Datasheet MICRF218 Datasheet (Micrel)

General Description

MICRF218

3.3V, QwikRadio® 300 MHz to 450 MHz Receiver

Features

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 rej ection functions are built-in. D ual IF
bandwidths enable the MICRF218 to capture signals
from either high performance or low cost transmitters.
In addition, all post-det ec tio n data filtering is provi ded o n
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 k Hz. The user only needs to
program the device with a set of easily determined
values, based upon d ata rate, code modulation form at,
and desired duty-c ycle operation . The MICRF 218 h as 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 ac commodate two ref erence crystals
with the use of an external switch. Once the system
detects a strong jamm ing signal on one frequency, the
MICRF218 can switch to another frequency via a
switching crystal. This is the ideal receiver for “Jam
Avoidance”.

• 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 m ode)

• Analog RSSI Output

• No IF filter required

• Excellent selectivity and noise rejection

• Low external part count

Ordering Information

Part Number Temperature Range Package

MICRF218AYQS –40° to +85°C 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 [phone] • fax + 1 [phone] • http://www.micrel.com

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Application Example

ANT
PCB Pattern

L1
39nH

Pin Configuration

Pin Description

C2

1.5pF 50V

C1

6.8pF

L2
68nH

IF_BWCONTROL

315MHz/315.802, 900Hz Baud Rate Example

1

RO1

2

GNDRF

3

ANT

4

GNDRF

5

+3V

C3

0.1µF 16V

1

RO1

GNDRF

GNDRF

2
3

ANT

4
5

Vdd

6

IF_BW

7

SEL0

8 9

SHDN GND

VDD

6

IF_BW

7

SEL0

89

SHDN GND

MICRF218AYQS

Y1

9.8131MHz

U1 MICRF218AYQS

RO2

NC

RSSI

CAGC

CTH

SEL1

DO

16

RO2

15

NC

14

RSSI

13

CAGC

12

CTH

11

SEL1

10

DO

16
15
14
13
12
11
10

DO

RSSI

C4

0.1µF
16V

C5

4.7µF

6.3V

16-Pin
QSOP

1 RO1

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.

2 GNDRF Negative supply connection associated with ANT RF input.
3 ANT

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 GNDRF Negative supply connection associated with ANT RF input.
5 VDD Positive supply connection for all chip functi on s.

6 IF_BW

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
7 SEL0

demodulator low pass filter bandwidth. (See filter table for SEL0 and SEL1 in application

subsection)
8 SHDN Shutdown logic control input. Active internal pull-up and must be pulled low for Normal Operation.
9 GND Negative supply connection for all chip functions except RF input.

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16-Pin
QSOP

10 DO Demodulated data output.

11 SEL1

12 CTH

13 CAGC AGC filter capacitor. A capacitor, normally greater than 0.47uF, is connected from this pin to GND
14 RSSI
15 NC Not Connected
16 RO2

Pin

Name

Pin Function

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.

Received signal strength indication output. Output is from a buffer with 200 ohms typical output

impedance.

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.

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Absolute Maximum Ratings

Supply Voltage (VDD) ................................................+5V

Input Voltage.............................................................+5V

Junction Temperature..........................................+150°C

Lead Temperature (soldering, 10sec.) ..................260°C

Storage Temperature (T

Maximum Receiver Input Power........................ +10dBm

ESD Rating(3) ..........................................................3KV

) ....................-65ºC to +150°C

S

(1)

Operating Ratings

Supply voltage (VDD) ............................+3.0V to +3.6V

Ambient Temperature (T
Input Voltage (V

Maximum Input RF Power ..............................–20dBm

Operating Frequency ..........................300 to 450 MHz

).......................................3.6V (Max)

IN

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 mA

IDD

Ishut Shut down Current

MICRF218 Operating
Supply Current

Continuous Operation, fRX = 433.92 MHz 5.5 mA
20:1 Duty Cycle, f

= 433.92 MHz 0.3 mA

RX

RF/IF Section

Image Rejection 20 dB

st

IF Center

1
Frequency

fRX = 315 MHz, Narrow IF 0.98 MHz
f

= 433.92 MHz, Narrow IF 1.4 MHz

RX

(2)

