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MICRF221
3.3V, QwikRadio(R) 850 MHz to 950 MHz Receiver
General Description
The MICRF221 is a third generation QwikRadio receiver, offering all the benefits of Micrel's earlier QwikRadio(R) products with significant improvements, including: enhanced sensitivity, automatic duty-cycle feature and RSSI output. The MICRF221, Figure 1, is a super-heterodyne receiver, designed for OOK and ASK modulation. The down-conversion mixer also provides image rejection. The MICRF221 receiver provides a SLEEP Mode for duty-cycle operation and an enhanced, customer programmable "WAKE" function. These features are further combined into a wholly integrated "self-polling" scheme that is ideal for low and ultra-low power applications, such as RKE and RFID All post-detection data filtering is provided on the MICRF221 receiver. Any one of four filter bandwidths may be selected externally by the user in binary steps, from 1.25 kHz to 10 kHz. The user needs only to program the device with a set of easily determined values based on data rate, code modulation format, and desired duty-cycle operation.
(R)
Features
* * * * * * * * * * * * * Complete Receiver on a Chip -109dBm sensitivity, 1 kbps and BER 10E-02 Image Rejection Mixer 850 MHz to 950 MHz frequency range Low Power, 9mA @ 868 MHz, continuous on Data Rates to 10kbps (Manchester Encoded) Auto polling (sleep mode, current < 0.1 mA) Analog RSSI Output Programmable "Low Sensitivity" mode No IF filter required Excellent selectivity and noise rejection Low external part count Additional Functions Programmed through serial interface
Ordering Information
Part Number MICRF221AYQS Temperature Range -40 to +105C Package 16-Pin QSOP
Typical Application
Figure 1: MICRF221 Receiver 915.0 MHz, 1kHz Baud Rate Example
QwikRadio is a registered trademark of Micrel, 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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MICRF221
Pin Configuration
RO1 GNDRF ANT GNDRF Vdd SQ SEL0 SHDN 1 2 3 4 5 6 7 8 16 RO2 15 SCLK 14 RSSI 13 CAGC 12 CTH 11 SEL1 10 DO 9 GND
Figure 2. MICRF221AYQS Pin Configuration
Pin Description
16-Pin QSOP 1 Pin Name RO1 Pin Function Reference Oscillator (input): Reference resonator input connection to pierce oscillator stage. May also be driven by external reference signal of 1.5V p-p amplitude maximum. 7pF to GND during normal operation. Negative supply connection associated with ANT RF input. Antenna (input): RF signal input from antenna. Internally AC coupled. It is recommended a matching network with an inductor-to-RF ground be used to improve ESD protection. Negative supply connection associated with ANT RF input. Positive supply connection for all chip functions. Squelch control logic input with an active internal pull-up when not shut down. Low to reverse level set by serial interface bit D17. Low enables squelch for default SIF register. Select (input): Logic control input with active 3A (8A max) internal pull-up when not in shutdown or SLEEP mode. It does not need to be defined in SLEEP mode. Used in conjunction with SEL1 to control D3 bandwidth LSB when serial interface contains default setting. Shutdown logic control input. Active internal pull-up. Negative supply connection for all chip functions except for RF input. Demodulated data (output): May be blanked until bit checking test is acceptable. A current limited CMOS output during normal operation this pin is also used as a CMOS Schmitt input for serial interface data. A 25k pull-down is present when device is in shutdown and sleep modes. Select (input): Logic control input with active 3A (8A max) internal pull-up when not in shutdown or SLEEP mode. It does not need to be defined in SLEEP mode. Used in conjunction with SEL0, to control D4 bandwidth MSB, when serial interface contains default setting. 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 0.47F, is connected from this pin-to-GND Received signal strength indication (output): Output is from a switched capacitor integrating op amp with 220 typical output impedance. Serial interface input clock. CMOS Schmitt input. A 25k pull-down is present when device is in shutdown mode. Reference resonator connection. 7pF to GND during normal operation.
2 3 4 5 6 7
GNDRF ANT GNDRF Vdd SQ SEL0
8 9 10
SHDN GND DO
11
SEL1
12
CTH
13 14 15 16
CAGC RSSI SCLK RO2
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Absolute Maximum Ratings(1)
Supply Voltage (Vdd) ................................................. +5V Input Voltage. ............................................................. +5V Junction Temperature ...........................................+150C Lead Temperature (soldering, 10sec.) ....................300C Storage Temperature (Ts)...................... -65C to +150C Maximum Receiver Input Power ......................... +10dBm EDS Rating(3) .....................................................2KV HBM
Operating Ratings(2)
Supply voltage (Vdd)............................. +3.0V to +3.6V Ambient Temperature (TA) ................. -40C to +105C Input Voltage (Vin) ................................................. 3.6V Maximum Input RF Power................................. -20dBm Receive Modulation Duty Cycle(6) .................... 20~80%
Electrical Characteristics
Specifications apply for VDD=3.3V, VSS = 0V, CAGC = 4.7uF, CTH = 0.1uF, fRX = 850 MHz to 950 MHz unless otherwise noted. Bold values indicate -40C - TA - 105C.
