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MICRF104
Micrel
MICRF104
1.8V, QwikRadioTM UHF ASK Transmitter Final Information
General Description
The MICRF104 is a low voltage Transmitter IC for remote wireless applications. The device employs Micrel's latest QwikRadioTM technology. This device is a true "data-in, antenna-out" 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. The MICRF104 incorporates a DC/DC converter to boost the input voltage up to 5V for the RF portion of the IC. This feature enables the MICRF104 to operate off supply voltages as low as 1.8V and transmit at power in excess of -2dBm. The MICRF104 uses a novel architecture where the external loop antenna is tuned to the internal UHF synthesizer. This transmitter is designed to comply 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 receivers. 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, insures that the transmitter output power stays constant for the life of the battery. When coupled with Micrel's family of QwikRadioTM receivers, the MICRF104 provides the lowest cost and most reliable remote actuator and RF link system available.
Features
* * * * * Complete UHF transmitter on a chip Frequency range 300MHz to 470MHz Data rates to 20kbps Automatic antenna alignment, no manual adjustment Low external part count
Applications
* * * * Remote Keyless Entry Systems (RKE) Remote Fan/Light Control Garage Door Opener Transmitters Remote Sensor Data Links
Ordering Information
Part Number MICRF104BM Temperature Range 0C to +85C Package 14-Pin SOIC
Typical Application
L1 22H
MICRF104
1.8V to 4V Supply
1
10F
2 3 4 5
VDDPWR VSS 5V VSS REFOSC
EN VSS SW PC
14 13 12
0.1F
11
100pF 10F
Power Control
VDDRF
RF Standby
6 7
10 9
RFSTBY ANTM
ASK ANTP
8
DATA IN
LOOP ANTENNA
(PCB TRACE)
Figure 1
QwikRadio is a trademark of Micrel, Inc. The QwikRadio ICs were developed under a partnership agreement with AIT of orlando, Florida Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com
November 8, 2001
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MICRF104
MICRF104
Micrel
Pin Configuration
VDDPWR 1 VSS 2 5V 3 VSS 4 REFOSC 5 RFSTBY 6 ANTM 7 14 EN 13 VSS 12 SW 11 PC 10 VDDRF 9 ASK 8 ANTP
MICRF104BM
Pin Description
Pin Number 1 2, 4, 13 3 5 Pin Name VDDPWR VSS 5V REFOSC Pin Function Positive power supply input for the DC/DC converter. Ground return 5V Output from the DC / DC converter This is the timing reference frequency which is the transmit frequency divided 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 Input for transmitter standby control pin is pulled to VDDRF for transmit operation and VSS for stand-by mode. Negative RF power output to drive the low side of the transmit loop antenna Positive RF power output to drive the high side of the transmit loop antenna Amplitude Shift Key modulation data input pin. Positive power supply input for the RF circuit. A power supply bypass capacitor connected from VDDRF to VSS should have the shortest possible path. Power Control Input. The voltage at this pin should be set between 0.3V to 0.4V for normal operation. DC/DC converter Switch. NPN output switch transistor collector. Chip Enable input. Active high
6 7 8 9 10
RFSTBY ANTM ANTP ASK VDDRF
11 12 14
PC SW EN
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MICRF104
Micrel
Absolute Maximum Ratings (Note 1)
Supply Voltage(VDDPWR, VDDRF) .................................. +6V Voltage on I/O Pin EN .................................................. [tbd] Voltage on I/O Pins, RFSTBY, ASK, PC, ANTP, ANTM VSS-0.3 to VDD+0.3 Storage Temperature Range ................... -65C to + 150C Lead Temperature (soldering, 10 seconds) ........... + 300C ESD Rating .............................................................. Note 3
Operating Ratings (Note 2)
Supply Voltage (VDDPWR) .................................. 1.8V to 4V PC Input Range .................................. 0.15V < VPC < 0.35V Ambient Operating Temperature (TA) ............ 0C to +85C Programmable Transmitter Frequency Range: 300MHz to 470MHz
Electrical Characteristics