)..................–40°C to +85°C

A

1 µA

st

IF Center

1
Frequency

Receiver Sensitivity @
1kbps

Receiver Sensitivity @
1kbps

IF Bandwidth

Antenna Input
Impedance

Receive Modulation
Duty Cycle

fRX = 315 MHz, Wide IF 1.8 MHz
f

= 433.92 MHz, Wide IF 2.4 MHz

RX

fRX = 315 MHz, Narrow IF (50 ohms) -108 dBm
f

= 433.92 MHz, Narrow IF (50 ohms) -108 dBm

RX

fRX = 315 MHz, Wide IF (50 ohms) -106 dBm
f

= 433.92 MHz, Wide IF (50 ohms) -106 dBm

RX

fRX = 315 MHz, Narrow IF 400 kHz
fRX = 433.92 MHz, Narrow IF 550 kHz
fRX = 315 MHz, Wide IF 1000 kHz
f

= 433.92 MHz, Wide IF 1500 kHz

RX

fRX = 315 MHz 16-j211 Ω

= 433.92 MHz 9.54-j152 Ω

f

RX

Note 6 20 80 %

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Symbol Parameter Condition Min Typ Max Units

Reference Oscillator

Frequency

Input Impedance 300 kΩ
Input Range 0.2 1.5 Vp-p
Source Current V(REFOSC) = 0V 3.5 µA

Demodulator

CTH Leakage Current

CTH Leakage Current

AGC Attack / Decay
Ratio

AGC pin leakage
current

AGC Dynamic Range
@ fRX = 433.92MHz

CTH Source
Impedance

Demodulator Filter
Bandwidth @ 315
MHz

CTH Source
Impedance

Demodulator Filter
Bandwidth @ 433.92
MHz

t

ATTACK

/ t

0.1

DECAY

TA = 25ºC ± 2 nA

= +85ºC ± 800 nA

T

A

RFIN @ -50dBm 1.13 V
RFIN @ -110dBm 1.70 V

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

f

= 9.8131MHz, 315MHz, Note 8 165 kΩ

REFOSC

TA = 25ºC ± 2
TA = +85ºC ± 800

9.8131 MHz

9.78823 MHz

13.5178 MHz

13.48352 MHz

nA

SEL0=0, SEL1=0 1180 Hz
SEL0=0, SEL1=1 2360 Hz
SEL0=1, SEL1=0 4720 Hz
SEL0=1, SEL1=1 9420 Hz

f

= MHz, 433.92MHz, note 8 120 kΩ

REFOSC

TA = 25ºC ± 2
TA = +85ºC ± 800

nA

SEL0=0, SEL1=0 1625 Hz
SEL0=0, SEL1=1 3250 Hz
SEL0=1, SEL1=0 6500 Hz
SEL0=1, SEL1=1 13000 Hz

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Symbol Parameter Condition Min Typ Max Units
Digital / Control Functions

Input High Voltage Pins DO (As input), SHDN
Input Low Voltage Pins DO (As input), SHDN

Source @ 0.8 Vdd

DO pin output current

Output rise and fall
times

Sink @ 0.2 Vdd
CI = 15 pF, pin DO, 10-90% 2 µsec

0.8VDD

V

0.2VDD

260
600

V

µA

RSSI

RSSI DC Output
Voltage Range

RSSI response slope -90 dBm to -40 dBm 35

0.22
to 2

V

mV/

dBm

RSSI Output Current ±1.5 mA

/(T

ON

ON

RSSI Output
Impedance

200 Ω
50% data duty cycle, input power to

Antenna = -20 dBm

+ t

) = 50%; without preamble, duty cycle is TON/(T

OFF

REFOSC

REFOSC

TAB

MHz = ( f

TAB

MHz = ( F

= T

OFF

), compute new parameter value as the ratio:

REFOSC

), compute new parameter value as the ratio:

TAB

– TON.)