Symbol Iss
Parameter MICRF221 Operating Supply Current Shut down Current
Condition Continuous Operation, fRX = 868 MHz Continuous Operation, fRX = 915 MHz
Min
Typ 9.0 9.5 50
Max
Units mA nA
Ishut
RF/IF Section
Symbol
Parameter Image Rejection 1st IF Center Frequency
Condition
Min
Typ 20
Max
Units dB MHz
fRX = 868 MHz fRX = 915 MHz
1.219 1.285 -109 -109 360 380 9.4 - j72 9 - j67 20 -78 0.1 +/-2 +/-800 80
Receiver Sensitivity @ 1kbps(4) IF Bandwidth
fRX = 868 MHz (matched to 50) fRX = 915 MHz (matched to 50) fRX = 868 MHz fRX = 915 MHz
dBm
kHz
Antenna Input Impedance Receive Modulation Duty Cycle Spurious Reverse Isolation(5) AGC Attack / Decay Ratio AGC pin leakage current
fRX = 868 MHz fRX = 915 MHz Note 6 ANT pin, RSC = 50 tATTACK / tDECAY TA = 25C TA = +105C
% dBm
nA
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Electrical Characteristics (continued)
Reference Oscillator
Symbol
Parameter Reference Oscillator Frequency Reference Oscillator Input Impedance Time to Data Reference Oscillator Input Range Reference Oscillator Source Current
Condition fRX = 868 MHz fRX = 915 MHz RO1 Pin From Shut Down With External Drive RO1 Pin, V(REFOSC) = 0V
Min
Typ 13.54856 14.27643 1500 1
Max
Units MHz
k msec 1.5 Vp-p A
0.5 380
Autopolling Operation
(7)
Symbol
Parameter Tsleep Programming Range
Condition
Min 10
Typ
Max 1300
Units msec A
Isleep(8)
SLEEP Current
2msec on, 1.3 sec Off
15
Demodulator
Symbol
Parameter CTH Source Impedance CTH Leakage Current
Condition Frefosc = 14.27643MHz TA = 25C TA = +105C
Min
Typ 100 +/-2 +/-800
Max
Units k nA
Demodulator Filter Bandwidth @ 915MHz
Digital / Control Functions
Programmable, see application section
1712
13000
Hz
Symbol
Parameter Input High Voltage Input Low Voltage Output Voltage High Output Voltage Low DO pin output current
Condition Pins SCLK, DO (As input), SHDN Pins SCLK, DO (As input), SHDN DO DO As output, source @ 0.8 VDD As output, sink @ 0.2 VDD
Min 0.8Vdd
Typ
Max
Units V
0.2Vdd 0.8Vdd 0.2Vdd 260 600 2
V V V A sec
Output rise and fall times
CI = 15 pF, pin DO, 10-90%
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Electrical Characteristics (continued)
RSSI
Symbol
Parameter RSSI DC Output Voltage Range RSSI response slope RSSI Output Impedance
Condition
Min
Typ 0.2 to 2.0
Max
Units V mV/dB
-109 dBm to -40 dBm
26 220
Notes: 1. 2. 3. 4. 5. 6. Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Device is ESD sensitive. Use appropriate ESD precautions. 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). Spurious reverse isolation represents the spurious component which appears on the RF input pin (ANT), measured into 50Ohms with an input RF matching network. When data burst does not contain preamble, duty cycle is 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 isTON/(TON + TOFF)= 50%; without preamble, duty cycle is TON/(TON + TOFF + TQUIET) = 50msec/200msec = 25%. TON is the number of 1's during the burst time x bit time TOFF = TBURST - TON. Auto-polling refers to power-cycling mode of operation where characteristics of the received signal are used to determine the likelihood of an incoming data signal at the beginning of the Ton period. If there is no signal detected within a period programmable by the user, the user can program the number of bits: 0,2,4,8 that must be good for device to wake up. The time will depend on the data rate. If two bad bits are detected this will cause device to revert to SLEEP. If no bits are detected device will revert to SLEEP in 5ms, 10ms, or 20ms depending on selected demodulator bandwidth. Otherwise, the device remains "On" until commanded into SLEEP by an external source e.g., decoder or microprocessor. This technique minimizes the average Ton time. Refer to Serial Interface and Applications sub-sections for further details. Average SLEEP mode current depends on the SLEEP time programmed and the SLEEP oscillator variation which is ~+/-20% independent of ref osc.
7.
8.
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Typical Characteristics
Sensitivity Graphs
DC Current vs. Frequency
NORMALIZED SENSITIVITY (dB) 0.0 -10.0 -20.0 -30.0 -40.0 -50.0 -60.0 898 903 908 913 918 923 928 933
12.0 DC CURRENT (mA) 11.0 10.0 9.0 8.0 7.0 6.0 650
Selectivity vs. Frequency Response
750 850 950 FREQUENCY (MHz)
1050
FREQUENCY (MHz)
2.0 1.9 VOLTAGE (V) 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 -130
AGC Voltage vs. Input Power
-80 -30 POWER (dBm)
20
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Functional Diagram
UHF DOWNCOVERTER MIXER
CAGC CONTROL LOGIC DESENSE AGC CONTROL
LNA MIXER
-f
f
IF AMP
DETECTOR
RSSI
RSSI
i fLO IMAGE REJECT FILTER CONTROL LOGIC PROGRAMMABLE FILTER OOK DEMODULATOR
SYNTHESIZER
SLICER
SLEEP OSCILLATOR
SLEEP TIMER
BITCHECK WAKE-UP SQUELCH
DO' DO CTH
AUTOPOLL
DO' DO REFERENCE OSCILLATOR
CONTROL LOGIC CONTROL LOGIC
SLICE LEVEL
REFERENCE AND CONTROL
Figure 3. Simplified Block Diagram
Functional Description
The simplified block diagram, shown in Figure 3, illustrates the basic structure of the MICRF221 receiver. It is made of four sub-blocks: * * * * UHF Down-converter OOK Demodulator Reference and Control logic Auto-poll circuitry.
pre-selector band-pass filter.
