MICRF218_11 [MICREL]
3.3V, 315/433MHz Wide-IF Bandwidth ASK Receiver; 3.3V ， 315 / 433MHz的宽IF带宽ASK接收器
| 型号： | MICRF218_11 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | 3.3V, 315/433MHz Wide-IF Bandwidth ASK Receiver |
| 文件： | 总23页 (文件大小：823K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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, medium-
grade (~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.
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
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.
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
U1 MICRF218AYQS
1
2
3
4
5
6
7
8
16
RO1
RO2
NC
C2
15
14
13
12
11
10
9
GNDRF
ANT
1.5pF 50V
RSSI
CAGC
CTH
SEL1
DO
RSSI
GNDRF
VDD
+3V
L1
39nH
C1
6.8pF
L2
68nH
IF_BW
SEL0
C4
0.1µF
16V
C5
4.7µF
6.3V
DO
C3
0.1µF 16V
SHDN
GND
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
M9999-111111
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November 2011
Micrel
MICRF218
315MHz/315.802, 900Hz Baud Rate Example
Pin Configuration
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
RO1
GNDRF
ANT
RO2
NC
RSSI
CAGC
CTH
SEL1
DO
GNDRF
Vdd
IF_BW
SEL0
SHDN
GND
MICRF218AYQS
Pin Description
16-Pin
QSOP
Pin
Name
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.
1
2
3
RO1
GNDRF
ANT
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.
4
5
GNDRF
VDD
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.
6
IF_BW
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)
7
SEL0
8
9
SHDN
GND
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.
16-Pin
QSOP
Pin
Name
Pin Function
10
DO
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)
11
SEL1
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.
12
CTH
13
14
15
16
CAGC
RSSI
NC
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.
RO2
2
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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
20:1 Duty Cycle, fRX = 315 MHz
0.2
5.5
mA
mA
MICRF218 Operating
Supply Current
IDD
Continuous Operation, fRX = 433.92 MHz
20:1 Duty Cycle, fRX = 433.92 MHz
0.3
1
mA
µA
Ishut
Shut down Current
RF/IF Section
Image Rejection
20
dB
1st IF Center
Frequency
fRX = 315 MHz, Narrow IF
0.98
MHz
f
RX = 433.92 MHz, Narrow IF
fRX = 315 MHz, Wide IF
RX = 433.92 MHz, Wide IF
fRX = 315 MHz, Narrow IF (50 ohms)
RX = 433.92 MHz, Narrow IF (50 ohms)
1.4
1.8
MHz
MHz
MHz
dBm
dBm
dBm
dBm
1st IF Center
Frequency
f
2.4
-108
-108
-106
-106
Receiver Sensitivity @
1kbps
f
fRX = 315 MHz, Wide IF (50 ohms)
fRX = 433.92 MHz, Wide IF (50 ohms)
Receiver Sensitivity @
1kbps
fRX = 315 MHz, Narrow IF
fRX = 433.92 MHz, Narrow IF
fRX = 315 MHz, Wide IF
400
550
1000
1500
kHz
kHz
kHz
kHz
IF Bandwidth
fRX = 433.92 MHz, Wide IF
fRX = 315 MHz
16-j211
Ω
Ω
Antenna Input
Impedance
fRX = 433.92 MHz
9.54-j152
Receive Modulation
Duty Cycle
Note 6
20
80
%
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MICRF218
Symbol Parameter
Condition
ATTACK / tDECAY
Min
Typ
Max
Units
AGC Attack / Decay
Ratio
t
0.1
TA = 25ºC
± 2
nA
nA
AGC pin leakage
current
TA = +85ºC
± 800
RFIN @ -50dBm
RFIN @ -110dBm
1.13
1.70
V
V
AGC Dynamic Range
@ fRX = 433.92MHz
Reference Oscillator
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
9.8131
9.78823
13.5178
MHz
MHz
MHz
MHz
Frequency
13.48352
300
Input Impedance
Input Range
kΩ
Vp-p
µA
0.2
1.5
Source Current
V(REFOSC) = 0V
3.5
Demodulator
CTH Source
Impedance
fREFOSC = 9.8131MHz, 315MHz, Note 8
165
kΩ
TA = 25ºC
TA = +85ºC
SEL0=0, SEL1=0
SEL0=0, SEL1=1
SEL0=1, SEL1=0
SEL0=1, SEL1=1
± 2
CTH Leakage Current
nA
± 800
1180
2360
4720
9420
Hz
Hz
Hz
Hz
Demodulator Filter
Bandwidth @ 315
MHz
CTH Source
Impedance
fREFOSC = MHz, 433.92MHz, note 8
120
kΩ
TA = 25ºC
TA = +85ºC
SEL0=0, SEL1=0
SEL0=0, SEL1=1
SEL0=1, SEL1=0
SEL0=1, SEL1=1
± 2
± 800
1625
3250
6500
13000
CTH Leakage Current
nA
Hz
Hz
Hz
Hz
Demodulator Filter
Bandwidth @ 433.92
MHz
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MICRF218
Symbol Parameter
Digital / Control Functions
Input High Voltage
Condition
Min
Typ
Max
Units
0.8VDD
Pins DO (As input), SHDN
Pins DO (As input), SHDN
V
V
0.2VDD
Input Low Voltage
Source @ 0.8 Vdd
Sink @ 0.2 Vdd
260
600
DO pin output current
µA
Output rise and fall
times
CI = 15 pF, pin DO, 10-90%
-90 dBm to -40 dBm
2
µsec
RSSI
RSSI DC Output
Voltage Range
0.22
to 2
V
mV/
dBm
RSSI response slope
35
RSSI Output Current
±1.5
200
mA
RSSI Output
Impedance
Ω
50% data duty cycle, input power to
Antenna = -20 dBm
RSSI Response Time
0.3
Sec
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 )
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MICRF218
Typical Characteristics
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MICRF218
7
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MICRF218
LO Leakage in RF Port
Re-radiation from MICRF218 Antenna Port
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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.