Specifications apply for VDDPWR = 1.8V, VPC = 0.35V, freqREFOSC = 12.1875MHz, RFSTBY = VDDRF, EN = VDDPWR. TA = 25C, bold values indicate 0C TA 85C unless otherwise noted. Parameter Power Supply Shutdown current, IVDDPWR RF Standby supply, IVDDPWR RF Standby supply, IVDDPWR MARK supply current, ION SPACE supply current, IOFF VDDPWR = 4V Mean operating current 33% mark/space ratio, Note 4 33% mark/space ratio, VDDRWR = 4V, Note 4 5V Max. output current Note 9, VDDPWR = 4V 5V Output Voltage range Note 9 RF Output Section and Modulation Limits: Output power level, POUT Transmitted Power @315MHz; Note 4, Note 5 @433MHz; Note 4, Note 5 @315MHz @433MHz Harmonics output @ 315MHz @433 MHz Extinction ratio for ASK Varactor tuning range Reference Oscillator Section Reference Oscillator Input Impedance Reference Oscillator Source Current Reference Oscillator Input Voltage (peak to peak) 0.2 300 6 0.5 k A VPP Note 7 2nd harm. 3rd harm. 2nd harm. 3rd harm. 40 5 -2 -2.5 tbd tbd -46 -45 -50 -41 52 6.5 8 dBm dBm V/m V/m dBc dBc dBc pF 15 35 4.75 5.25 EN = RFSTBY = VSS RFSTBY = VSS, EN = VDDPWR RFSTBY = VSS, EN = VDDPWR = 4V Note 4, Note 4, VDDPWR = 4V 50 1.5 0.6 31 12 22 9 25 10 41 17 30 12 34 14 A mA mA mA mA mA mA mA mA mA mA V Condition Min Typ Max Units
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MICRF104
MICRF104
Parameter Digital / Control Section Calibration time Power amplifier output hold off time from STBY Transmitter Stabilization Time From STBY Maximum Data rate - ASK modulation VRFSTBY Enable Voltage STBY Sink Current VEN Enable Voltage EN pin current ASK pin VIH, input high voltage VIL, input low voltage ASK input current
Note 1. Note 2. Note 3. Note 4.
Micrel
Condition Min Typ Max Units
Note 8, ASK=HIGH Note 9, STDBY transition from LOW to HIGH Crystal, ESR < 20 From External Reference (500mVpp) Crystal, ESR < 20 Duty cycle of the modulating signal = 50% 20
25 6 10 19
ms ms ms ms kbits/s V 6.5 A V 0.3 V A V 0.2VDDRF V A
0.75VDDRF 0.6VDDRF 5 High Low -10 0.8VDDRF -10 0.1 0.95VDDPWR
10
ASK = 0V, 5.0V input current
10
Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Supply current and output power are a function of the voltage input on the PC (power control) pin. All specifications in the Electrical Characteristics 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." Output power specified into a 50 equivalent load using the test circuit in Figure 5. Transmitted power measured 3 meters from the antenna using transmitter board TX102-2A in Figure 6. The Varactor capacitance tuning range indicates the allowable external antenna component variation to maintain tune over normal production tolerances of external components. Guaranteed by design not tested in production. When the device is first powered up or it loses power momentarily, it goes into the calibration mode to tune up the transmit antenna. After the release of the STDBY, the device requires an initialization time to settle the REFOSC and the internal PLL. The first MARK state (ASK HIGH) after exit from STDBY needs to be longer than the initialization time. The subsequent low to high transitions will be treated as data modulation whereby the envelope transition time will apply.
Note 5. Note 6. Note 7. Note 8. Note 9.
Note 10. The MICRF102 was tested to be Compliant to Part 15.231 for maximum allowable TX power, when operated in accordance with a loop antenna described in Figure 6.
MICRF104
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MICRF104
Micrel
Typical Characteristics
Output Power vs PC Pin Voltage
5 OUTPUT POWER (dBm) 0
CURRENT (mA)
Mark Current vs PC Pin Voltage
25 20 15 10 5 0 0
-5 -10 -15 -20 -25 -30 -35 0 100 200 300 400 500 600 VPC (mV)
100 200 300 400 500 600 VPC (mV)
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MICRF104
MICRF104
Micrel
Functional Diagram
VDDPWR
Oscillator SW
Thermal Shutdown EN Enable Logic Driver
5V
Error Amplifier
1.2V
Bandgap Reference VSS DC/DC Converter
STBY VDD
Reference Bias
(10)
ASK
VDDRF
TX Bias Control
(9)
Power Amp
(8)
ANTP ANTM
PC
Prescaler Divide by 32
(5)
Buffer
(6a)
Phase Detector
VCO (4) (2) (3)
Buffer
(6b)
Antenna Tuning Control
(7)
Varactor Device REF.OSC
Reference Oscillator (1) (11)
VSS
RF Transmitter
Figure 2. MICRF104 Block Diagram (RF Circuit)
Functional Description
The block diagram illustrates the basic structure of the RF portion of the MICRF104. Identified in the figure 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 amplifier, (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 purpose. MICRF104 6
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 controls the PA bias current to regulate the antenna signal to the transmit power. 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
November 8, 2001
MICRF104
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.