Receiver Operation
UHF Downconverter The UHF down-converter has six components: LNA, mixers, synthesizer, image reject filter, band pass filter and IF amp. 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 amplifier. The amplified RF signal is then fed to the RF ports of two double balanced mixers.
Outside the device, the MICRF221 receiver requires just three components to operate: two capacitors (CTH, and CAGC) and the reference frequency device (usually a quartz crystal). An additional five components are used to improve performance: a power supply decoupling capacitor, two components for the matching network, and two components for the October 2008 7
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Mixers and Synthesizer The LO port of the mixers are driven by quadrature local oscillators of the synthesizer block. The synthesizer block produces the local oscillator signal on the low side of the desired RF signal with suppression of the image frequency, at twice the IF frequency below the wanted signal. The local oscillator is set to 64 times the crystal reference frequency by way of a phase locked loop synthesizer with a fully integrated loop filter. Image Reject Filter and Band-Pass Filter The IF ports of the mixer produce quadrature downconverted IF signals. The IF signal is filtered by the image reject filter to remove image frequency components and then follow up with a third order band-pass filter. The IF center frequency is 1.285MHz. The IF BW is 380kHz @ 915 MHz, and the IF BW varies with RF operating frequency. The IF BW can be calculated via direct scaling. BW IF = BW IF@ 915MHz*(Operating Freq (MHz)/ 915) These filters are fully integrated inside the MICRF221. After filtering, four active gain controlled amplifier stages enhance the IF signal to proper level for demodulation. OOK Demodulator The demodulator section is comprised of detector, programmable low pass filter, slicer, AGC and Desense. 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. There are four settings for programmable low-pass filter BW options: 1625Hz, 3250Hz, 6500Hz, 13000Hz. for 915MHz operation. Low pass filter BW will vary with RF Operating Frequency. Filter BW values can easily calculated by direct scaling. See equation below for filter BW calculation: BW Operating Freq = BW @ 915MHz*(Operating Freq (MHz)/ 915) It is very important to choose filter setting that fits best for the intended data rate to minimize data distortion. Demod BW is set at 13000Hz @ 915MHz as default (assuming both SEL0 and SEL1 pins are floating). The low pass filter can be hardware set by external pins SEL0 and SEL1, or via serial programming through register D3 and D4 October 2008 8
D3 SEL0 0 1 0 1
D4 SEL1 0 0 1 1
Demod BW (@ 915MHz) 1625Hz 3250Hz 6500Hz 13000Hz - default
Slicer and Slicing Level The signal prior to the slicer is still AM. The data slicer converts the AM signal into ones and zeros based upon the threshold voltage built up in the CTH capacitor. After the slicer, the signal is ASK or OOK digital data. The slicing threshold defaults at 50%. The slicing threshold can be set via serial programming through register D5 and D6.
D5 1 0 1 0 D6 0 1 1 0 Slicing Level Slice Level 30% Slice Level 40% Slice Level 50% Slice Level 60%
- default
AGC AGC monitors the signal amplitude from the output of the programmable low-pass filter. When the output signal is less than 750mV thresh-hold, AGC increases the gain of the mixer and the IF amplifier. When the output signal is greater than 750mV, the AGC lowers the gain of the mixer and the IF amplifier. Desense Desense is a function designed to reduce the sensitivity of the MICRF221 receiver to a maximum of 45dB for training the MICRF221 receiver to recognize an intended transmitter. Very often, a receiver needs to learn how to recognize a particular transmitter. It is important for the receiver not to learn the signal of a stray transmitter near by. The simplest solution is to turn down the receiver gain, so the receiver only recognizes the transmitter at close range. The desense function is accessible only through serial programming.
M9999-100108 (408) 955-1690
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MICRF221 The reference oscillator in the MICRF221 uses a basic Pierce crystal oscillator configuration with MOS transconductor to provide negative resistance. MICRF221 has built-in load capacitors for the crystal oscillator, shown in Figure 4, even though external load capacitors are still needed for tuning to the right frequency. RO1 and RO2 are external pins of the MICRF221 and are to connect to the reference oscillator crystal. The reference oscillator crystal frequency can be calculated as follows: FREF OSC = FRF/(64 + 1.1/12) For 868.35 MHz, FREF OSC = 13.54856 MHz
R V BIAS
D0
D1
D2
MODE: Desense
0 1 1 1 1
X 0 1 0 1
X 0 0 1 1
No Desense - default 7dB Desense 19dB Desense 32dB Desense 42dB Desense
Reference Control There are two components in the Reference and Control sub-block: 1) Reference Oscillator and 2) Control Logic, Serial Interface and Parallel Inputs. Reference Oscillator
RO2 C
For 915 MHz FREF OSC = 14.27643 MHz To operate the MICRF221 with minimum offset, crystal frequencies should be specified with 10pF loading capacitance.
