MICRF218 3.3V, 315/433MHz Wide-IF Bandwidth ASK Receiver General Description Features The MICRF218 is a 3.0V to 3.6V, 300MHz to 450MHz ASK/OOK super-heterodyne receiver with user selectable Intermediate Frequency (IF) Bandwidths of 550kHz or 1500kHz at 433.92MHz, making it an excellent solution for use with low-cost SAW-based transmitters or transmitters which use low-cost, mediumgrade (~30ppm) crystals. The device requires a single, low-cost crystal to select the proper RF frequency, integrated Automatic Gain Control (AGC), data slicer, and programmable baseband filter bandwidths of 1.6kHz to 13kHz allowing the device to support bit-rates up to 20kbps at 433.92MHz. The MICRF218 consumes 4.0mA of supply current at 315MHz and 5.5mA of supply current at 433.92MHz. The device also features a low-power shutdown mode where the device consumes 1A of supply current. The device achieves a sensitivity of -108dBm at 1kbps. For transmitters using higher-quality (~10ppm) crystals, the MICRF219A/MICRF220 offer an IF-bandwidth of 330kHz and a sensitivity of -110dBm at 1kbps, which can provide better sensitivity and longer range performance. Fully integrated 300 to 450MHz ASK/OOK Receiver No external IF Filter Required Wide IF-Bandwidth filter supports reception of SAW based and medium-grade (~30ppm) transmitter Sensitivity at 433.92MHz at 1kbps with 0.1% BER o -108dBm sensitivity with 550kHz IF Bandwidth o -106dBm sensitivity with 1500kHz IF Bandwidth Low-Supply Current o 4.0mA at 315MHz o 5.5mA at 433.92MHz o 1µA low-power shutdown mode Data Rates to 10 kbps (Manchester Encoded) @ 433.92 MHz Duty Cycling Capable > 100:1 (shut down mode) 60dB Analog Received Signal Strength Indicator 16-pin QSOP (4.9mm x 6.0mm) package Ordering Information Part Number Temperature Range Package MICRF218AYQS –40° to +85°C 16-Pin QSOP Application Example Y1 9.8131MHz ANT PCB Pattern 1 C2 1.5pF 50V 2 3 4 +3V L1 39nH C1 6.8pF L2 68nH 5 6 C3 0.1µF 16V 7 8 U1 MICRF218AYQS RO1 RO2 GNDRF NC ANT RSSI GNDRF CAGC VDD CTH IF_BW SEL1 SEL0 DO SHDN GND 16 15 14 RSSI 13 12 11 10 9 DO C4 0.1µF 16V C5 4.7µF 6.3V IF_BW CONTROL QwikRadio is a registered trademark of Micrel, Inc. MLF and MicroLeadFrame are trademarks of Amkor Technology, 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 November 2011 M9999-111111 (408) 944-0800 Micrel MICRF218 315MHz/315.802, 900Hz Baud Rate Example Pin Configuration RO1 GNDRF ANT GNDRF Vdd IF_BW SEL0 SHDN 1 16 2 15 3 14 4 13 5 12 6 11 7 10 8 9 RO2 NC RSSI CAGC CTH SEL1 DO GND MICRF218AYQS Pin Description 16-Pin QSOP Pin Name 1 RO1 2 GNDRF 3 ANT 4 GNDRF 5 VDD 6 IF_BW 7 SEL0 Logic control input with active internal pull-up. Used in conjunction with SEL1 to control the demodulator low pass filter bandwidth. (See filter table for SEL0 and SEL1 in application subsection) 8 SHDN Shutdown logic control input. Active internal pull-up and must be pulled low for Normal Operation. 9 GND Negative supply connection for all chip functions except RF input. 16-Pin QSOP Pin Name Pin Function 10 DO 11 SEL1 Logic control input with active internal pull-up. Used in conjunction with SEL0 to control the demodulator low pass filter bandwidth. (See filter table for SEL0 and SEL1 in application subsection) 12 CTH Demodulation threshold voltage integration capacitor. Capacitor to GND sets the settling time for the demodulation data slicing level. Values above 1nF are recommended and should be optimized for data rate and data profile. 13 CAGC AGC filter capacitor. A capacitor, normally greater than 0.47uF, is connected from this pin to GND 14 RSSI Received signal strength indication output. Output is from a buffer with 200 ohms typical output impedance. 15 NC 16 RO2 November 2011 Pin Function Reference resonator input connection to Colpitts oscillator stage. May also be driven by external reference signal of 1.5V p-p amplitude maximum. Negative supply connection associated with ANT RF input. RF signal input from antenna. Internally AC-Coupled. It is recommended that a matching network with an inductor to RF ground is used to improve ESD protection. Negative supply connection associated with ANT RF input. Positive supply connection for all chip functions. IF bandwidth control logic input. Use VDD for Wide IF Bandwidth or VSS for Narrow IF Bandwidth. This pin must not be left floating, must be tied to VDD or VSS. Demodulated data output. Not Connected Reference resonator connection. 