Micrel
November 8, 2001
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MICRF104
MICRF104
Micrel
The tolerance in the antenna inductance combined with the tolerance of the capacitor in parallel with it will result in significant differences in resonant frequency from one transmitter to another. Many conventional loop antenna transmitters use a variable capacitor for manual tuning of the resonant circuit in production. Manual tuning increases cost and reduces reliability. A capacitor correctly tuned during manufacture may drift over time and temperature. A change in capacitance will alter the resonant frequency and reduce radiated power. In addition, a hand close to the antenna will alter the resonant properties of the antenna and de-tune it. The MICRF104 features automatic tuning. The MICRF104 automatically tunes itself to the antenna, eradicating 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 MICRF104 consists of a variable capacitor (varactor) with a nominal value of 6.5pF tunable over a range from 5pF to 8pF. The MICRF104 monitors the phase of the signal on the output of the power amplifier 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 resonant at 6.5pF, the nominal mid-range value of the MICRF104 output stage varactor. Using the equation:
L= 1 4 2 f 2C
Applications Information
Design Process The MICRF104 transmitter design process is as follows: 1). Set the transmit frequency by providing the correct reference oscillator frequency 2). Ensure antenna resonance at the transmit frequency by: a. Either, matching antenna inductance to the center of the tuning range of the internal varactor. b. Or, matching capacitance with the antenna inductance by adding an external capacitor (in series with, or in parallel with, the internal varactor) 3). Set PC pin for 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 reference oscillator frequency.
fTX = 32 x fREFOSC
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 20 Ohms or less. If a signal generator is used, the input amplitude must be greater than 200 mVP-P and less than 500 mVP-P. Antenna Considerations The MICRF104 is designed specifically to drive a loop antenna. It has a differential output designed to drive an inductive load. The output stage of the MICRF104 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 inductive 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 how the PCB is manufactured. In the simplest implementation a single capacitor in parallel with the antenna will provide the desired resonant circuit.
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 MICRF104 acts to trim the total capacitance value.
CVARACTOR
CEXTERNAL
LANTENNA
Figure 4. Starting with the inductance of the antenna the capacitance value required to achieve resonance can be calculated. For example a 315MHz transmitter with a 45.1nH inductance antenna will require no capacitor in parallel with the antenna, only the internal varactor that will be tuned to 5.66pF, which is very close to mid range and can be determined using the equation:
C= 1 4 2 f 2L
C
LANTENNA
Figure 3. The resonant frequency is determined by the equation:
f= 1 4 CL
2
Where: f = 315Mhz
MICRF104
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November 8, 2001
MICRF104
L = 45.1nH The value of the capacitor is calculated as 5.66pF. Supply Bypassing Correct supply bypassing is essential. A 4.7uF capacitor in parallel with a 100pF capacitor is required and an additional 0.1F capacitor in parallel is recommended. The MICRF104 is susceptible to supply-line ripple, if supply regulation is poor or bypassing is inadequate, spurs will be evident in the transmit spectrum. Transmit Power The transmit power specified in this datasheet is normalized to a 50Ohm load. The antenna efficiency will determine the actual radiated power. Good antenna design will yield transmit power in the range of 67dBV/m to 80dBV/m at 3 meters. The PC pin on the MICRF104 is used to set the transmit power. The differential voltage on the output of the PA (power amplifier) is proportional to the voltage at the PC pin.
Micrel
If the PC pin voltage rises above 0.4 V the output power 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 first powered up or after a momentary loss of power the output is automatically blanked (disabled). This feature ensures RF transmission only occurs under controlled conditions when the synthesizer is fully operational, 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.
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MICRF104
MICRF104
Micrel
Package Information
PIN 1
0.154 (3.90)
DIMENSIONS: INCHES (MM)
0.026 (0.65) MAX)
0.050 (1.27) 0.016 (0.40) TYP TYP 0.006 (0.15)
0.193 (4.90) 45 3-6 0.244 (6.20) 0.228 (5.80)
0.057 (1.45) 0.049 (1.25)
0.344 (8.75) 0.337 (8.55)
SEATING PLANE
14-Pin SOIC (M)
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. (c) 2001 Micrel Incorporated
MICRF104
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November 8, 2001

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