RO1 C
Figure 4. MICRF221 Reference Oscillator Circuit
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SQUELCH Decode Data Edge Pulses CLK DOUT CLK Edge Detector CLK Window Counter D 8 Stage Shift Register >=7 Good R <=4 Good S Q
MICRF221
SQUELCH Disables DO
Window Decode
Decode Bad Bits Good Bit QA1 Bad Bit Returns to SLEEP
Decode Good Bit Count
CLK WATCHDOG Timer Auto Poll S Serial Control Register R
D7 D8 Select 0, 2, 4, 8 Good Bits Before Wakeup WAKEUP Timer (300s) D15 = 0 for Normal Operation D15 = 1 for Auto Polled Operation
D15
Figure 4. MICRF221 Autopoll-Bitcheck-Block Diagram
Auto-Polling
The auto-poll block (Figure 4) contains a low power oscillator to drive the sleep timer when the rest of the device is powered down, plus circuits to check whether the received bits are good. Auto-polling is controlled by bit D15 in the serial register, in conjunction with bits D12,13,14 to set the sleep timer period. Bits D7, D8, are used for control of the bitchecking operation and bits D9, D10, D11 are used to adjust the sensitivity of the bitcheck action. For simple auto-polling without bitchecking, send a serial command with bit 15 set high and bits D12, D13, D14 set to the desired sleep time. The device will go to sleep for the programmed timer duration then wake up to receive data if present. Device will stay awake until serial bit D15 is set low then set high again to enable a further sleep period. Sleep duty cycle may be controlled by the timing of serial commands. For polling with bitchecking the serial register bits D7and D8 need to be set for the number of bits to be checked as good, before the receiver outputs data at the DO pin. The bitcheck window bits D9, D10, D11 must also be set to match the data period. The default shortest window time gives the least critical bitcheck action. For better discrimination, the window setting may be increased up towards the normal minimum time expected between data edges. Note that a window time set longer than this will result in all bits being tested as bad and the device will remain in sleep polling mode. Now when the serial command is sent to set bit D15 high the device will go to sleep for the timer period, then will start to receive and check bits. The device will output data again at DO as soon as the programmed number of good RTZ bits have been received. If a bad bit is seen the device will return to sleep mode and poll again for good data after the timeout period. Both high and low periods are checked for each RTZ bit. If data transitions are not received the device will return to sleep after the bitcheck watchdog timeout period unless bit D18 has been sent, in which case the device will continue to check bits until sufficient good bits enable the device to wake up, or bad bits return the device to sleep.
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D9 0 1 0 1 0 1 0 1 D10 0 0 1 1 0 0 1 1 D11 0 0 0 0 1 1 1 1
MICRF221
MODE: Bitcheck Window Times (915MHz) 67us, 136us, 270us, 541us 64us, 126us, 252us, 505us 59us, 118us, 234us, 469us 54us, 108us, 216us, 434us 49us, 100us, 198us, 397us 45us, 90us, 180us, 361us 41us, 82us, 163us, 325us 36us, 72us, 144us, 289us
Operation Trigger pulses are generated from internal D0 edges and compare with programmable window generated from the reference clock frequency. If time between data edges falls within the window data pulse width is bad. Detected stable bits are counted. Wakeup will occur allowing data to output if sufficient data bits are detected. Two bad pulses or lack of pulse cause device to go to sleep for sleep timer duration. Squelch action During normal operation, if 4 or less out of 8 bit pulses are good squelch output is actived. If good bit count increases to 7 or more in any 8 sequential bits squelch output is set low allowing data to output at DO pin.
D12 0 1 0 1 0 1 0 1 D15 0 1 D16 0 1 D17 0 1 D18 0
D13 0 0 1 1 0 0 1 1
D14 0 0 0 0 1 1 1 1
Serial Interface
Control Register Individual Truth Tables:
D0 0 1 1 1 1 D3 0 1 0 1 D5 1 0 1 0 D7 0 1 0 1 D1 X 0 1 0 1 D4 0 0 1 1 D6 0 1 1 0 D8 0 0 1 1 D2 X 0 0 1 1 MODE: Desense No Desense - default 7dB Desense 19dB Desense 32dB Desense 42dB Desense
MODE: Sleep Time 10ms 20ms 40ms 80ms 160ms 320ms 640ms 1280ms
MODE: Auto Poll Awake - does not poll - default Auto-polls with Sleep periods MODE: Demod BW Select Normal Demod BW's - default Fast Demod BW's MODE: Squelch Enable Squelch circuit off - default Squelch circuit active MODE Sleep polling watchdog active - default Watchdog time for D3, D4, BW setting: 11 01 10 00 5ms 5ms 10ms 20ms Sleep polling watchdog disabled - unlimited poll period MODE RSSI offset 0mV - default RSSI offset +200mV
MODE: Demod Bandwidth (at 915MHz) 1625Hz 3250Hz 6500Hz 13000Hz - default MODE Slice Level 30% Slice Level 40% Slice Level 50% Slice Level 60%
- default
MODE: Bit Check Setting Bitcheck 0 bits - default Bitcheck 2 bits Bitcheck 4 bits Bitcheck 8 bits
1
D19 0 1
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Application Information
Figure 5 - QR221BPF Application Example, 915.0 MHz
The MICRF221 receiver can be fully tested by using one of the many evaluation boards designed at Micrel for this device. As an entry level, the QR221BPF (Figure 5) offers a good start for most applications. It has a connector for a whip antenna (ANT1), a bandpass filter front end (L1 & C8) as a pre-selector filter, and a matching network (C3 & L2). It also includes the minimum components required to make the device work, which are: a crystal, CAGC, and CTH capacitors. An RF connector (J2) can be used instead of the whip antenna when tests require an RF signal generator. Figure 5 shows the entire schematic for 915.0MHz. Other frequencies can be used. The values needed for the various components are listed in the tables below. 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/(2xPIx(SQRT L1xC8))
Table 2 shows the most used frequency values.