BURST

MHz /F

/ f

REFOSC

) × ( parameter at F

TAB

MHz ) × ( parameter at F

0.3 Sec

+ T

+ T

ON

OFF

. For any reference oscillator frequency other than one of the tabulated

T

MHz )

TAB

TAB

) = 50msec/(200msec) = 25%. TON is the (Average number of

QUIET

MHz )

RSSI Response Time

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 rat e). 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
T
1’s/burst) × bit time, and T

7. Parameter scales linearly with reference osci llator frequency f
frequencies (called F

Parameter at f

8. Parameter scales inversely with reference oscillator frequency fT. For any reference oscillator frequency other than one of the tabulated
frequencies (called F

Parameter at f

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Typical Characteristics

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LO Leakage in RF Port

Re-radiation from MICRF218 Antenna Port

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f

c

ANT

VDD

VSS

SEL0
SEL1

IF_ BW

SHDN

RF

Amp

f

SYNTHESIZER

Reference and Control

LO

Functional Description

UHF Downconverter

mixer

mixer

Wide / Narrow

RO1

Figure 1 Simplified Block Diagram

IF_BW

IMAGE
REJECT
FILTER

-f

CONTROL

REFERENCE

OSCILLATO R

Crystal

i

LOGIC

CAGC

AGC

IF

Amp

f

CONTROL

LOGIC

DO

RO2

Detector

Programmab l e

LowPassFilter

CONTROL

LOGIC

Slicing

Leve l

RSSI

OOK

Demodulator

SLICER

RSSI

DO

CTH

Receiver Operation

Figure 1 illustrates the basic structure of the
MICRF218. It is composed of three sub-bloc ks; Im age
Rejection UHF Down-converter with Switch-able Dual
IF Bandwidths, the O OK Dem odulator, and Reference
and Control Logics.

Outside the device, the MICRF218 req uires onl y three
components to operate: two capacitors (CTH, and
CAGC) and the ref erence frequenc y device, usua lly 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.

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LNA

The RF input signal is AC- coupled into th e gate circu it
of the grounded source LN A input stage. The LNA is
a Cascoded NMOS.

Mixers and Synthesizer

The LO ports of the Mixers are driven by quadrat ure
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 f requency at t wice the
IF frequency below the wanted signal. The local
oscillator is set to 32 times the crystal reference
frequency via a phase-loc ked 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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passes through a t hird order band pass filter. The IF
Band-Pass filters are fully integrated inside the
MICRF218. After filtering, four active gain controlled
amplifier stages en hance the IF signa l to proper level
for demodulation.

IF Bandwidth General Description

The MICRF218 has IF filt ers which m a y be conf igur ed
for operation in a narrow band or wide band mode
using the IF_BW pin. This pin must not be lef t f loa tin g ;
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 1500k Hz. W ith the us e of a 13. 5178MH z
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:

+

+

Freq Operating

2.178
12

Freq Operating

1.198
12

)

)

REFOSC

The crystal frequency for Narrow Bandwidth IF
operation is given by:

REFOSC

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:

=

(32

=

(32

=

⎛
⎜

*

⎜
⎝

(MHz) Freq Operating

)433.92(MHz

(1)

MHz

(2)

MHz

er IF_Paramet er IF_Paramet MHz 433.92 @

⎞
⎟

⎟
⎠

(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 band width by util izing

the appropriate equation (1) or (2) for each crystal
frequency.

The following circuit, Figure 4, is an example of
switched crystal oper ation. The IF Bandwidth Con trol
and REF-OSC Control allow switching between two
operating frequenc ies with either a narro w 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 ad vantage
of this circuit is when a RF interferer is at one
frequency, the recei ver can go to another freque ncy to
get clear reception.

Figure 5 shows PCB layout for MICRF218 with
switched crystal o peration. Please con tact the Micrel
RF Application Group for detailed document.