7pF in parallel with low resistance MOS switch to GND during normal operation. Driven by startup excitation circuit during the internal startup control sequence. 2 M9999-111111 (408) 944-0800 Micrel MICRF218 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VDD) .................................................+5V Input Voltage .............................................................+5V Junction Temperature ......................................... +150°C Lead Temperature (soldering, 10sec.) .................. 260°C Storage Temperature (TS) .....................-65ºC to +150°C Maximum Receiver Input Power ........................+10dBm ESD Rating(3) ......................................................... 3KV Supply voltage (VDD)............................ +3.0V to +3.6V Ambient Temperature (TA).................. –40°C to +85°C Input Voltage (VIN) ......................................3.6V (Max) Maximum Input RF Power .............................. –20dBm Operating Frequency.......................... 300 to 450 MHz Electrical Characteristics(4) Specifications apply for VDD = 3.0V, VSS = 0V, CAGC = 4.7uF, CTH = 0.1uF, Bold values indicate –40°C - TA +85°C. Symbol Parameter Condition Min Typ Max Units Continuous Operation, fRX = 315 MHz 4.0 mA IDD Ishut MICRF218 Operating Supply Current 20:1 Duty Cycle, fRX = 315 MHz 0.2 mA Continuous Operation, fRX = 433.92 MHz 5.5 mA 20:1 Duty Cycle, fRX = 433.92 MHz 0.3 mA 1 µA 20 dB fRX = 315 MHz, Narrow IF 0.98 MHz fRX = 433.92 MHz, Narrow IF 1.4 MHz fRX = 315 MHz, Wide IF 1.8 MHz fRX = 433.92 MHz, Wide IF 2.4 MHz Shut down Current RF/IF Section Image Rejection 1st IF Center Frequency 1st IF Center Frequency Receiver Sensitivity @ 1kbps fRX = 315 MHz, Narrow IF (50 ohms) -108 dBm fRX = 433.92 MHz, Narrow IF (50 ohms) -108 dBm Receiver Sensitivity @ 1kbps fRX = 315 MHz, Wide IF (50 ohms) -106 dBm fRX = 433.92 MHz, Wide IF (50 ohms) -106 dBm fRX = 315 MHz, Narrow IF fRX = 433.92 MHz, Narrow IF fRX = 315 MHz, Wide IF fRX = 433.92 MHz, Wide IF 400 550 1000 1500 kHz kHz kHz kHz 16-j211 Ω 9.54-j152 Ω IF Bandwidth Antenna Input Impedance Receive Modulation Duty Cycle November 2011 fRX = 315 MHz fRX = 433.92 MHz Note 6 20 3 80 % M9999-111111 (408) 944-0800 Micrel Symbol MICRF218 Parameter AGC Attack / Decay Ratio Condition Min Typ Max Units tATTACK / tDECAY 0.1 AGC pin leakage current TA = 25ºC ±2 nA TA = +85ºC ± 800 nA AGC Dynamic Range @ fRX = 433.92MHz RFIN @ -50dBm 1.13 V RFIN @ -110dBm 1.70 V 9.8131 MHz 9.78823 MHz 13.5178 MHz 13.48352 MHz Reference Oscillator Frequency fRX = 315 MHz, Narrow IF, IF_BW = VSS Crystal Load Cap = 10pF fRX = 315 MHz, Wide IF, IF_BW = VDD Crystal Load Cap = 10pF fRX = 433.92 MHz Narrow IF, IF_BW = VSS Crystal Load Cap = 10pF fRX = 433.92 MHz Wide IF , IF_BW = VDD Crystal Load Cap = 10pF Input Impedance 300 Input Range Source Current Demodulator CTH Source Impedance CTH Leakage Current Demodulator Filter Bandwidth @ 315 MHz CTH Source Impedance CTH Leakage Current Demodulator Filter Bandwidth @ 433.92 MHz November 2011 0.2 V(REFOSC) = 0V fREFOSC = 9.8131MHz, 315MHz, Note 8 TA = 25ºC TA = +85ºC SEL0=0, SEL1=0 SEL0=0, SEL1=1 SEL0=1, SEL1=0 SEL0=1, SEL1=1 TA = 25ºC TA = +85ºC SEL0=0, SEL1=0 SEL0=0, SEL1=1 SEL0=1, SEL1=0 SEL0=1, SEL1=1 µA 165 kΩ 120 ±2 ± 800 1625 3250 6500 13000 4 Vp-p 3.5 ±2 ± 800 1180 2360 4720 9420 fREFOSC = MHz, 433.92MHz, note 8 kΩ 1.5 nA Hz Hz Hz Hz kΩ nA Hz Hz Hz Hz M9999-111111 (408) 944-0800 Micrel Symbol MICRF218 Parameter Condition Min Typ Max Units Digital / Control Functions Input High Voltage Pins DO (As input), SHDN Input Low Voltage Pins DO (As input), SHDN DO pin output current Output rise and fall times V 0.8VDD 0.2VDD Source @ 0.8 Vdd 260 Sink @ 0.2 Vdd 600 CI = 15 pF, pin DO, 10-90% V µA 2 µsec 0.22 to 2 V RSSI RSSI DC Output Voltage Range RSSI response slope -90 dBm to -40 dBm RSSI Output Current RSSI Output Impedance RSSI Response Time ±1.5 mV/ dBm mA 200 Ω 0.3 Sec 35 50% data duty cycle, input power to Antenna = -20 dBm Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Device are ESD sensitive. Use appropriate ESD precaution. Exceeding the absolute maximum rating may damage the device. 