Freq (MHz) 868.35 915.0 916.5 C8 (pF) 2.7 2.7 2.7 L1(nH) 12 11 11
Table 2. Band-Pass-Filter Front-End Values
There is no need for the band-pass filter front end in applications where it is proven that the outside band noise does not cause a problem. The MICRF221 receiver incorporates image reject mixers that improve the selectivity and rejection of outside band noise significantly.
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Matching Calculations Capacitor C3 and inductor L2 form the L-shaped 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 calculates the values using the equations below, and another by using a Smith chart. The Smith chart is made easier by using software that plots the values of the components C3 and L2, such as WinSmith by Noble Publishing. To calculate matching values, you need to know the input impedance of the device. Table 3 shows the input impedance of the MICRF221 receiver and suggested matching values for the most used frequencies. These suggested values may be different if your layout is different from the layout for the QR221BPF evaluation board.
Freq (MHz) 868.35 915.0 916.5 C3 (pF) 1.2 1.2 1.2 L2(nH) 9.5, Coilcraft 8.7, Coilcraft 8.7, Coilcraft Z device () 9.4-j71.8 9.0-j67.4 8.5-j68.0 Figure 6. Device's Input Impedance, Z = 9.0 - j67.4
Table 3. Matching Values for the Most Used Frequencies
For the frequency of 915.0MHz, the input impedance is Z = 9.0-j67.4. The matching components are calculated by: Equivalent parallel = B = 1/Z = 1.95 + j14.6 msiemens Rp = 1 / Re (B); Xp = 1 / Im (B) Rp = 513; Xp = 68.5 Q = SQRT (Rp/50 + 1) Q = 3.35 Xm = Rp / Q Xm = 153.1 Resonance Method For L-shape Matching Network: Lc = Xp / (2xPixf); Lp = Xm / (2xPixf) L2 = (LcxLp) / (Lc + Lp); C3 = 1 / (2xPixfxXm) L2 = 8.2nH C3 = 1.14pF Doing the same calculation, example with the Smith Chart, it would appear as follows: First, plot the input impedance of the device (Z = 9.0 - j67.4) @ 915.0MHz.(Figure 6).
Because stray parasitic elements can be caused by both the printed circuit board as well as the components themselves, the values plotted are slightly different from the calculated ones. Therefore, one plots the shunt inductor (8.7nH, from Coilcraft) and the series capacitor (1.2pF) for the desired input impedance (Figure 7). One can then see the matching leading to the center of the Smith Chart or close to 50.
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RF Ocsillator Calculation Crystal Y1 is the reference clock for all the device's internal circuits. Internally, the device has a Pierce Oscillator configuration, requiring the external capacitors, C9 and C10, to adjust the crystal center frequency. The exact values for these capacitors depend on the printed circuit board's stray capacitance. For example, with a top ground plane or longer traces, the value of these capacitors will be less than 10pF since there will be more stray capacitance. If a different layout from the one presented here is used, the capacitor values are optimized by getting the best sensitivity of the device. Crystal characteristics of 10pF load capacitance, 30ppm, ESR < 200, -40C to +105C temperature range are desired. Table 4 shows the crystal frequencies and two of Micrel's approved crystal manufactures (www.hib.com.br or www.abracon.com). Crystal frequency is calculated using: REFOSC = RF Carrier/(64+(1.1/12)) The local oscillator is a low side injection type, so for the 915.0MHz carrier, the local oscillator is calculated by: 64 x REFOSC = RF Local OSC 64 x 14.27643MHz = 913.69MHz That is, its frequency is below the RF carrier frequency and the image frequency is below the LO frequency. See Figure 8. The product of the incoming RF signal and local oscillator signal will yield the IF frequency, which is demodulated by the detector circuits.