Dual Frequency Configuration Examples:

Scenario 1:

• Frequency 1 - 315MHz Narrow Bandwidth

• Frequency 2 - 433.92MHz Wide Bandwidth

A 9.81314MHz crystal switched in circuit during
narrow IF mode, combined with a 13.48352MHz
crystal, allows operation at 315MHz with 400kHz IF
bandwidth, and at 433.92MHz with 1500kHz
bandwidth.

Scenario 2:

• Frequency 1 - 315MHz Wide Bandwidth

• Frequency 2 - 433.92MHz Narrow Bandwidth

A 9.78823MHz cr ystal 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:

• Frequency 1 - 315MHz Narrow Bandwidth

• Frequency 2 - 433.92MHz Narrow Bandwidth

A 9.8131MHz crystal switched in circuit, combined
with a 13.51783MHz cr ystal during narrow IF mode,
allows operation at 315MHz with 400kHz IF
bandwidth, and at 433.92MHz with 550kHz
bandwidth.

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L4

J2

RF IN

100nH

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

C2

2.2pF

C3

33pF

REF-OSC CNTR

IF BANDWIDTH
CONTROL

VDD = WIDE BANDWIDTH
0V = NARROW BANDWID TH

L3

100nH

L2

3.9nH

L3

J3

COM

DO

COM

1
2
3
4
5
6
7

ZCB-0603

3.0 to 3.3V

3.0 to 3.3V
SHDN

Figure 4. Dual Frequency QR218BP_SWREF, 315 MHz and 390 MHz

J4

1
2

CON2

+3V

C5

100nF

R3

NP

+3V

NP =Not Placed

J1

1

EXTERNAL REFERE NCE
OSCILLATOR INPUT

2

C1
NP

REFOSC

U1 MICRF218AYQS

1

RO1

2

GNDRF

3

ANT

4

GNDRF

5

VDD

6

IF_BW

7

SEL0

89

SHDN GND

R5
100K

DATA OUT

RO2

NC

RSSI

CAGC

CTH

SEL1

C7

NP

DO

+3V

JPR1

0 OHMS

16
15
14
13
12
11
10

JPR2
NP

R4
0 OHMS

C4

0.047µF

R8
10k

C5

4.7µF

R10
100k

R1
NP

R2
NP

Y1

9.8131MHz

TSDF1220W

Q1

R6
10k

R7
100k

+3V

Y2

12.1287MHz

TSDF1220W

Q2

R11
100k

R9
10k

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Figure 5 Evaluation Board

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Single Crystal Operation for Dual
Frequency Operation

When using a single cr ystal, the IF_BW function m ay
be used to switch between two operating frequencies.

Bandwidth will scale d irectly with operating fr equency
(equation 3). Higher opera t ing f r equency will have the
wider IF bandwidth.

Given one operating frequency, the other frequency
can be determined.:

+

=

* Freq1 Freq2 Bandwidth WideBandwidth Narrow

1.198)(384

2.178)-(384

+

=

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. Filt er BW valu es can be eas ily calcu lated
by direct scaling. See equation below for filter BW
calculation:

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 l ow pass filter can be hardware set by
external pins SEL0 and SEL1.

SEL0 SEL1 Demod BW (@ 434MHz)

0 0 1625Hz
1 0 3250Hz
0 1 6500Hz
1 1 13000Hz - default

Table 1. Demodulation BW Selection

* Freq1 Freq2 Bandwidth NarrowBandwidth Wide

* B BW @433.92MHzFreq Operating W=

433.92

2.178)(384

1.198)-(384

Freq) (Operating

(4)

(5)

(6)

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 vol tage built
up on the CTH capacitor. This threshold is
determined by detecting the positive and negative
peaks of the data signal a nd 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 spik es during this time m ay
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 1.5µA 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 amplif ier to com pensate f or 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 In puts: SEL0 , SEL1, SHDN and
IF_BW.

Reference Oscillator

Figure 6. Reference Oscillator Circuit

The reference oscillator in the MICRF218 (Figure 6)
uses a basic Colpitts crystal oscillator configuration

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with MOS transconductor to provide negative
resistance. All capacitors shown in Figure 6 are
integrated inside the MICRF218. R01 and R02 are
external pins of MICRF218. User only needs to
connect reference oscillation crystal.

