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MICRF218
3.3V, QwikRadio 300 MHz to 450 MHz Receiver
(R)
General Description
Micrel's MICRF218 is the world's first integrated ASK / OOK receiver with selectable dual IF bandwidths for 300~450 MHz operation. The receiver architecture is super-heterodyne. The MICRF218 has fully integrated IF section with image rejection to bring performance, simplicity and ease of implementation to the receiver portion of RF actuation. The MICRF218 is a true RF in, data out receiver. IF filter and image rejection functions are built-in. Dual IF bandwidths enable the MICRF218 to capture signals from either high performance or low cost transmitters. In addition, all post-detection data filtering is provided on the MICRF218. The user has a choice of four filter bandwidths that may be selected externally in binary steps, from 1.25 kHz to 10 kHz. The user only needs to program the device with a set of easily determined values, based upon data rate, code modulation format, and desired duty-cycle operation. The MICRF218 has a shutdown control for duty-cycle operation to reduce average current consumption. It has analog RSSI output, indicating the strength of incoming signal. The device is unique for its ability to "escape" from a jamming source and move to an alternate frequency. Dual IF bandwidths function plus fast response time provide easy implementation of dual frequency operations. It can accommodate two reference crystals with the use of an external switch. Once the system detects a strong jamming signal on one frequency, the MICRF218 can switch to another frequency via a switching crystal. This is the ideal receiver for "Jam Avoidance".
Features
* * * * * * * * * * * * * Complete receiver on a chip 300 MHz to 450 MHz frequency range Selectable IF frequency and bandwidth -108 dBm sensitivity, 550kHz IF BW, 1.0 Kbps BER 10 E-2 @ 433.92MHz -106 dBm sensitivity, 1500kHz IF BW, 1.0 Kbps BER 10 E-2 @ 433.92MHz Built-in Image Rejection Mixer Low Power, 4 mA @ 315 MHz, continuous on Data Rates to 10 kbps (Manchester Encoded) @ 433.92 MHz Duty Cycling Capable > 100:1 (shut down mode) Analog RSSI Output No IF filter required Excellent selectivity and noise rejection Low external part count
Ordering Information
Part Number MICRF218AYQS Temperature Range -40 to +85C Package 16-Pin QSOP
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
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MICRF218
Application Example
Y1 9.8131MHz ANT PCB Pattern
1
C2 1.5pF 50V
2 3 4
+3V L1 39nH C1 6.8pF L2 68nH C3 0.1F 16V
5 6 7 8
U1 MICRF218AYQS RO1 RO2 GNDRF NC ANT RSSI GNDRF CAGC VDD CTH IF_BW SEL1 SEL0 DO SHDN GND
16 15 14 13 12 11 10 9
RSSI
DO
C4 0.1F 16V
C5 4.7F 6.3V
IF_BW CONTROL
315MHz/315.802, 900Hz Baud Rate Example
Pin Configuration
RO1 GNDRF ANT GNDRF Vdd IF_BW SEL0 SHDN
1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9
RO2 NC RSSI CAGC CTH SEL1 DO GND
MICRF218AYQS
Pin Description
16-Pin QSOP 1 2 3 4 5 6 7 8 9 Pin Name RO1 GNDRF ANT GNDRF VDD IF_BW SEL0 SHDN GND 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. 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) Shutdown logic control input. Active internal pull-up and must be pulled low for Normal Operation. Negative supply connection for all chip functions except RF input.
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16-Pin QSOP 10 11 Pin Name DO SEL1
MICRF218
Pin Function Demodulated data output. 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) 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. AGC filter capacitor. A capacitor, normally greater than 0.47uF, is connected from this pin to GND Received signal strength indication output. Output is from a buffer with 200 ohms typical output impedance. 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.