Figure 7. Plotting the Shunt Inductor and Series Capacitor
Figure 8. Low Side Injection Local Oscillator
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REFOSC (MHz) 13.54856 14.27643 14.29983
Carrier (MHz) 868.35 915.0 916.5
HIB Part Number SA-13.548560-F-10-H-30-30-X SA-14.276430-F-10-H-30-30-X SA-14.299830-F-10-H-30-30-X
Abracon Part Number ABLS-13.54860MHz-10-J4Y ABLS-14.276430MHz-10-J4Y ABLS-14.299830MHz-10-J4Y
Table 4. Crystal Frequency and Vendors Part Number
Demodulation Bandwidth Calculation JP1 and JP2 are used to select the bandwidth for the demodulator. To set the bandwidth correctly, it is necessary to know the shortest pulse width of the encoded data sent in the transmitter. As shown in the example of the data profile in the Figure 9 below, PW2 is shorter than PW1, so PW2 should be used for the demodulator bandwidth calculation which is found by calculating 0.65/shortest pulse width. After this value is found, the setting should be done according to Table 5. 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, the bandwidth required would be 32.5kHz (0.65 / 20sec), which exceeds the maximum bandwidth of the demodulator circuit. If you try to exceed the maximum bandwidth, the pulse will appear stretched or wider.
SEL0 JP1, D3 Short Open Short Open SEL1 JP2, D4 Short Short Open Demod. BW (hertz) 1712 3425 6850 Shortest Pulse (sec) 380 190 95 Maximum baud rate for 50% Duty Cycle (hertz) 1316 2632 5264
data packets and if the data pattern has or does not have a preamble. See Figure 9 for an example of a data profile.
PREAMBLE HEADER 1 2 3 4 5 6 7 8 9 10 t1 t2 PW2 = NARROWEST PULSE WIDTH t1 & t2 = DATA PERIOD PW1 PW2
Figure 9. Example of a Data Profile
For best results C4 and C6 should be optimized for the data pattern used. As the baud rate increases, the capacitor values decrease. Table 6 shows suggested values for Manchester Encoded data at a 50% duty cycle.
SEL0 JP1 Short Open Short Open SEL1 JP2 Short Short Open Open Demod. BW (hertz) 1712 3425 6850 13700 CTH CAGC
100nF 47nF 22nF 10nF
4.7F 2.2F 1F 0.47F
Table 6. Suggested C6 (CTH) and C4 (CAGC) Values
Open 13700 47 10528 Table 5. JP1 and JP2 setting, 915 MHz
This device is capable of higher baud rates when the serial bit D16 is programmed high. More detail is provided on the following pages. CTH and CAGC Selection Capacitors C6 (CTH) and C4 (CAGC) provide time base reference for the data pattern received. These capacitors are selected according to the data profile, pulse duty cycle, dead time between two received October 2008
JP4 (pins 5 and 6) is a jumper used to configure the digital squelch function. When pin 6 (SQ) is held high jumpered-to-VDD), there is no squelch applied to the digital circuits and pin 10 (DO, data out) has a hash signal. When pin 6 (SQ) is low, the DO pin activity is considerably reduced. It will have more or less activity than is shown in Figure 11 depending upon the outside band noise. The penalty for using squelch is a delay in getting a good signal at the DO pin, that is, it takes longer for the data to show. The delay is dependent upon many factors such as RF signal intensity, data profile, data rate, CTH and CAGC capacitor values and outside band noise. See Figures 10 and Figure 11.
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MICRF221 external control of the AGC voltage may vary from lot-to-lot and may not work the same for several devices. 5V Operation 5-volt operation can be obtained by replacing R5, R6, and R7 (0 resistors) to R5 = 150, R6 = R7 = 33 k. The 5-volt source must be regulated and guaranteed never to exceed 5V. DO is equal to VDD levels. Four other pins are worthy of comment. They are the DO, RSSI, SHDN, and SCLK pins. DO Pin The DO pin has a driving capability of 0.4mA. This is good enough for most of the logic families ICs on the market today. It also works as an input when programming the device for the serial register control RSSI Pin The RSSI pin provides a transfer function of RF signal intensity versus voltage. It is useful to 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. SCLK Pin Serial interface input clock is a CMOS Schmitt input. A 25k pull-down is present when device is in shutdown mode. See "Programming the Device" section for timing diagram and functional operation SHDN (Shut Down) Pin The shut down pin (SHDN) can be used to save energy. If its level is close to VDD (SHDN = 1), the device will not be in operation. Its DC current consumption is less than 1A (R3 must be removed). This input pin is designed with a weak pull-up. The pull-up current is decreased once the input has switched above the threshold level, that is, the device is shut down and progressively decreases to levels below 1A. When shut down pin is toggling from high to low (getting out of shut down mode), there is some time required for the device to come to steady-state mode and some time needed for data to appear at the DO pin. The actual time required is dependent upon several factors, such as temperature, the crystal used and if the there is an external oscillator coupled through C2 with faster startup time. Normally (assuming the suggested crystal vendors are used), the preamble data will appear at the DO pin at approximately 1msec time, and 2msec over the temperature range of the device. 16
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Figure 10. Data Out Pin with No Squelch (SQ = 1)
Figure 11. Data Out Pin with Squelch (SQ = 0)
Other components used include: C5 is a decoupling capacitor for the Vdd line. R4 should be referenced to ground when a microcontroller connection is not made and kept low by the microcontroller when not programming the device. R3 is the reference 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. R1 and R2 form a voltage divider for the AGC pin. One can purposely decrease the device sensitivity by forcing a voltage to this AGC pin. Special care is needed when doing this operation, as an October 2008
Micrel Inc.