See equation (1) and (2) to calculate reference
oscillator crystal frequency for either narrow or wide

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.

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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) off ers a good start for m ost 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 devic e work , which are a crysta l,
Cagc, and Cth capacitors.

The matching network of the he lical PC B antenna ( C9
and L3) can be rem oved and a whip ant enna (ANT2)
or a RF connector (J2) can be us ed instead. Figure 7
shows the entire schem atic of it for 433.9 2MHz. Oth er
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 he lical PCB matc hing network. Tight
tolerance is recomm ended for these devices, like 2%
for the inductor and 0.1pF for the capacitor. PCB
variations ma y require d if f er ent c omponent 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

Products application note.

Freq (MHz) C9 (pF) L3(nH)

315.0

390.0

418.0

433.92

1.2

1.2

1.2

1.5 30

75
43
36

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 atten uate undesired outs ide band noise
which reduces the receiver performance. It is
calculated by the parallel res onanc e equ ati on:

f

=

1

π

C8)*L1*(2

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Table 3 shows the most used frequency values.

Freq (MHz) C8 (pF) L1(nH)

315.0

390.0

418.0

433.92

6.8

6.8

6.0

5.6 24

39
24
24

Table 3. Band-Pass-Filter Front-End Values

There is no need for the b andpass-filter front-end for
applications where it is proven that the outside band
noise does not cause a pr oblem. The MICRF218 h as
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 fr equency outside band no ise, and
the inductor provides addit iona l ESD pr otecti on for the
antenna pin. Two m ethods can be used to find these
values, which are m atched close to 50

Ω. One method

is done by calcul ating the values using the equations
below, and the other m ethod uses a Smith chart. T he
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 m atching values , one needs to know
the input impedanc e of the device.

Table 4 shows the

input impedance of the MICRF218 and suggested
matching values f or the most used frequenc i es . These
suggested values m ay be different if the la yout is not
exactly the same as the one made here.

Freq (MHz) C3 (pF) L2(nH) Z device (Ω)

315.0 1.5 68 16.3 -j210.8

390.0 1.2 47 8.26 – j163.9

418.0 1.2 43 11.1 – j161.9

433.92 1.1 39 9.54 – j152.3

Table 4. Matching values for the most used frequencies

For the frequency of 433.9 2MHz, the inp ut impedanc e
is Z = 9.54 – j152.3
calculated by:

Equivalent parallel = B = 1/Z = 0.410 + j6.54
msiemens

Rp = 1 / Re (B); Xp = 1 / Im (B)
Rp = 2.44k

Ω; Xp = 345.8Ω

Ω. The matching c omponents are

Q = SQRT (Rp/50 + 1)
Q = 7.06
Xm = Rp / Q
Xm = 345.8

Ω

Resonance Method For L-shape Matching Network:
Lc = Xp / (2×Pi×f); Lp = Xm / (2×Pi×f)
L2 = (Lc×Lp) / (Lc + Lp); C3 = 1 / (2×Pi×f×Xm)
L2 = 38.9nH
C3 = 1.06pF
Doing the same calculation example with the Smith

Chart, it would appear as follows,
First, the input impedance of the device is plotted,

(Z = 9.54 – j152)

Ω @ 433.92MHz.(Figure 8).

Figure 8. Device’s Input Impedance, Z = 9.54-j152Ω

Second, the shunt inductor (39nH) and the series
capacitor (1.1pF) f or the desired input impedance ar e
plotted (Figure 9). O ne can see the matching leading
to the center of the Smith Chart or close to 50

Ω.

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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

Ω, -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 (

REFOSC (MHz) Carrier (MHz) HIB Part Numb er

9.813135, NB 315 SA-9.813135-F-10-G-30-30-X

12.149596, NB 390.0 SA-12.149596-F-10-G-30-30-X

13.021874, NB 418.0 SA-13.021874-F-10-G-30-30-X

13.517827, NB 433.92 SA-13.517827-F-10-G-30-30-X

9.788232, WB 315 SA-9.788232-F- 10-G- 30-30-X

12.118764, WB 390.0 SA-12.118764-F-10-G-30-30-X

12.988829, WB 418.0 SA-12.988829-F-10-G-30-30-X

13.483523, WB 433.92 SA-13.483523-F-10-G-30-30-X

Figure 9. Plotting the Shunt Inductor and Series Capacitor

www.hib.com.br).