4. Sensitivity is defined as the average signal level measured at the input necessary to achieve 10-2 BER (bit error rate). The input signal is defined as a return-to-zero (RZ) waveform with 50% average duty cycle (Manchester encoded) at a data rate of 1kBPS. Conductive measurement is performed using 50 ohm test circuit . 5. Spurious reverse isolation represents the spurious component that appear on the RF input pin (ANT) measured into 50 Ohms with an input RF matching network. 6. When data burst does not contain preamble, the duty cycle is then defined as total duty cycle, including any “quiet” time between data bursts. When data bursts contain preamble sufficient to charge the slice level on capacitor Cth, then duty cycle is the effective duty cycle of the burst alone. [For example, 100msec burst with 50% duty cycle, and 100msec “quiet” time between bursts. If burst includes preamble, duty cycle is TON/(TON + tOFF) = 50%; without preamble, duty cycle is TON/(TON + TOFF + TQUIET) = 50msec/(200msec) = 25%. TON is the (Average number of 1’s/burst) × bit time, and TOFF = TBURST – TON.) 7. Parameter scales linearly with reference oscillator frequency fT. For any reference oscillator frequency other than one of the tabulated frequencies (called FTAB), compute new parameter value as the ratio: Parameter at fREFOSCMHz = ( fREFOSCMHz /FTAB ) × ( parameter at FTABMHz ) 8. Parameter scales inversely with reference oscillator frequency fT. For any reference oscillator frequency other than one of the tabulated frequencies (called FTAB), compute new parameter value as the ratio: Parameter at fREFOSCMHz = ( FTAB / fREFOSCMHz ) × ( parameter at FTABMHz ) November 2011 5 M9999-111111 (408) 944-0800 Micrel MICRF218 Typical Characteristics November 2011 6 M9999-111111 (408) 944-0800 Micrel November 2011 MICRF218 7 M9999-111111 (408) 944-0800 Micrel MICRF218 LO Leakage in RF Port Re-radiation from MICRF218 Antenna Port November 2011 8 M9999-111111 (408) 944-0800 Micrel MICRF218 Figure 1 Simplified Block Diagram Functional Description Receiver Operation Figure 1 illustrates the basic structure of the MICRF218. It is composed of three sub-blocks; Image Rejection UHF Down-converter with Switch-able Dual IF Bandwidths, the OOK Demodulator, and Reference and Control Logics. Outside the device, the MICRF218 requires only three components to operate: two capacitors (CTH, and CAGC) and the reference frequency device, usually a quartz crystal. Additional five components may be used to improve performance. These are: low cost linear regulator decoupling capacitor, two components for the matching network, and two components for the preselector band pass filter. LNA The RF input signal is AC-coupled into the gate circuit of the grounded source LNA input stage. The LNA is a Cascoded NMOS. Mixers and Synthesizer The LO ports of the Mixers are driven by quadrature local oscillator outputs from the synthesizer block. The local oscillator signal from the synthesizer is placed on the low side of the desired RF signal to allow suppression of the image frequency at twice the IF frequency below the wanted signal. The local oscillator is set to 32 times the crystal reference frequency via a phase-locked loop synthesizer with a fully integrated loop filter. Image Reject Filter and IF Band-Pass Filter The IF ports of the mixer produce quadrature down converted IF signals. These IF signals are low-pass filtered to remove higher frequency products prior to November 2011 9 M9999-111111 (408) 944-0800 Micrel MICRF218 the image reject filter where they are combined to reject the image frequencies. The IF signal then passes through a third order band pass filter. The IF Band-Pass filters are fully integrated inside the MICRF218. After filtering, four active gain controlled amplifier stages enhance the IF signal to proper level for demodulation. frequency may use the wider IF bandwidth by utilizing the appropriate equation (1) or (2) for each crystal frequency. The following circuit, Figure 4, is an example of switched crystal operation. The IF Bandwidth Control and REF-OSC Control allow switching between two operating frequencies with either a narrow bandwidth or a wide bandwidth. In this case, the logic control switches between 390MHz in Wide Band Mode and 315MHz in Narrow Bandwidth Mode. The advantage of