T6 SCLK T7 BIT TIME 0 BIT TIME 1 BIT TIME 2
MICRF221
T1
T2 T3
T4
T5
T8
T9
"19" DO AS OUTPUT DO INPUT BITS: D19
"0" D18
"0" D17
"1"
Figure 12. Serial Interface Start Sequence
When using an external oscillator or reference oscillator signal, the maximum level should not exceed 1.5VPP. See Figure 13. Channel 4 is the transmitted data, which is synchronized with the shutdown shown in the oscilloscope (channel 2). Data out is shown on channel 1 and, as seen below, the preamble data starts to appear just over 1msec after the shutdown pin cycle low to high. Also note that when squelch is used time for data to appear is increased.
device through the DO pin toggling from low to data * * High Demodulator faster baud rates Bandwidth, for
Parallel input pins SEL0, SEL1, and SQ can be programmed using the serial interface
Figure 13. Time-to-Preamble Data after Shut Down Cycle, Room Temperature
Programming the Device Several additional functions are available by the serial interface. They are: * * * Desense, sensitivity to reduce the device
Slice Level, to further optimize data profile demodulation Autopoll Mode, to wake an external
Programming the device is accomplished by the use of pins DO and SCLK. Normally, pin 10 (DO) is outputting data and needs to switch to an input pin made by the start sequence, as shown at Figure 13. A high at the SCLK pin tri-states the DO pin, enabling the external drive into the DO pin with an initial low level. The start sequence is completed by taking SCLK low, then high while DO is low, followed by taking DO high, then low while SCLK is high. The serial interface is initialized and ready to receive the programming data. Bits are serially programmed starting with the most significant bit (MSB = D19) if all bits are being programmed until the least significant bit (LSB =D0) For instance, if only the desense bits D0, D1, and D2 are being programmed, then these are the only bits that need to be programmed with the start sequence D2, D1, D0, plus the stop sequence. Or, if only the squelch bit D17 is needed, then the sequence must be from start sequence, D17 through D0 plus the stop sequence, making sure the other bits (besides D17) are programmed as needed. It is recommended that all parallel input pins (SEL0, SEL1, and SQ) be kept high when using the serial interface. After the programming bits are finished, a stop sequence (as shown in Figure 14) is required to end the mode and make the DO pin as an output again. To do so, the SCLK pin is kept high while the DO pin changes from low to high, then low again, followed by the SCLK pin made low. Timing of the programming bits are not critical, but should be kept as shown below: 17
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Micrel Inc. T1 < 0.1 us, Time from SCLK to convert DO to input pin T6 > 0.1 us, SCLK high time T7 > 0.1 us, SCLK low time T2, T3, T4, T5, T8, T9, T10 > 0.1 us
BIT TIME 18 BIT TIME 19 SCLK
MICRF221 Only bits 19 and 18 High, Figure 17.
T10 "1" D1 "0" DO "1" DO DO PIN AS OUTPUT
Figure 14. Serial Interface Stop Sequence
Serial Interface Examples All bits (D19 through D0) low (channel 1 is the DO pin, and Channel 2 is the SCLK pin), see Figure 15.
Figure 17 D19 = D18 = 1.
Figure 15. All bits 0s.
All bits (D19 through D0) High, Figure 16.
Autopoll example, Figure 18. D0 = D1 = D2 = 0, no desense D3 = D4 = 0, demodulator bandwidth = 1712 hertz, 1 kHz baud rate, pulse = 500 usec, required demodulator bandwidth is 0.65/500usec = 1300 hertz D5 = D6 = 1, Slice level = 50% D7 = 0, D8 = 1, bit check = 4 bits. This is the time the device is ON checking for four consecutive valid windows. D9 = D10 = 1, D11 = 0, data rate is 1 kHz, (500 usec pulses), window set to 433 usec (< 500 usec) D12 = D13 = 0, D14 = 1, sleep timer set to 160 msec, that is, 4 bit is ON and 160 msec is OFF. D15 = 1, device is placed in autopoll D16 = 0, normal demodulator bandwidth D17 = 0, squelch is OFF D18 = 1, watchdog timer is OFF D19 = 0, no RSSI offset From MSB to LSB, see Table 7:
D19 D18 D17 D16 D15 D14 D13 D12
0 D11 0 D4 0
Figure 16 All bits 1s.
1 D10 1 D3 0
0 D9 1 D2 0
0 D8 1 D1 0
1 D7 0 D0 0
1 D6 1
0 D5 1
0
Table 7. Autopoll example bit sequence
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Figure 18. Autopoll example
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MICRF221
PCB LAYOUT RECOMMENDATIONS
PCB Considerations and Layout Figures 19 to 22 below, show some of the printed circuit layers for the QR221BPF board, refer to Figure 5. Use the Gerber files provided (downloadable from the Micrel Website at: www.micrel.com ), which have the remaining layers needed to fabricate this board. When copying or making one's own boards, make traces as short as possible. Long traces alter the matching network and the values suggested are no longer 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 = one or more VIAs. The ground plane must be solid and, if possible, without interruptions. Avoid a ground plane on the top layer next to the matching element, as it will normally add additional stray capacitance, which changes the matching. Do not use phenolic material; use only FR4 or better materials, since phenolic material is conductive above 200MHz. The RF path should be as straight as possible, avoiding loops and unnecessary turns. Separate the ground and VDD lines from other circuits (microcontroller, etc). Known sources of noise should be positioned as far as possible from the RF circuits. Avoid thick traces. The higher the frequency, the thinner the trace should be to minimize losses in the RF path.