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.
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.
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.
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 pre-
selector band pass 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
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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.
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.
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:
The crystal frequency for Wide Bandwidth IF
operation is given by:
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.
OperatingFreq
REFOSC
MHz
(1)
2.178
12
(32
)
The crystal frequency for Narrow Bandwidth IF
operation is given by:
OperatingFreq
REFOSC
MHz
(2)
Scenario 2:
1.198
12
(32
)
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.
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:
IF_Parameter IF_Parameter @ 433.92 MHz
(3)
Operating Freq (MHz)
433.92(MHz)
*
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
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MICRF218
J4
J1
IF BANDWIDTH
CONTROL
1
2
1
2
EXTERNAL REFERENCE
OSCILLATOR INPUT
REFOSC
CON2
C1
NP
VDD = WIDE BANDWIDTH
0V = NARROW BANDWIDTH
+3V
Y1
Y2
JPR1
0 OHMS
JPR2
NP
9.8131MHz
12.1287MHz
U1 MICRF218AYQS
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
RO1
RO2
NC
J2
RF IN
L4
100nH
C2
2.2pF
L3
100nH
R1
NP
GNDRF
ANT
RSSI
CAGC
CTH
SEL1
DO
TSDF1220W
Q1
TSDF1220W
Q2
GNDRF
VDD
+3V
R2
NP
C3
33pF
L2
3.9nH
IF_BW
SEL0
SHDN
C5
100nF
C4
0.047µF
C5
4.7µF
R7
100k
GND
R11
100k
R3
NP
R5
100K
Notes:
1. 0V = Common
C7
NP
R4
0 OHMS
2. VDD Input = 3.0 to 3.3V
3. Ref-Osc Control:
R6
10k
+3V
0V = 315 MHz Operation,
VDD = 390.1 MHz Operation
R8
10k
R9
10k
L3
ZCB-0603
J3
3.0 to 3.3V
3.0 to 3.3V
COM
1
2
3
4
5
6
7
R10
100k
+3V
SHDN
DO
REF-OSC CNTR
COM
DATA OUT
NP= Not Placed
Figure 4. Dual Frequency QR218BP_SWREF, 315 MHz and 390 MHz
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MICRF218
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.
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
Bandwidth will scale directly with operating frequency
(equation 3). Higher operating frequency will have the
wider IF bandwidth.
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.
Given one operating frequency, the other frequency
can be determined.:
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.
(384 1.198)
(384 - 2.178)
(4)
Freq2 Narrow Bandwidth Freq1Wide Bandwidth
*
AGC Comparator
(384 2.178)
(384 -1.198)
(5)
Freq2 Wide Bandwidth Freq1Narrow Bandwidth
*
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
Reference Control
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:
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
(Operating Freq)
(6)
BW Operating Freq BW @433.92MHz *
433.92
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)
1625Hz
0
1
0
1
0
0
1
1
3250Hz
6500Hz
13000Hz
- default
Table 1. Demodulation BW Selection
Figure 6. Reference Oscillator Circuit
The reference oscillator in the MICRF218 (Figure 6)
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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.
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.
See equation (1) and (2) to calculate reference
oscillator crystal frequency for either narrow or wide
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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.
Products application note.
Freq (MHz)
315.0
C9 (pF)
L3(nH)
1.2
1.2
1.2
1.5
75
43
36
30
390.0
418.0
433.92
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).
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.
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:
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
1
f
(2 * L1* C8)
14
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MICRF218
Table 3 shows the most used frequency values.
