MICRF102 Micrel MICRF102 QwikRadio™ UHF ASK Transmitter Final Information General Description Features The MICRF102 is a single chip Transmitter IC for remote wireless applications. The device employs Micrel’s latest QwikRadio™ 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 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 QwikRadio™ receivers, the MICRF102 provides the lowest cost and most reliable remote actuator and RF link system available. • • • • • • 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 Ordering Information Part Number Temperature Range Package MICRF102BM –0°C to +85°C 8-Pin SOIC Typical Application +5V 4.7µF ASK DATA INPUT MICRF102 RP1 100k 0.1µF PC RP2 6.8k ASK ANTP LOOP ANTENNA VSS ANTM (PCB TRACE) REFOSC STBY VDD Y1 100k +5V 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 September 2002 1 MICRF102 MICRF102 Micrel Pin Configuration PC 1 8 ASK VDD 2 7 ANTP VSS 3 6 ANTM REFOSC 4 5 STBY MICRF102BM Pin Description Pin Number Pin Name 1 PC 2 VDD Positive power supply input for the IC. 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 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 5 STBY Input for transmitter stand by control pin is pulled to VDD for transmit operation and VSS for stand-by mode. 6 ANTM Negative RF power output to drive the low side of the transmit loop antenna 7 ANTP Positive RF power output to drive the high side of the transmit loop antenna 8 ASK MICRF102 Pin Function Power Control Input. The voltage at this pin should be set between 0.15V to 0.35V for normal operation. Amplitude Shift Key modulation data input pin. For CW operation, connect this pin to VDD 2 September 2002 MICRF102 Micrel Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) 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 Supply Voltage (VDD) .................................... 4.75V to 5.5V Maximum Supply Ripple Voltage ............................... 10mV PC Input Range .............................. 150mV < VPC < 350mV Ambient Operating Temperature (TA) ............ 0°C to +85°C Programmable Transmitter Frequency Range: .................................................... 300MHz to 470MHz Electrical Characteristics Specifications apply for 4.75V < VDD < 5.5V, VPC = 0.35V, TA = 25°C, freqREFOSC = 12.1875MHz, STBY = VDD. Bold values indicate 0°C ≤ TA ≤ 85°C unless otherwise noted. Parameter Condition Min Typ Max Units Power Supply µA Standby Supply Current, IQ VSTBY < 0.5V, VASK < 0.5V or VASK > VDD – 0.5V MARK Supply Current, ION @315MHz, Note 4 6 10.5 mA @433MHz, Note 4 8 12 mA @315MHz 4 6 mA @433MHz 6 8.5 mA SPACE Supply Current, IOFF Mean Operating Current 0.04 33% mark/space ratio at 315MHz, Note 4 4.7 mA 33% mark/space ratio at 433MHz, Note 4 6.7 mA @315MHz; Note 4, Note 5 tbd dBm @433MHz; Note 4, Note 5 tbd dBm @315MHz tbd µV/m @433MHz tbd µV/m RF Output Section and Modulation Limits: Output Power Level, POUT Transmitted Power Harmonics Output, Note 10 @ 315MHz 2nd harm. 3rd harm. –46 –45 dBc @433 MHz 2nd harm. 3rd harm. –50 –41 dBc 40 52 dBc 3 5 Extinction Ratio for ASK Varactor Tuning Range Note 7 7 pF Reference Oscillator Section Reference Oscillator Input Impedance Reference Oscillator Source Current Reference Oscillator Input Voltage (peak to peak) September 2002 0.2 3 300 kΩ 6 µA 0.5 VPP MICRF102 MICRF102 Micrel Parameter Condition Min Typ Max Unit Digital / Control Section Calibration Time Note 8, ASK=HIGH 25 ms Power Amplifier Output Hold Off Time from STBY Note 9, STDBY transition from LOW to HIGH Crystal, ESR < 20Ω 6 ms Transmitter Stabilization Time from STBY From External Reference (500mVpp) 10 ms Crystal, ESR < 20Ω 19 ms Maximum Data Rate – ASK modulation VSTBY Duty cycle of the modulating signal = 50% Enable voltage STBY Sink Current ASK pin 20 0.75VDD 0.6VDD ISTBY = VDD VIH, input high voltage 5 V 6.5 0.75VDD 0.6VDD VIL, input low voltage ASK input current kbits/s V 0.3VDD 0.25VDD ASK = 0V, 5.0V input current –10 0.1 µA 10 V µA 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. 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." Note 5. Output power specified into a 50Ω equivalent load using the test circuit in Figure 5. Note 6. Transmitted power measured 3 meters from the antenna using transmitter board TX102-2A in Figure 6. Note 7. 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. Note 8. When the device is first powered up or it loses power momentarily, it goes into the calibration mode to tune up the transmit antenna. Note 9. 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 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. MICRF102 4 September 2002 MICRF102 Micrel Typical Characteristics Output Power vs PC Pin Voltage Mark Current vs PC Pin Voltage 25 0 -10 -15 -20 -25 15 10 5 -30 -35 0 September 2002 20 -5 CURRENT (mA) OUTPUT POWER (dBm) 5 0 0 100 200 300 400 500 600 VPC (mV) 5 100 200 300 400 500 600 VPC (mV) MICRF102 MICRF102 Micrel Functional Diagram Reference Bias STBY VDD ASK (10) TX Bias Control VDD ANTP Power Amp ANTM (8) (9) Prescaler Divide by 32 PC Buffer (6a) (5) Phase Detector Buffer VCO (4) (2) (6b) (3) Antenna Tuning Control (7) Varactor Device REF.OSC Reference Oscillator (1) (11) VSS Figure 2. MICRF102 Block Diagram Functional Description The block diagram illustrates the basic structure of the MICRF102. 