this circuit is when a RF interferer is at one frequency, the receiver can go to another frequency to get clear reception. Figure 5 shows PCB layout for MICRF218 with switched crystal operation. Please contact the Micrel RF Application Group for detailed document. IF Bandwidth General Description The MICRF218 has IF filters which may be configured for operation in a narrow band or wide band mode using the IF_BW pin. This pin must not be left floating; it must be tied to VDD or VSS. With the use of a 13.4835MHz crystal and the IF_BW = VDD (wide mode) the IF frequency is set to 2.4MHz with a bandwidth of 1500kHz. With the use of a 13.5178MHz crystal and the IF_BW = VSS (narrow mode) the IF frequency is set to 1.4MHz with a bandwidth of 550kHz at 433.92MHz. The crystal frequency for Wide Bandwidth IF operation is given by: Dual Frequency Configuration Examples: Scenario 1: Frequency 1 - 315MHz Narrow Bandwidth Frequency 2 - 433.92MHz Wide Bandwidth A 9.81314MHz crystal switched in circuit during narrow IF mode, combined with a 13.48352MHz crystal, allows operation at 315MHz with 400kHz IF bandwidth, and at 433.92MHz with 1500kHz bandwidth. Operating Freq MHz (1) 2.178 ) (32 12 The crystal frequency for Narrow Bandwidth IF operation is given by: REFOSC Operating Freq MHz (2) 1.198 ) (32 12 Note: The IF frequency, IF bandwidth, and IF separation between IF_BW modes using a single crystal will scale linearly and can be calculated as follows: REFOSC Scenario 2: Frequency 1 - 315MHz Wide Bandwidth Frequency 2 - 433.92MHz Narrow Bandwidth A 9.78823MHz crystal switched in circuit during Wide IF mode, combined with a 13.51783MHz crystal, allows operation at 315MHz with 1000kHz IF bandwidth, and 433.92MHz with 550kHz IF bandwidth. IF_Parameter IF_Parameter @ 433.92 MHz Operating Freq (MHz) * 433.92(MHz) (3) Scenario 3: Frequency 1 - 315MHz Narrow Bandwidth Frequency 2 - 433.92MHz Narrow Bandwidth A 9.8131MHz crystal switched in circuit, combined with a 13.51783MHz crystal during narrow IF mode, allows operation at 315MHz with 400kHz IF bandwidth, and at 433.92MHz with 550kHz bandwidth. Switched Crystal Application Operation Appropriate choice of two crystal frequencies and IF_BW mode switching allows operation at two different frequencies; one with low bandwidth operation and the other with high bandwidth operation. Either the lower or higher reception November 2011 10 M9999-111111 (408) 944-0800 Micrel MICRF218 J4 IF BANDWIDTH CONTROL J1 1 EXTERNAL REFERENCE OSCILLATOR INPUT 2 REFOSC 1 2 CON2 C1 NP VDD = WIDE BANDWIDTH 0V = NARROW BANDWIDTH +3V J2 RF IN L4 100nH C2 2.2pF 1 L3 100nH 2 3 4 5 +3V C3 33pF L2 3.9nH 6 7 C5 100nF Notes: 1. 0V = Common 2. VDD Input = 3.0 to 3.3V 3. Ref-Osc Control: 0V = 315 MHz Operation, VDD = 390.1 MHz Operation 3.0 to 3.3V 3.0 to 3.3V COM SHDN DO REF-OSC CNTR COM 8 R3 NP U1 MICRF218AYQS RO2 RO1 NC GNDRF ANT RSSI GNDRF CAGC VDD CTH IF_BW SEL1 SEL0 DO SHDN GND R5 100K +3V J3 1 2 3 4 5 6 7 C7 NP 16 JPR1 0 OHMS Y1 9.8131MHz JPR2 NP R1 NP 15 14 TSDF1220W Q1 13 12 9 C4 0.047µF C5 4.7µF R4 0 OHMS R7 100k R11 100k R6 10k R8 10k L3 ZCB-0603 TSDF1220W Q2 R2 NP 11 10 Y2 12.1287MHz R9 10k R10 100k +3V DATA OUT NP = Not Placed Figure 4. Dual Frequency QR218BP_SWREF, 315 MHz and 390 MHz November 2011 11 M9999-111111 (408) 944-0800 Micrel MICRF218 Single Crystal Operation for Dual Frequency Operation Slicer and Slicing Level The signal prior to slicer is still linear demodulated AM. Data slicer converts this signal into digital “1”s and “0”s by comparing with the threshold voltage built up on the CTH capacitor. This threshold is determined by detecting the positive and negative peaks of the data signal and storing the mean value. Slicing threshold is at 50%. After the slicer, the signal is now digital OOK data. During long periods of “0”s or no data period, threshold voltage on the CTH capacitor may be very low. Large random noise spikes during this time may cause erroneous “1”s at DO pin. When using a single crystal, the IF_BW function may be used to switch between two operating frequencies. Bandwidth will scale directly with operating frequency (equation 3). Higher operating frequency will have the wider IF bandwidth. Given one operating frequency, the other frequency can be determined.: Freq2 Narrow Bandwidth Freq1 Wide