0805CS-470XJB Coilcraft
11 1 L4 150nH 0603 0603CS-R15XJB Coilcraft
12 1 L5 ANTENNA
ANTENNA LOOP, Part of
PCB
13 1 R2 100kΩ 0603 CRCW0603100KFKEA Vishay
14 6
R3,R5,R7
R8,JPR1,JPR2 0Ω 0603 CRC06030000Z0EA Vishay
13 1 U1 MICRF112YMM10 MICRF112YM Micrel
14 1 Y1
9.84375MHZ
XTAL SA-9.84375-F-10-C-3-3 HIB
Table 3
FSK Operation
Table 2 and 3 describe the ASK operation for 433.92MHz and 315MHz.
Table 4 lists the component values that change between ASK or FSK operation. Please note that use of a high FSK data
rate may excite parasitic resonant modes with some crystal types. Recommended crystals from Table 2 and 3 are good
for both ASK and FSK.
Mode R1 R2 R5 R6 JPR1 JPR2 C8
ASK NP 100kΩ 0Ω NP 0Ω NP NP
FSK 0Ω NP NP 100kΩ NP 0Ω (1)3.3pF
(2)10pF
Notes:
1. C8 = 3.3pF for 1kHz using HC49/U or HC49US type crystals.
2. C8= 10pF for 10kHz using HC49/U, (high profile) only.
Table 4: ASK and FSK Settings
R3 R4
Constant ON 0Ω NP
External Standby Control NP 100kΩ
Table 5: Enable Control (Shutdown)
Micrel, Inc. MICRF112
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Package Information
10-Pin MSOP Package Type (YMM10)
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 at Purchaser’s own risk and Purchaser agrees to
fully indemnify Micrel for any damages resulting from such use or sale.
© 2011 Micrel, Incorporated.