12 13 14 15 16
CTH CAGC RSSI NC RO2
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Absolute Maximum Ratings(1)
Supply Voltage (VDD) ................................................ +5V Input Voltage............................................................. +5V Junction Temperature..........................................+150C Lead Temperature (soldering, 10sec.) ..................260C Storage Temperature (TS) .................... -65C to +150C Maximum Receiver Input Power........................ +10dBm ESD Rating(3) .......................................................... 3KV
Operating Ratings(2)
Supply voltage (VDD) ............................ +3.0V to +3.6V Ambient Temperature (TA) .................. -40C to +85C 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 -40C - TA +85C. Symbol Parameter Condition Min Typ Max Units Continuous Operation, fRX = 315 MHz 4.0 mA IDD MICRF218 Operating Supply Current 20:1 Duty Cycle, fRX = 315 MHz Continuous Operation, fRX = 433.92 MHz 20:1 Duty Cycle, fRX = 433.92 MHz Ishut Shut down Current Image Rejection 1 IF Center Frequency 1 IF Center Frequency Receiver Sensitivity @ 1kbps Receiver Sensitivity @ 1kbps
st st
0.2 5.5 0.3 1 20
mA mA mA A dB MHz MHz MHz MHz dBm dBm dBm dBm kHz kHz kHz kHz 80 %
RF/IF Section fRX = 315 MHz, Narrow IF fRX = 433.92 MHz, Narrow IF fRX = 315 MHz, Wide IF fRX = 433.92 MHz, Wide IF fRX = 315 MHz, Narrow IF (50 ohms) fRX = 433.92 MHz, Narrow IF (50 ohms) fRX = 315 MHz, Wide IF (50 ohms) fRX = 433.92 MHz, Wide IF (50 ohms) fRX = 315 MHz, Narrow IF fRX = 433.92 MHz, Narrow IF fRX = 315 MHz, Wide IF fRX = 433.92 MHz, Wide IF fRX = 315 MHz fRX = 433.92 MHz Note 6 20 0.98 1.4 1.8 2.4 -108 -108 -106 -106 400 550 1000 1500 16-j211 9.54-j152
IF Bandwidth
Antenna Input Impedance Receive Modulation Duty Cycle
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MICRF218
Symbol
Parameter AGC Attack / Decay Ratio AGC pin leakage current AGC Dynamic Range @ fRX = 433.92MHz
Condition tATTACK / tDECAY TA = 25C TA = +85C RFIN @ -50dBm RFIN @ -110dBm 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
Min
Typ 0.1 2 800 1.13 1.70
Max
Units
nA nA V V
Reference Oscillator 9.8131 9.78823 13.5178 13.48352 300 0.2 V(REFOSC) = 0V 3.5 1.5 MHz MHz MHz MHz k Vp-p A
Frequency
Input Impedance 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
fREFOSC = 9.8131MHz, 315MHz, Note 8 TA = 25C TA = +85C SEL0=0, SEL1=0 SEL0=0, SEL1=1 SEL0=1, SEL1=0 SEL0=1, SEL1=1 fREFOSC = MHz, 433.92MHz, note 8 TA = 25C TA = +85C SEL0=0, SEL1=0 SEL0=0, SEL1=1 SEL0=1, SEL1=0 SEL0=1, SEL1=1
165 2 800 1180 2360 4720 9420 120 2 800 1625 3250 6500 13000
k nA Hz Hz Hz Hz k nA Hz Hz Hz Hz
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MICRF218
Symbol
Parameter Input High Voltage Input Low Voltage DO pin output current Output rise and fall times
Condition Pins DO (As input), SHDN Pins DO (As input), SHDN Source @ 0.8 Vdd Sink @ 0.2 Vdd CI = 15 pF, pin DO, 10-90%
Min
0.8VDD
Typ
Max
Units V
Digital / Control Functions
0.2VDD
V A sec
260 600 2 0.22 to 2
RSSI RSSI DC Output Voltage Range RSSI response slope RSSI Output Current RSSI Output Impedance RSSI Response Time
Notes: 1. 2. 3. 4. Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Device are ESD sensitive. Use appropriate ESD precaution. Exceeding the absolute maximum rating may damage the device. 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 . 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. 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) x bit time, and TOFF = TBURST - TON.) 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 ) x ( 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 ) x ( parameter at FTABMHz )
V mV/ dBm mA Sec
-90 dBm to -40 dBm
35 1.5 200
50% data duty cycle, input power to Antenna = -20 dBm
0.3
5. 6.
7.
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MICRF218
Typical Characteristics
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LO Leakage in RF Port
Re-radiation from MICRF218 Antenna Port
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MICRF218
UHF Downconverter
IMAGE REJECT FILTER fc
CAGC AGC
ANT
RF Amp
IF Amp mixer
Detector RSSI RSSI
VDD
-f i
f
CONTROL LOGIC
VSS
fLO
mixer IF_BW Wide / Narrow
Programmable Low Pass Filter
OOK Demodulator
SLICER
SEL0 SEL1 IF_BW SHDN
SYNTHESIZER CONTROL LOGIC
DO
DO
Reference and Control
REFERENCE OSCILLATOR
CONTROL LOGIC
Slicing Level
CTH
RO1
Crystal
RO2
Figure 1 Simplified Block Diagram
Functional Description
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.
Receiver Operation
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 the image reject filter where they are combined to reject the image frequencies. The IF signal then
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MICRF218
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:
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.
Dual Frequency Configuration Examples: Scenario 1:
Operating Freq (1) MHz 2.178 (32 + ) 12 The crystal frequency for Narrow Bandwidth IF operation is given by: REFOSC = Operating Freq (2) MHz 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 =
* 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.