Bandwidth * (384 1.198) (4) (384 - 2.178) Freq2 Wide Bandwidth Freq1 Narrow Bandwidth * (384 2.178) (5) (384 - 1.198) AGC Comparator The AGC comparator monitors the signal amplitude from the output of the programmable low-pass filter. When the output signal is less than 750mV, the threshold 1.5µA current is sourced into the external CAGC capacitor. When the output signal is greater than 750mV, a 15µA current sink discharges the CAGC capacitor. The voltage developed on the CAGC capacitor acts to adjust the gain of the mixer and the IF amplifier to compensate for RF input signal level variation. OOK Demodulator The following section discusses the Demodulator which is comprised of Detector, Programmable Low Pass Filter, Slicer, and AGC comparator. Detector and Programmable Low-Pass Filter The demodulation starts with the detector removing the carrier from the IF signal. Post detection, the signal becomes baseband information. The programmable low-pass filter further enhances the baseband information through the use of SEL0 and SEL1. There are four programmable low-pass filter BW settings for 433.92MHz operation, see Table 1. Low pass filter BW will vary with RF Operating Frequency. Filter BW values can be easily calculated by direct scaling. See equation below for filter BW calculation: BW Operating Freq BW @433.92MHz * (Operating Freq) 433.92 Reference Control There are two components in Reference and Control sub-block: 1) Reference Oscillator and 2) Control Logic through parallel Inputs: SEL0, SEL1, SHDN and IF_BW. Reference Oscillator (6) It is very important to choose the filter setting that best fits the intended data rate to minimize data distortion. Demod BW is set at 13000Hz @ 433.92MHz as default (assuming both SEL0 and SEL1 pins are floating). The low pass filter can be hardware set by external pins SEL0 and SEL1. SEL0 SEL1 Demod BW (@ 434MHz) 0 0 1625Hz 1 0 3250Hz 0 1 6500Hz 1 1 13000Hz - default Table 1. Demodulation BW Selection Figure 6. Reference Oscillator Circuit The reference oscillator in the MICRF218 (Figure 6) November 2011 12 M9999-111111 (408) 944-0800 Micrel MICRF218 uses a basic Colpitts crystal oscillator configuration with MOS transconductor to provide negative resistance. All capacitors shown in Figure 6 are integrated inside the MICRF218. R01 and R02 are external pins of MICRF218. User only needs to connect reference oscillation crystal. See equation (1) and (2) to calculate reference oscillator crystal frequency for either narrow or wide November 2011 bandwidth. Crystal Parameters To operate the MICRF218 with minimum offset, crystal frequencies should be specified with 10pF loading capacitance. Please contact Micrel RF Applications department for crystal parameters. 13 M9999-111111 (408) 944-0800 Micrel MICRF218 Application Information Figure 7. QR218HE1 Application Example, 433.92 MHz, Narrow Band Products application note. The MICRF218 can be fully tested by using one of many evaluation boards designed at Micrel for this device. As simple demonstrator, the QR218HE1 (Figure 7) offers a good start for most applications. It has a helical PCB antenna with its matching network, a bandpass-filter front-end as a pre-selector filter, matching network and the minimum components required to make the device work, which are a crystal, Cagc, and Cth capacitors. The matching network of the helical PCB antenna (C9 and L3) can be removed and a whip antenna (ANT2) or a RF connector (J2) can be used instead. Figure 7 shows the entire schematic of it for 433.92MHz. Other frequencies can be used. Matching network values for other frequencies are listed in the tables below. Capacitor C9 and inductor L3 are the passive elements for the helical PCB matching network. Tight tolerance is recommended for these devices, like 2% for the inductor and 0.1pF for the capacitor. PCB variations may require different component values and optimization. Table 2 shows the matching elements for the device frequency range. For additional information look for Small PCB Antennas for Micrel RF November 2011 Freq (MHz) C9 (pF) L3(nH) 315.0 1.2 75 390.0 1.2 43 418.0 1.2 36 433.92 1.5 30 Table 2. Matching Values for the Helical PCB Antenna If whip antenna is used, remove C9 and place the whip antenna in the hole provided in the PCB. Also, RF signal can