MICRF102BM

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 QwikRadio™ technology. This device is a true “data-in, antennaout” 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 transmitter 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 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, 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. QwikRadio™ 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 VDD – 0.5V MARK Supply Current, ION @315MHz, Note 5 0.04 6 10.5 mA @433MHz, Note 5 8 12 mA SPACE Supply Current, IOFF @315MHz 4 6 mA 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 @433MHz µA RF Output Section and Modulation Limits: Output Power Level, POUT Harmonics Output, Note 7 @315MHz; Note 5, Note 6 –4 dBm @433MHz; Note 5, Note 6 –4 dBm @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 8 7 pF Reference Oscillator Section Reference Oscillator Input Impedance Reference Oscillator Source Current 0.2 Reference Oscillator Input Voltage (peak-to-peak) 300 kΩ 6 µA 0.5 VPP 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. Specification 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 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 6. Output power specified 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. December 2006 3 MICRF102 MICRF102 Micrel Parameter Condition Min Typ Max Unit Digital / Control Section Calibration Time Note 9, ASK data rate 20kbps 25 ms Power Amplifier Output Hold Off Time from STBY Note 10, 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 20 Duty cycle of the modulating signal = 50% kbits/s STBY Sink Current ISTBY = VDD 0.75VDD 0.6VDD 5 ASK pin VIH, input high voltage 0.8VDD ASK input current ASK = 0V, 5.0V input current Enable voltage VSTBY Note 9. 6.5 µA V VIL, input low voltage –10 V 0.1 0.2VDD V 10 µA 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 10. 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. After that, highs and lows in the ASK pin callibrates the output RF stage. See Figures 2, 3, and 4. +5VSW R1 100k R2 6.8k R3 100k C1 0.1µF 16V PC REFOSC C5 4.7µF 6.3V C6 (np) 4.7µF 6.3V C2 8.2pF 50V (4.7pF 50V) MICRF102 +5VTX C4 100pF 50V Data ASK VDD ANTP VSS ANTN REFOSC STBY C3 12pF 50V (2.7pF 50V) L1 pcbant +5VSW Y1 9.84375MHz (13.560MHz) R4 (np) +5VTX R5 0Ω Figure 1. Frequency Antenna Height Azimuth (MHz) Polarity (meters) (0-360) 434.03 868.5 434.03 868.5 1302 1736 1302 1736 V V H H V V H H 2.5 1 1 1.5 1 1 2.5 1 140 150 150 295 195 280 110 113 EMI Meter Duty Cycle Corrected Reading Correction Reading (dBµV/m) (dB) (dBµV/m) 64.2 5.4 58.8 53.1 5.4 47.7 76.1 5.4 70.7 60.1 5.4 54.7 41.1 5.4 35.7 51.3 5.4 45.9 49.4 5.4 44 44.5 5.4 39.2 Corrected 15:231b Limit Margin Reading (dBµV/m) (dB) (µV/m) 871.00 80.8 22 242.70 60.8 33.1 3427.80 80.8 10.1 543.30 60.8 26.1 61.00 54 18.3 197.20 60.8 14.9 158.50 54 10 91.20 60.8 21.6 Note. Higher order harmonics were found to be below the noise floor of the receiving system for testing. Table 1. Transmitted Power Measurement with Transmitted Frequency 433.92MHz, FCC Limits and Compliance MICRF102 4 December 2006 MICRF102 Micrel Typical Characteristics 25 0 Mark Current vs. PC Pin Voltage 20 -5 CURRENT (mA) OUTPUT POWER (dBm) 5 Output Power vs. PC Pin Voltage -10 -15 -20 -25 15 10 5 -30 -35 0 0 0 100 200 300 400 500 600 VPC (mV) 100 200 300 400 500 600 VPC (mV) RF Output Callibration Time Figure 3. RF Out CAL Time Example from Standby cycle (15ms) Ch 1 - ASK Pin, 1ms Period Ch 2 RF Field Figure 2. RF Out CAL Time Example (45ms) 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 December 2006 5 MICRF102 MICRF102 Micrel Block 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) (3) (6b) Antenna Tuning Control (7) Varactor Device REF.OSC Reference Oscillator (1) (11) VSS Functional Description 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. 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 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 controls the PA bias current to regulate the antenna signal to the transmit power. MICRF102 6 December 2006 MICRF102 Micrel Applications Information 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. 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 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 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 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 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 ) 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 ⎟ + C ) ⎝ T VAR P ⎠ 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 in Figure 7. The bigger the antenna area, the higher the loaded Q in the antenna circuit will be. This will make it more difficult to match the parallel and series December 2006 7 MICRF102 MICRF102 Micrel Transmit Power The transmit power specified in this datasheet is normalized to a load of 50Ohm. 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, 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. resonant at 5pF, the nominal mid-range value of the MICRF102 output stage varactor. Using the equation: L= 1 4π f C 2 2 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 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. +5V ASK DATA INPUT MICRF102 RP1 (100k) PC RP2 (6.8k) Transformer Output to 50½ Impedance Transformation Network ASK VDD ANTP VSS ANTM REFOSC STBY To 50½ Termination of Spectrum Analyzer Z2 L Z1 Z3 ON OFF Crystal Figure 6. Application Test Circuit For Specification Verification MICRF102 8 December 2006 MICRF102 Micrel Design Examples Supply Bypassing Supply bypassing consists of three capacitors; C3 = 4.7µF, C4 = 0.1µFand C5 = 100pF 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 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. +5VTX C4 0.1µF 16V C5 100pF 50V VSS 4 REFOSC 7 C3 4.7µF 16V ANTM 6 SB 5 (Length_mils × 25.4 ) d= (dmils × 25.4) 1000 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 = 1 4 × π × f2 × L 2 C T = 2.587 × 10 −12 120.0 150.0 3 ANTP 1000 d = 1.778 ⎛ Length ⎞ L = 0.2 × Length × ln⎜ − 1.6 ⎟ × 10 −9 × k ⎝ d ⎠ − 9 L = 44 × 10 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. 120.0 VDD 8 Example to Calculate CS and CP Antenna Inductance Calculation Length_mils = 2815 dmils = 70 k = 0.85 Figure 7. Demo Board PCB. (180-phi) direction 2 ASK Figure 9. Supply Bypassing Length = 71.501 60.0 PC MICRF102 Length = 30.0 1 CSERIES = 150.0 180.0 Figure 8. Polar Elevation Pattern at 315MHz. 1 1 1 − C T CVAR CSERIES = 8. 2 × 10 −12 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 8 indicates an even more uniform radiation pattern that the theoretical plot shown here. MICRF102 Series Capacitor Calculation: f = 433.92 × 106 L = 52 × 10-9 CVAR = 5 × 10-12 CP = 2.7 × 10-12 CT = 1 4 × π × f2 × L 2 C T = 2.587 × 10 −12 December 2006 9 MICRF102 MICRF102 CSERIES = Micrel 1 1 1 − C T CVAR + CP CSERIES = 3. 9 × 10 −12 L1 = 52 × 10-9 f1 = 433.92 ¥ 106 1 C T1 = 2 4 × π × f 2 × L1 C T1 = 2.587 × 10 −12 MICRF102 10 December 2006 MICRF102 Micrel Package Information 8-Pin SOIC (M) December 2006 11 MICRF102 MICRF102 Micrel MICREL, INC. TEL 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA + 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 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. © 2006 Micrel, Incorporated. MICRF102 12 December 2006