Table 5. Crystal Frequency and Vendor Part Number

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The oscillator of the MICRF218 is Colpitts in
configuration. It is very sensitive to str ay 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. W hen care is not taken
in the layout, and crystals from other vendors are
used, the oscillator m ay take longer times to start as
well as the time to good d ata in the DO pin to show
up. In some cases, if the stray capacitance is to o high
(> 20pF), the oscillator may not start at all.

Refer to Equations 1 and 2 for crystal frequency
calculations. The local oscillator is low side injection
(32 × 13.51783MHz = 432.571MHz), that is, its
frequency is below the RF carrier frequency and the
image frequency is below the LO frequency. See
Figure 10. The product of the inc oming RF signal a nd
local oscillator sign al will yield the IF f requency, whic h
will be demodulated by the detector of the device.

Figure 10. Low Side Injection Local Oscillator

Narrow and Wide Band Crystal Part Numbers,
WB = IF Wide Band, NB = IF Narrow Band
JP1 and JP2 are the bandwidth selection for the

demodulator bandwidth. To set it correctly, it is
necessary to know the shortest pulse width of the
encoded data sent in the transmitter. Similar to the
example of the data profile in the Figure 11 below,
PW2 is shorter than PW 1, so PW 2 should be used f or
the demodulator ba ndwidth calculati on which is foun d
by 0.65/shortest pulse widt h. 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.

September 2007

SEL0
JP1

Short Short 1625 400 1250
Open Short 3250 200 2500
Short Open 6500 100 5000
Open Open 13000 50 10000

SEL1
JP2

Demod.
BW
(hertz)

Shortest
Pulse
(µsec)

Maximum
baud rate for
50% Duty
Cycle (hertz)

Other frequencies will have different demodulator
bandwidth limits , which are derived fr om the ref erenc e
oscillator frequ ency.
limits for the other two most used frequencies.

Table 6. JP1 and JP2 setting, 433.92 MHz

Table 7 and 8 below shows the

SEL0
JP1

Short Short 1565 416 1204
Open Short 3130 208 2408
Short Open 6261 104 4816
Open Open 12523 52 9633

SEL1
JP2

Demod.
BW

(hertz)

Shortest
Pulse
(µsec)

Maximum
baud rate for
50% Duty
Cycle (hertz)

Table 7. JP1 and JP2 setting, 418.0 MHz

SEL0
JP1

Short Short 1460 445 1123
Open Short 2921 223 2246
Short Open 5842 111 4493
Open Open 11684 56 8987

SEL1
JP2

Demod.
BW

(hertz)

Shortest
Pulse
(µsec)

Maximum
baud rate for
50% Duty
Cycle (Hertz)

Table 8. JP1 and JP2 setting, 390.0 MHz

SEL0
JP1

Short Short 1180 551 908
Open Short 2360 275 1815
Short Open 4720 138 3631
Open Open 9400 69 7230

SEL1
JP2

Demod.
BW

(hertz)

Shortest
Pulse
(µsec)

Maximum
baud rate for
50% Duty
Cycle (Hertz)

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 cap acitors are selected accordin g to
data profile, pulse du ty cycle, dead time bet ween two
received data pack ets, and if the data pattern has or
does not have a preamble. See Figure 11 for an
example of a data profile.

PW1

Preamble

Header

123456 78910

PW2= Narrowest pulsewidth
t1 & t2 =data period

Figure 11. Example of a Data Profile

For best results, the capacitors should always be
optimized for the da ta pattern used. As the baud rate
increases, the capacitor values decrease.
shows suggested values for Manchester Encoded
data, 50% duty cycle.