be injected there (add RF connector). L1 and C8 form the pass-band-filter front-end. Its purpose is to attenuate undesired outside band noise which reduces the receiver performance. It is calculated by the parallel resonance equation: f 14 1 (2 * L1 * C8) M9999-111111 (408) 944-0800 Micrel MICRF218 Q = SQRT (Rp/50 + 1) Q = 7.06 Xm = Rp / Q Xm = 345.8Ω Resonance Method For L-shape Matching Network: Lc = Xp / (2×Pi×f); Lp = Xm / (2×Pi×f) L2 = (Lc×Lp) / (Lc + Lp); C3 = 1 / (2×Pi×f×Xm) L2 = 38.9nH C3 = 1.06pF Doing the same calculation example with the Smith Chart, it would appear as follows, First, the input impedance of the device is plotted, (Z = 9.54 – j152)Ω @ 433.92MHz.(Figure 8). Table 3 shows the most used frequency values. Freq (MHz) C8 (pF) L1(nH) 315.0 6.8 39 390.0 6.8 24 418.0 6.0 24 433.92 5.6 24 Table 3. Band-Pass-Filter Front-End Values There is no need for the bandpass-filter front-end for applications where it is proven that the outside band noise does not cause a problem. The MICRF218 has image reject mixers which improve significantly the selectivity and rejection of outside band noise. Capacitor C3 and inductor L2 form the L-shape matching network. The capacitor provides additional attenuation for low frequency outside band noise, and the inductor provides additional ESD protection for the antenna pin. Two methods can be used to find these values, which are matched close to 50Ω. One method is done by calculating the values using the equations below, and the other method uses a Smith chart. The latter is made easier by using software that plots the values of the components C8 and L1, like WinSmith by Noble Publishing. To calculate the matching values, one needs to know the input impedance of the device. Table 4 4 shows the input impedance of the MICRF218 and suggested matching values for the most used frequencies. These suggested values may be different if the layout is not exactly the same as the one made here. Freq (MHz) C3 (pF) L2(nH) Z device (Ω) 315.0 1.5 68 16.3 -j210.8 390.0 1.2 47 8.26 – j163.9 418.0 1.2 43 11.1 – j161.9 433.92 1.1 39 9.54 – j152.3 Figure 8. Device’s Input Impedance, Z = 9.54-j152Ω Table 4. Matching values for the most used frequencies Second, the shunt inductor (39nH) and the series capacitor (1.1pF) for the desired input impedance are plotted (Figure 9). One can see the matching leading to the center of the Smith Chart or close to 50Ω. For the frequency of 433.92MHz, the input impedance is Z = 9.54 – j152.3Ω. The matching components are calculated by: Equivalent parallel = B = 1/Z = 0.410 + j6.54 msiemens Rp = 1 / Re (B); Xp = 1 / Im (B) Rp = 2.44kΩ; Xp = 345.8Ω November 2011 15 M9999-111111 (408) 944-0800 Micrel MICRF218 Figure 9. Plotting the Shunt Inductor and Series Capacitor Crystal Y1 may be either SMT or leaded. It is the reference clock for all the device internal circuits. Crystal characteristics of 10pF load capacitance, 30ppm, ESR < 50Ω, -40ºC to +85ºC temperature range are desired. Table 5 shows the crystal frequencies for WB or NB and one of Micrel’s approved crystal manufacturers (www.hib.com.br). REFOSC (MHz) Carrier (MHz) HIB Part Number 9.813135, NB 315 SA-9.813135-F-10-G-30-30-X 12.149596, NB 390.0 SA-12.149596-F-10-G-30-30-X 13.021874, NB 418.0 SA-13.021874-F-10-G-30-30-X 13.517827, NB 433.92 SA-13.517827-F-10-G-30-30-X 9.788232, WB 315 SA-9.788232-F-10-G-30-30-X 12.118764, WB 390.0 SA-12.118764-F-10-G-30-30-X 12.988829, WB 418.0 SA-12.988829-F-10-G-30-30-X 13.483523, WB 433.92 SA-13.483523-F-10-G-30-30-X Table 5. Crystal Frequency and Vendor Part Number November 2011 16 M9999-111111 (408) 944-0800 Micrel MICRF218 The oscillator of the MICRF218 is Colpitts in configuration. It is very sensitive to stray capacitance loads. Thus, very good care must be taken when laying out the printed circuit board. Avoid long traces and ground plane on the top layer close to the REFOSC pins RO1 and RO2. When care is not taken in the layout, and crystals from other vendors are used, the oscillator may take longer times to start as well as the time to good data in the DO pin to show up. In some cases, if the stray capacitance is too high (> 20pF), the oscillator may not start at all. Refer to Equations 1 and 2 for crystal frequency calculations. The local oscillator is low side injection (32 × 13.51783MHz = 432.571MHz), that is, its frequency is below the RF carrier frequency and the image frequency is below the LO frequency. See Figure 10. The product of the incoming RF signal and local oscillator signal will yield the IF frequency, which will be demodulated by the detector of the device. Image Frequency SEL1 JP2 Demod. BW (hertz) Short Short 1625 400 1250 Open Short 3250 200 2500 Short Open 6500 100 5000 Open Open 13000 50 10000 Table 6. JP1 and JP2 setting, 433.92 MHz Other frequencies will have different demodulator bandwidth limits, which are derived from the reference oscillator frequency. Table 7 and 8 below shows the limits for the other two most used frequencies. Desired Signal -fLO Shortest Pulse (µsec) Maximum baud rate for 50% Duty Cycle (hertz) SEL0 JP1 BW (hertz) Shortest Pulse (µsec) Maximum baud rate for 50% Duty Cycle (hertz) Short 1565 416 1204 Open Short 3130 208 2408 Short Open 6261 104 4816 Open Open 12523 52 9633 SEL0 JP1 SEL1 JP2 Short Demod. Table 7. JP1 and JP2 setting, 418.0 MHz f (MHz) Figure 10. Low Side Injection Local Oscillator Narrow and Wide Band Crystal Part Numbers, WB = IF Wide Band, NB = IF Narrow Band JP1 and JP2 are the bandwidth selection for the demodulator bandwidth. To set it correctly, it is necessary to know the shortest pulse width of the encoded data sent in the transmitter. Similar to the example of the data profile in the Figure 11 below, PW2 is shorter than PW1, so PW2 should be used for the demodulator bandwidth calculation which is found by 0.65/shortest pulse width. After this value is found, the setting should be done according to Table 6. For example, if the pulse period is 100µsec, 50% duty cycle, the pulse width will be 50µsec (PW = (100µsec × 50%) / 100). So, a bandwidth of 13kHz would be necessary (0.65 / 50µsec). However, if this data stream had a pulse period with 20% duty cycle, then the bandwidth required would be 32.5kHz (0.65 / 20µsec), which exceeds the maximum bandwidth of the demodulator circuit. If one tries to exceed the maximum bandwidth, the pulse would appear stretched or wider. BW (hertz) Shortest Pulse (µsec) Maximum baud rate for 50% Duty Cycle (Hertz) Short 1460 445 1123 Open Short 2921 223 2246 Short Open 5842 111 4493 Open Open 11684 56 8987 SEL0 JP1 SEL1 JP2 Short Demod. Table 8. JP1 and JP2 setting, 390.0 MHz BW (hertz) Shortest Pulse (µsec) Maximum baud rate for 50% Duty Cycle (Hertz) Short 1180 551 908 Open Short 2360 275 1815 Short Open 4720 138 3631 Open Open 9400 69 7230 SEL0 JP1 SEL1 JP2 Short Demod. Table 9. JP1 and JP2 setting, 315.0 MHz. November 2011 17 M9999-111111 (408) 944-0800 Micrel MICRF218 determine the signal to noise ratio of the RF link, crude range estimate from the transmitter source and AM demodulation, which requires a low Cagc capacitor value. Selection of CTH and CAGC Capacitors Capacitors C6 and C4, Cth and Cagc respectively provide time-based reference for the data pattern received. These capacitors are selected according to data profile, pulse duty cycle, dead time between two received data packets, and if the data pattern has or does not have a preamble. See Figure 11 for an example of a data profile. Shut Down Control The shut down pin (SHDN) is useful to save energy. When its level close to Vdd (SHDN = 1), the device is not in operation. Its DC current consumption is less than 1µA (do not forget to remove R3). When toggling from high to low, there will be a time required for the device to come to steady state mode, and a time for data to show up in the DO pin. This time will be dependent upon many things such as temperature, choice of crystal used, and if the there is an external oscillator with faster startup time. Normally, with the crystal vendors suggested, the data will show up in the DO pin around 1msec time, and 2msec over the temperature range of the device. See Figures 12. PW1 PW2 Preamble Header 1 2 3 4 5 6 7 8 9 10 t1 t2 PW2 = Narrowest pulse width t1 & t2 = data period Figure 11. Example of a Data Profile For best results, the capacitors should always be optimized for the data pattern used. As the baud rate increases, the capacitor values decrease. Table shows suggested values for Manchester Encoded data, 50% duty cycle. SEL0 JP1 SEL1 JP2 Demod. BW (hertz) Cth Cagc (C6) (Cagc) Short Short 1625 