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. 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. MICRF102 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. 6 September 2002 MICRF102 Micrel difficult 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 capacitor 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 flows 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 reference oscillator frequency. Applications Information Design Process The MICRF102 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: LANT = 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. LANT 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 approximated 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 following equation. CT = (4 × π 1 2 × f 2 × L ANT fTX = 32 × 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 MICRF102 is designed specifically 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 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. The MICRF102 features automatic tuning. The MICRF102 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 MICRF102 consists of a variable capacitor (varactor) with a nominal value of 5.0pF tunable over a range from 3pF to 7pF. The MICRF102 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. ) Where: CT total capacitance in farads. π = 3.1416. f = carrier frequency in hertz. LANT 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 parallel 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. CS = 1 1 1 C − (C T VAR + CP ) Where: CVAR is the center varactor capacitance (5pF for the MICRF102) in farads. CP is the parallel capacitor in farads. CS 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 here. The bigger the antenna area, the higher the loaded Q in the antenna circuit will be. This will make more September 2002 7 MICRF102 MICRF102 Micrel In the simplest implementation, the inductance of the loop antenna should be chosen such that the nominal value is resonant at 5pF, the nominal mid-range value of the MICRF102 output stage varactor. Using the equation: L= 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 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 amplifier) is proportional to the voltage at the PC pin. With more than 0.35V on the PC pin the output amplifier 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. 1 4 π 2 f 2C 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. CS CVARACTOR CP LANTENNA Figure 4. Supply Bypassing Correct supply bypassing is essential. A 4.7uF 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. +5V ASK DATA INPUT MICRF102 RP1 (100k) PC RP2 (6.8k) Transformer Output to 50‰ Impedance Transformation Network ASK VDD ANTP VSS ANTM REFOSC STBY To 50‰ Termination of Spectrum Analyzer Z2 L Z1 Z3 ON OFF Crystal Figure 5. Application Test Circuit For Specification Verification MICRF102 8 September 2002 MICRF102 Micrel Supply Bypassing Supply bypassing consists of three capacitors; C3 = 4.7uF, C4 = 0.1uFand C5 = 100pF Design Examples Complete reference designs including gerber files can be downloaded from Micrel’s website at www.micrel.com/product-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 (MHz) (ohms) (ohms) (nH) (XL/R) 300 1.7 84.5 44.8 39.72 315 2.34 89.3 45.1 39.65 390 3.2 161 47.4 52.00 434 2.1 136 50.0 78.33 The reference design shown in Figure 6. has an meeting this requirement. +5VTX C5 100pF 50V C4 0.1 F 16V 0.83 0.85 0.90 0.96 antenna 3 VSS 4 REFOSC ANTP 7 C3 4.7 F 16V ANTM 6 SB 5 (Length_mils × 25.4) 1000 d= (dmils × 25.4) 1000 d = 1.778 Length L = 0.2 × Length × ln − 1.6 × 10 −9 × k d L = 44 × 10 −9 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 shown in Figure 6. 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 CVAR = 5 × 10-12 CP = 12 × 10-12 E-total, phi = 0¡ E-total, phi = 90¡ 0.0 30.0 60.0 phi direction CT = 120.0 l 4 × π × f2 × L 2 C T = 5.55 × 10 −12 120.0 150.0 150.0 CSERIES = 180.0 Figure 7. 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 performance of the board in Figure 6. indicates an even more uniform radiation pattern that the theoretical plot shown here. September 2002 VDD 8 Example to Calculate CS and CP Antenna Inductance Calculation Length_mils = 2815 dmils = 70 k = 0.85 Figure 6 (180-phi) direction 2 ASK Figure 8. Length = 71.501 60.0 PC MICRF102BM K Length = 30.0 1 1 1 1 − C T C VAR CSERIES = 8.2 × 10 −12 9 MICRF102 MICRF102 Micrel MICRF102 Series Capacitor Calculation f = 433.92 × 106 L = 52 × 10-9 CVAR = 5 × 10-12 CP = 2.7 × 10-12 CT = 1 4 × π2 × f2 × L C T = 2.587 × 10 −12 CSERIES = 1 1 1 − C T C VAR + CP CSERIES = 3.9 × 10 −12 L1 = 52 × 10-9 f1 = 433.92 ¥ 106 C T1 = 1 4 × π 2 × f 2 × L1 C T1 = 2.587 × 10 −12 MICRF102 10 September 2002 MICRF102 Micrel Package Information 0.026 (0.65) MAX) PIN 1 DIMENSIONS: INCHES (MM) 0.154 (3.90) 0.193 (4.90) 0.050 (1.27) 0.016 (0.40) TYP TYP 45° 3°–6° 0.063 (1.60) MAX 0.057 (1.45) 0.049 (1.25) 0.197 (5.0) 0.189 (4.8) SEATING PLANE 0.244 (6.20) 0.228 (5.80) 8-Pin SOP (M) September 2002 11 MICRF102 MICRF102 Micrel MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB USA 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. © 2002 Micrel, Incorporated MICRF102 12 September 2002