Figure 19. QR221BPF Top Layer
Figure 20. QR221BPF Bottom Layer, Mirror Image
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Figure 21. QR221BPF Top Silkscreen Layer
Figure 22. QR221BPF Bottom Silkscreen Layer, Mirror Image
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Figure 23. QR221BPF Dimensions (inches)
QR221BPF Bill of Materials, 915.0 MHz
Item ANT1 C3 C4 C6,C5 C8 C9,C10 C2 JP1,JP2 JP3,JP4 J1 J2 L1 L2 R1,R2 R3,R4 R5,R6, R7 Y1 U1 HC49 MICRF221AYQS www.hib.com.br www.abracon.com Micrel Semiconductor 14.27643MHz Crystal, 10pF load,, 30ppm, -40 to +105 operating temperature QSOP16 1 1 Vishay Vishay 0603CS-11NXGB 0603CS8N7XJB Coilcraft Coilcraft GRM39COG2R7C50 GRM39COG100D50 GRM39X7R102K50 GRM39COG1R2C50 MuRata Murata / Vishay Murata / Vishay MuRata MuRata MuRata Vishay Part Number Manufacturer Description 50- Ant78.7mm (3.1 inches) 20 AWG, rigid wire 1.2pF , 0402/0603 4.7F, 0603/0805 0.1F, 0402/0603 2.7pF, 0402/0603 10pF, 0402/0603 (np)1nF, 0402/0603, not placed short, 0402/0603, 0 resistor open, 0402/0603, not placed CON7 (np)SMA, not placed 11nH 2%, 0402/0603 8.7nH 5%, 0402/0603 (np) 0402/0603, not placed 100k , 0402/0603 0 , 0402/0603 Qty. 1 1 1 2 1 2 1 2 2 1 1 1 1 2 2 3
Table 8. QR221BPF Bill of Materials, 915.0 MHz
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QR221BPF Bill of Materials, 916.5 MHz
Item ANT1 C3 C4 C6,C5 C8 C9,C10 C2 JP1,JP2 JP3,JP4 J1 J2 L1 L2 R1,R2 R3,R4 R5,R6, R7 Y1 U1 HC49 MICRF221AYQS www.hib.com.br www.abracon.com Micrel Semiconductor 14.29983MHz Crystal, 10pF load,, 30ppm, -40 to +105 operating temperature QSOP16 1 1 Vishay Vishay 0603CS-11NXGB 0603CS8N7XJB Coilcraft Coilcraft GRM39COG2R7C50 GRM39COG100D50 GRM39X7R102K50 GRM39COG1R2C50 MuRata Murata / Vishay Murata / Vishay MuRata MuRata MuRata Vishay Part Number Manufacturer Description 50- Ant78.7mm (3.1 inches) 20 AWG, rigid wire 1.2pF , 0402/0603 4.7F, 0603/0805 0.1F, 0402/0603 2.7pF, 0402/0603 10pF, 0402/0603 (np)1nF, 0402/0603, not placed short, 0402/0603, 0 resistor open, 0402/0603, not placed CON7 (np)SMA, not placed 11nH 2%, 0402/0603 8.7nH 5%, 0402/0603 (np) 0402/0603, not placed 100k , 0402/0603 0 , 0402/0603 Qty. 1 1 1 2 1 2 1 2 2 1 1 1 1 2 2 3
Table 9. QR221BPF Bill of Materials, 916.5 MHz
QR221BPF Bill of Materials, 868.35 MHz
Item ANT1 C3 C4 C6,C5 C8 C9,C10 C2 JP1,JP2 JP3,JP4 J1 J2 L1 L2 R1,R2 0603CS-12NXGB 0603CS9N5XJB Coilcraft Coilcraft GRM39COG2R7C50 GRM39COG100D50 GRM39X7R102K50 GRM39COG1R2C50 MuRata Murata / Vishay Murata / Vishay MuRata MuRata MuRata Vishay Part Number Manufacturer Description 50- Ant83.8mm (3.3 inches) 20 AWG, rigid wire 1.2pF , 0402/0603 4.7F, 0603/0805 0.1F, 0402/0603 2.7pF, 0402/0603 10pF, 0402/0603 (np)1nF, 0402/0603, not placed short, 0402/0603, 0 resistor open, 0402/0603, not placed CON7 (np)SMA, not placed 12nH 2%, 0402/0603 9.5nH 5%, 0402/0603 (np) 0402/0603, not placed Qty. 1 1 1 2 1 2 1 2 2 1 1 1 1 2
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Item R3,R4 R5,R6,R7 Y1 U1 HC49 MICRF221AYQS Part Number Manufacturer Vishay Vishay www.hib.com.br www.abracon.com Micrel Semiconductor Description 100k , 0402/0603 0 , 0402/0603 13.54856MHz Crystal, 10pF load,, 30ppm, -40 to +105 operating temperature QSOP16
MICRF221
Qty. 2 3 1 1
Table 8. QR221BPF Bill of Materials, 868.35 MHz
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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 a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2008 Micrel, Incorporated.
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