SEL0
JP1

Short Short 1625 100nF 4.7µF
Open Short 3250 47nF 2.2µF
Short Open 6500 22nF 1µF
Open Open 13000 10nF 0.47µF

SEL1
JP2

Demod.
BW
(hertz)

PW2

t1 t2

Cth
(C6)

Table

Cagc
(Cagc)

determine the signal to noise ratio of the RF link,
crude range estimate f rom 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 energ y.
When its level close to Vdd (SHDN = 1), the de vice is
not in operation. Its DC current consumption is less
than 1µA (do not forget to r em ove R3). W hen toggling
from high to lo w, there will be a tim e required for the
device to come to stead y 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 use d, 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.

Table 10. Suggested Cth and Cagc Values.

Other components used include C5, which is a
decoupling capacit or for the Vdd line; R4 reser ved 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 ca n force a voltage i n 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 m ay 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 worth y of c omm ent. T hey are the
DO, RSSI, and shut down pins. The DO pin has a
driving capabilit y of 0.6mA. This drive current is good
enough for most of the log ic 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

September 2007

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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. Optimi zation 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 connecti on = 1 via or more

vias. Ground plane m ust be soli d and pos sibly witho ut
interruptions. Avoid ground plane on top next to the
matching elements. It normally adds additional stray
capacitance which c hanges the matching. D o not use
phenolic material. Use only FR4 or better materials.
Phenolic material is conductive above 200MHz. RF
path should be as straight as pos sible 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 poss ible
from the RF circuits. Avoi d thick traces , the higher the
frequency, the thinn er the trace should be in order to
minimize losses in the RF path.

September 2007

Figure 14. QR218HE1 Top Layer.

Figure15. QR218HE1 Bottom Layer, Mirror Image.

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Figure 16. QR218HE1 Top Silkscreen Layer.

Figure 17. QR218HE1 Dimensions.

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QR218HE1 Bill of Materials, 433.92 MHz

Item Part Number Manufacturer Description Qty.

ANT1 Helical PCB Antenna Pattern 1
ANT2 (np)50-ohm Ant 168mm 20 AWG, rigid wire 0

C9 MuRata 1.5pF , 0402/0603 1
C4 Murata / Vishay 4.7µF, 0805 1
C3 Murata/Vishay 1.1pF, 0402/0603

C6,C5 Murata / Vishay 0.1µF, 0402/0603 2

C8 Murata 5.6pF, 0402/0603 1

JP1,JP

2, JP3

JP4 (np) not placed 0

J2 (np) not placed 0
J3 CON6 1
L1 Coilcraft / Murata /

L2 Coilcraft / Murata /

L3 Coilcraft / Murata /

R1,R2,

R4
R3 Vishay 100kΩ , 0402 1
Y1 HCM49

Y1A HC49/US

U1 MICRF218AYQS Micrel Semiconductor QSOP16 1

Notes:

1. On Semiconductor Tel: [phone]

2. Micro Commercial Corp. Tel: [phone]

3. Sumida Tel: [phone]

4. Murata Tel: [phone]

5. Vishay Tel: [phone]

6. Micrel S emiconduc tor Tel: [phone]

Vishay short, 0402, 0Ω resistor 2

24nH 5%, 0402/0603 1

ACT1

39nH 5%, 0402/0603 1

ACT1

30nH 2%, 0402/0603 1

ACT1

(np) 0402, not placed 0

www.hib.com.br
www.hib.com.br

Table 11. QR218HE1 Bill of Materials, 433.92 MHz, Narrow Band.

(np)13.51783MHz Crystal 0

13.51783MHz Crystal 1

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Package Information

QSOP16 Package Type (AQS16)

MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL [phone] FAX [phone] 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

Micrel Products are not designed or authorized for use as components in life support appliances, devices or syst ems where malfu nction of a

product can reasonably be expected to result in personal injury. Life support devices or s yst ems 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

September 2007

its use. Micrel reserves the right to change circuitry and specifications at any time without not if ication to the customer.

and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale.

© 2007 Micrel, Incorporated.

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Revision History
Date Edits by: Revision Number

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