Scenario 2:
IF_Parameter = IF_Parameter @ 433.92 MHz Operating Freq (MHz) * 433.92(MHz)
(3)
* 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.
Scenario 3:
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 frequency may use the wider IF bandwidth by utilizing
* 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.
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J4 IF BANDWIDTH CONTROL 1 2 CON2 VDD = WIDE BANDWIDTH 0V = NARROW BANDWIDTH +3V U1 MICRF218AYQS RO1 RO2 GNDRF NC ANT RSSI GNDRF CAGC VDD CTH IF_BW SEL1 SEL0 DO SHDN GND JPR1 0 OHMS
16 15 14 13 12 11 10 9
MICRF218
J1 1 EXTERNAL REFERENCE OSCILLATOR INPUT 2 REFOSC C1 NP
JPR2 NP R1 NP
Y1 9.8131MHz
Y2 12.1287MHz
1
J2 RF IN
L4 100nH
C2 2.2pF
L3 100nH
2 3 4
TSDF1220W Q1 R2 NP C4 0.047F C5 4.7F R7 100k
TSDF1220W Q2
+3V C3 33pF L2 3.9nH C5 100nF
5 6 7 8
R11 100k
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 J3 3.0 to 3.3V 3.0 to 3.3V COM SHDN DO REF-OSC CNTR COM 1 2 3 4 5 6 7
R3 NP +3V L3 ZCB-0603
R5 100K
C7 NP
R4 0 OHMS R8 10k R10 100k
R6 10k R9 10k
+3V DATA OUT
NP = Not Placed
Figure 4. Dual Frequency QR218BP_SWREF, 315 MHz and 390 MHz
Figure 5 Evaluation Board
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MICRF218
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. 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 1.5A current is sourced into the external CAGC capacitor. When the output signal is greater than 750mV, a 15A 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. 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
Single Crystal Operation for Dual Frequency Operation
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) (384 + 2.178) (5) (384 - 1.198)
Freq2 Wide Bandwidth = Freq1 Narrow Bandwidth *
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
(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 0 1 0 1 SEL1 0 0 1 Demod BW (@ 434MHz) 1625Hz 3250Hz 6500Hz Figure 6. Reference Oscillator Circuit
1 13000Hz - default Table 1. Demodulation BW Selection
The reference oscillator in the MICRF218 (Figure 6) uses a basic Colpitts crystal oscillator configuration
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MICRF218
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.
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MICRF218
Application Information
Figure 7. QR218HE1 Application Example, 433.92 MHz, Narrow Band
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 September 2007 15
Products application note.
Freq (MHz) 315.0 390.0 418.0 433.92 C9 (pF) 1.2 1.2 1.2 1.5 L3(nH) 75 43 36 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= 1 (2 * L1 * C8)
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Freq (MHz) 315.0 390.0 418.0 433.92 C8 (pF) 6.8 6.8 6.0 5.6 L1(nH) 39 24 24 24
MICRF218 Q = SQRT (Rp/50 + 1) Q = 7.06 Xm = Rp / Q Xm = 345.8 Resonance Method For L-shape Matching Network: Lc = Xp / (2xPixf); Lp = Xm / (2xPixf) L2 = (LcxLp) / (Lc + Lp); C3 = 1 / (2xPixfxXm) 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) @ 433.92MHz.(Figure 8).
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 50. 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 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) 315.0 390.0 418.0 433.92 C3 (pF) 1.5 1.2 1.2 1.1 L2(nH) 68 47 43 39 Z device () 16.3 -j210.8 8.26 - j163.9 11.1 - j161.9 9.54 - j152.3
Figure 8. Device's Input Impedance, Z = 9.54-j152 Table 4. Matching values for the most used frequencies
For the frequency of 433.92MHz, the input impedance is Z = 9.54 - j152.3. 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 = 2.44k; Xp = 345.8
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 50.
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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 < 50, -40C to +85C 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) 9.813135, NB 12.149596, NB 13.021874, NB 13.517827, NB 9.788232, WB 12.118764, WB 12.988829, WB 13.483523, WB
Carrier (MHz) 315 390.0 418.0 433.92 315 390.0 418.0 433.92
HIB Part Number SA-9.813135-F-10-G-30-30-X SA-12.149596-F-10-G-30-30-X SA-13.021874-F-10-G-30-30-X SA-13.517827-F-10-G-30-30-X SA-9.788232-F-10-G-30-30-X SA-12.118764-F-10-G-30-30-X SA-12.988829-F-10-G-30-30-X SA-13.483523-F-10-G-30-30-X
Table 5. Crystal Frequency and Vendor Part Number
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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 x 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.