100nF 4.7µF Open Short 3250 47nF 2.2µF Short Open 6500 22nF 1µF Open Open 13000 10nF 0.47µF Table 10. Suggested Cth and Cagc Values. Other components used include C5, which is a decoupling capacitor for the Vdd line; R4 reserved for future use and not needed for the evaluation board; R3 for the shutdown pin (SHDN = 0, device is operation), which can be removed if that pin is connected to a microcontroller or an external switch, and R1 and R2 which form a voltage divider for the AGC pin. One can force a voltage in this AGC pin to purposely decrease the device sensitivity. Special care is needed when doing this operation, as an external control of the AGC voltage may vary from lot to lot and may not work the same for several devices. Figure 12. Time-to-Good Data After Shut Down Cycle, Room Temperature DO, RSSI and Shutdown Functions Three other pins are worthy of comment. They are the DO, RSSI, and shut down pins. The DO pin has a driving capability of 0.6mA. This drive current is good enough for most of the logic family ICs in the market today. The RSSI pin provides a transfer function of the RF signal intensity vs. voltage. It is very useful to November 2011 18 M9999-111111 (408) 944-0800 Micrel MICRF218 PCB Considerations and Layout vias. Ground plane must be solid and possibly without interruptions. Avoid ground plane on top next to the matching elements. It normally adds additional stray capacitance which changes the matching. Do not use phenolic material. Use only FR4 or better materials. Phenolic material is conductive above 200MHz. RF path should be as straight as possible avoiding loops and unnecessary turns. Separate ground and Vdd lines from other circuits (microcontroller, etc). Known sources of noise should be laid out as far as possible from the RF circuits. Avoid thick traces, the higher the frequency, the thinner the trace should be in order to minimize losses in the RF path. Figures 14 to 17 show top, bottom and silkscreen layers of printed circuit board for the QR218HE1 board. Gerber files are provided and are downloadable from Micrel Website: www.micrel.com, to fabricate this board. Keep traces as short as possible. Long traces will alter the matching network, and the values suggested will not be valid. Suggested Matching Values may vary due to PCB variations. A PCB trace 100 mills (2.5mm) long has about 1.1nH inductance. Optimization should always be done with exhaustive range tests. Make individual ground connections to the ground plane with a via for each ground connection. Do not share vias with ground connections. Each ground connection = 1 via or more Figure 14. QR218HE1 Top Layer. Figure15. QR218HE1 Bottom Layer, Mirror Image. November 2011 19 M9999-111111 (408) 944-0800 Micrel MICRF218 Figure 16. QR218HE1 Top Silkscreen Layer. Figure 17. QR218HE1 Dimensions. November 2011 20 M9999-111111 (408) 944-0800 Micrel MICRF218 QR218HE1 Bill of Materials, 433.92 MHz Item Part Number Manufacturer ANT1 Description Helical PCB Antenna Pattern ANT2 (np)50-ohm Ant C9 MuRata C4 168mm 20 AWG, rigid wire Qty. 1 0 1.5pF , 0402/0603 1 Murata / Vishay 4.7µF, 0805 1 C3 Murata/Vishay 1.1pF, 0402/0603 C6,C5 Murata / Vishay 0.1µF, 0402/0603 2 C8 Murata 5.6pF, 0402/0603 1 JP1,JP 2, JP3 Vishay short, 0402, 0Ω resistor 2 JP4 (np) not placed 0 J2 (np) not placed 0 J3 CON6 1 L1 Coilcraft / Murata / ACT1 24nH 5%, 0402/0603 1 L2 Coilcraft / Murata / ACT1 39nH 5%, 0402/0603 1 L3 Coilcraft / Murata / ACT1 30nH 2%, 0402/0603 1 (np) 0402, not placed 0 100kΩ 1 R1,R2, R4 R3 Vishay , 0402 Y1 HCM49 www.hib.com.br (np)13.51783MHz Crystal 0 Y1A HC49/US www.hib.com.br 13.51783MHz Crystal 1 U1 MICRF218AYQS Micrel Semiconductor QSOP16 1 Notes: 1. On Semiconductor Tel: 800-344-3860 2. Micro Commercial Corp. Tel: 800-346-3371 3. Sumida Tel: 408-982-9660 4. Murata Tel: 949-916-4000 5. Vishay Tel: 402-644-4218 6. Micrel Semiconductor Tel: 408-944-0800 Table 11. QR218HE1 Bill of Materials, 433.92 MHz, Narrow Band. November 2011 21 M9999-111111 (408) 944-0800 Micrel MICRF218 Package Information QSOP16 Package Type (AQS16) 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. © 2007 Micrel, Incorporated. November 2011 22 M9999-111111 (408) 944-0800 Micrel MICRF218 Revision History Date Edits by: November 2011 Revision Number 23 M9999-111111 (408) 944-0800