Q = SQRT (Rp/50 + 1)
Q = 7.06
Freq (MHz)
315.0
C8 (pF)
6.8
L1(nH)
39
Xm = Rp / Q
Xm = 345.8Ω
390.0
6.8
24
Resonance Method For L-shape Matching Network:
418.0
6.0
24
Lc = Xp / (2×Pi×f);
L2 = (Lc×Lp) / (Lc + Lp);
L2 = 38.9nH
Lp = Xm / (2×Pi×f)
433.92
5.6
24
C3 = 1 / (2×Pi×f×Xm)
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.
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).
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)
315.0
C3 (pF)
1.5
L2(nH)
68
Z device (Ω)
16.3 -j210.8
8.26 – j163.9
11.1 – j161.9
9.54 – j152.3
390.0
1.2
47
418.0
1.2
43
433.92
1.1
39
Figure 8. Device’s Input Impedance, Z = 9.54-j152Ω
Table 4. Matching values for the most used frequencies
For the frequency of 433.92MHz, the input impedance
is Z = 9.54 – j152.3Ω. The matching components are
calculated by:
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.
Equivalent parallel = B = 1/Z = 0.410 + j6.54
msiemens
Rp = 1 / Re (B);
Xp = 1 / Im (B)
Rp = 2.44kΩ;
Xp = 345.8Ω
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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)
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
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
390.0
418.0
433.92
315
390.0
418.0
433.92
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.
Maximum
baud rate for
50% Duty
Demod.
BW
(hertz)
Shortest
Pulse
(µsec)
SEL0
JP1
SEL1
JP2
Cycle (hertz)
Short
Open
Short
Open
Short
Short
Open
Open
1625
3250
6500
13000
400
200
100
50
1250
2500
5000
10000
Table 6. JP1 and JP2 setting, 433.92 MHz
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.
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.
Maximum
baud rate for
50% Duty
Demod.
Shortest
Pulse
(µsec)
SEL0
JP1
SEL1
JP2
BW
(hertz)
Cycle (hertz)
Image
Desired
Signal
Short
Open
Short
Open
Short
Short
Open
Open
1565
3130
6261
12523
416
208
104
52
1204
2408
4816
9633
Frequency
Table 7. JP1 and JP2 setting, 418.0 MHz
-fLO
f (MHz)
Maximum
baud rate for
50% Duty
Figure 10. Low Side Injection Local Oscillator
Narrow and Wide Band Crystal Part Numbers,
Demod.
Shortest
Pulse
(µsec)
SEL0
JP1
SEL1
JP2
BW
(hertz)
WB = IF Wide Band, NB = IF Narrow Band
Cycle (Hertz)
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.
Short
Open
Short
Open
Short
Short
Open
Open
1460
2921
5842
11684
445
223
111
56
1123
2246
4493
8987
Table 8. JP1 and JP2 setting, 390.0 MHz
Maximum
baud rate for
50% Duty
Demod.
Shortest
Pulse
(µsec)
SEL0
JP1
SEL1
JP2
BW
(hertz)
Cycle (Hertz)
Short
Open
Short
Open
Short
Short
Open
Open
1180
2360
4720
9400
551
275
138
69
908
1815
3631
7230
Table 9. JP1 and JP2 setting, 315.0 MHz.
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MICRF218
Selection of CTH and CAGC Capacitors
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.
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
10
1
2
3
4
5
6
7
8
9
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.
Demod.
BW
(hertz)
Cth
Cagc
SEL0
JP1
SEL1
JP2
(C6)
(Cagc)
Short
Open
Short
Open
Short
Short
Open
Open
1625
3250
6500
13000
100nF
47nF
22nF
10nF
4.7µF
2.2µF
1µF
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
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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
Part Number
Manufacturer
Description
Helical PCB Antenna Pattern
Qty.
1
0
1
1
(np)50-ohm Ant 168mm 20 AWG, rigid wire
1.5pF , 0402/0603
MuRata
Murata / Vishay
Murata/Vishay
Murata / Vishay
Murata
C4
4.7µF, 0805
C3
1.1pF, 0402/0603
C6,C5
C8
0.1µF, 0402/0603
2
1
5.6pF, 0402/0603
JP1,JP
2, JP3
Vishay
short, 0402, 0Ω resistor
2
JP4
J2
(np) not placed
(np) not placed
CON6
0
0
1
J3
Coilcraft / Murata /
ACT1
L1
L2
L3
24nH 5%, 0402/0603
39nH 5%, 0402/0603
30nH 2%, 0402/0603
(np) 0402, not placed
1
1
1
0
Coilcraft / Murata /
ACT1
Coilcraft / Murata /
ACT1
R1,R2,
R4
R3
Y1
Vishay
100kΩ , 0402
1
0
1
1
HCM49
HC49/US
www.hib.com.br
www.hib.com.br
Micrel Semiconductor
(np)13.51783MHz Crystal
13.51783MHz Crystal
QSOP16
Y1A
U1
MICRF218AYQS
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.
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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.
© 2007 Micrel, Incorporated.
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MICRF218
Revision History
Date
Edits by:
Revision Number
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