SEL0 JP1
SEL1 JP2
Demod. BW (hertz) 1625 3250 6500 13000
Shortest Pulse (sec) 400 200 100 50
Maximum baud rate for 50% Duty Cycle (hertz) 1250 2500 5000 10000
Short Open Short Open
Short Short Open Open
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.
SEL0 JP1 SEL1 JP2 Demod. BW (hertz) 1565 3130 6261 12523 Shortest Pulse (sec) 416 208 104 52 Maximum baud rate for 50% Duty Cycle (hertz) 1204 2408 4816 9633
Short Open Short Open
Short Short Open Open
Table 7. JP1 and JP2 setting, 418.0 MHz Figure 10. Low Side Injection Local Oscillator SEL0 JP1 SEL1 JP2 Demod. BW (hertz) 1460 2921 5842 11684 Shortest Pulse (sec) 445 223 111 56 Maximum baud rate for 50% Duty Cycle (Hertz) 1123 2246 4493 8987
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 100sec, 50% duty cycle, the pulse width will be 50sec (PW = (100sec x 50%) / 100). So, a bandwidth of 13kHz would be necessary (0.65 / 50sec). However, if this data stream had a pulse period with 20% duty cycle, then the bandwidth required would be 32.5kHz (0.65 / 20sec), which exceeds the maximum bandwidth of the demodulator circuit. If one tries to exceed the maximum bandwidth, the pulse would appear stretched or wider.
Short Open Short Open
Short Short Open Open
Table 8. JP1 and JP2 setting, 390.0 MHz SEL0 JP1 SEL1 JP2 Demod. BW (hertz) 1180 2360 4720 9400 Shortest Pulse (sec) 551 275 138 69 Maximum baud rate for 50% Duty Cycle (Hertz) 908 1815 3631 7230
Short Open Short Open
Short Short Open Open
Table 9. JP1 and JP2 setting, 315.0 MHz.
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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.
PW1 PW2 Preamble Header 1 2 3 4 5 6 7 8 9 10 t1 t2 PW2 = Narrowest pulse width t1 & t2 = data period
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.
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 1A (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.
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 Short Open Short Open SEL1 JP2 Short Short Open Open Demod. BW (hertz) 1625 3250 6500 13000 Cth (C6) 100nF 47nF 22nF 10nF Cagc (Cagc) 4.7F 2.2F 1F 0.47F
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.
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
Figure 12. Time-to-Good Data After Shut Down Cycle, Room Temperature
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MICRF218
PCB Considerations and Layout
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 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.
Figure 14. QR218HE1 Top Layer.
Figure15. QR218HE1 Bottom Layer, Mirror Image.
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MICRF218
Figure 16. QR218HE1 Top Silkscreen Layer.
Figure 17. QR218HE1 Dimensions.
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MICRF218
QR218HE1 Bill of Materials, 433.92 MHz
Item ANT1 ANT2 C9 C4 C3 C6,C5 C8 JP1,JP 2, JP3 JP4 J2 J3 L1 L2 L3 R1,R2, R4 R3 Y1 Y1A U1
Notes: 1. 2. 3. 4. 5. 6. On Semiconductor Tel: 800-344-3860 Micro Commercial Corp. Tel: 800-346-3371 Sumida Tel: 408-982-9660 Murata Tel: 949-916-4000 Vishay Tel: 402-644-4218 Micrel Semiconductor Tel: 408-944-0800
Part Number
Manufacturer (np)50-ohm Ant MuRata Murata / Vishay Murata/Vishay Murata / Vishay Murata Vishay 4.7F, 0805 1.1pF, 0402/0603 0.1F, 0402/0603 5.6pF, 0402/0603 short, 0402, 0 resistor (np) not placed (np) not placed CON6 Coilcraft / Murata / ACT1 Coilcraft / Murata / ACT1 Coilcraft / Murata / ACT1 24nH 5%, 0402/0603 39nH 5%, 0402/0603 30nH 2%, 0402/0603 (np) 0402, not placed Vishay 100k , 0402
Description Helical PCB Antenna Pattern 168mm 20 AWG, rigid wire 1.5pF , 0402/0603
Qty. 1 0 1 1 2 1 2 0 0 1 1 1 1 0 1 0 1 1
HCM49 HC49/US MICRF218AYQS
www.hib.com.br www.hib.com.br Micrel Semiconductor
(np)13.51783MHz Crystal 13.51783MHz Crystal QSOP16
Table 11. QR218HE1 Bill of Materials, 433.92 MHz, Narrow Band.
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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. (c) 2007 Micrel, Incorporated.
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Revision History Date Edits by:
Revision Number
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