Micrel MICRF102 Final Information

MICRF102 Micrel

MICRF102

QwikRadio™ UHF ASK Transmitter

Final Information

General Description

The MICRF102 is a single chip Transmitter IC for remote
wireless applications. The device employs Micrel’s latest
QwikRadio™ technology. This device is a true “data-in,
antenna-out” monolithic device. All antenna tuning is accom­plished automatically within the IC which eliminates manual
tuning, and reduces production costs. The result is a highly
reliable yet extremely low cost solution for high volume
wireless applications. Because the MICRF102 is a true
single-chip radio transmitter, it is easy to apply, minimizing
design and production costs, and improving time to market.

The MICRF102 uses a novel architecture where the external
loop antenna is tuned to the internal UHF synthesizer. This
transmitter is designed to comply worldwide UHF unlicensed
band intentional radiator regulations. The IC is compatible
with virtually all ASK/OOK (Amplitude Shift Keying/On-Off
Keyed) UHF receiver types from wide-band super-regenera­tive radios to narrow-band, high performance super-hetero­dyne receivers. The transmitter is designed to work with
transmitter data rates from 100 to 20k bits per second.

The automatic tuning in conjunction with the external resistor,
insures that the transmitter output power stays constant for
the life of the battery.

When coupled with Micrel’s family of QwikRadio™ receivers,
the MICRF102 provides the lowest cost and most reliable
remote actuator and RF link system available.

Features

• Complete UHF transmitter on a monolithic chip

• Frequency range 300MHz to 470MHz

• Data rates to 20kbps

• Automatic antenna alignment, no manual adjustment

• Low external part count

• Low standby current <0.04µA

Applications

• Remote Keyless Entry Systems (RKE)

• Remote Fan/Light Control

• Garage Door Opener Transmitters

• Remote Sensor Data Links

Ordering Information

Part Number Temperature Range Package

MICRF102BM –0°C to +85°C 8-Pin SOIC

T ypical Application

+5V

4.7µF

0.1µF

RP1
100k

RP2

6.8k

Y1

MICRF102

PC
VDD

VSS
REFOSC

+5V

ASK

ANTP

ANTM

STBY

100k

Figure 1

QwikRadio is a trademark of Micrel, Inc. The QwikRadio ICs were developed under a partnership agreement with AIT of Orlando, Florida

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com

September 2002 1 MICRF102

ASK DATA INPUT

LOOP

ANTENNA

(PCB TRACE)

MICRF102 Micrel

Pin Configuration

VDD

VSS

REFOSC

Pin Description

Pin Number Pin Name Pin Function

1 PC Power Control Input. The voltage at this pin should be set between 0.15V to

2 VDD Positive power supply input for the IC.
3 VSS This pin is the ground return for the IC. A power supply bypass capacitor

4 REFOSC This is the timing reference frequency which is the transmit frequency

5 STBY Input for transmitter stand by control pin is pulled to VDD for transmit

6 ANTM Negative RF power output to drive the low side of the transmit loop antenna
7 ANTP Positive RF power output to drive the high side of the transmit loop antenna
8 ASK Amplitude Shift Key modulation data input pin. For CW operation, connect

1PC
2
3
4

8 ASK
7

ANTP
ANTM

6

STBY

5

MICRF102BM

0.35V for normal operation.

connected from VDD to VSS should have the shortest possible path.

divided by 32. Connect a crystal (mode dependent) between this pin and
VSS, or drive the input with an AC coupled 0.5Vpp input clock. See

ence Oscillator

operation and VSS for stand-by mode.

this pin to VDD

Section in this data sheet

Refer-

MICRF102 2 September 2002

MICRF102 Micrel

Absolute Maximum Ratings (Note 1)

Supply Voltage(V

Voltage on I/O Pins ............................. VSS–0.3 to VDD+0.3

Storage Temperature Range ..................–65°C to + 150°C

Lead Temperature (soldering, 10 seconds) ........... + 300°C

ESD Rating .............................................................. Note 3

) .....................................................+6V

DD

Operating Ratings (Note 2)

Supply Voltage (V

Maximum Supply Ripple Voltage ...............................10mV

PC Input Range..............................150mV < VPC < 350mV

Ambient Operating Temperature (TA) ............ 0°C to +85°C

Programmable Transmitter Frequency Range:

) .................................... 4.75V to 5.5V

DD

.................................................... 300MHz to 470MHz

Electrical Characteristics

Specifications apply for 4.75V < VDD < 5.5V, VPC = 0.35V, TA = 25°C, freq
0°C ≤ TA ≤ 85°C unless otherwise noted.

Parameter Condition Min Typ Max Units
Power Supply

Standby Supply Current, I
MARK Supply Current, I

SPACE Supply Current, I

Mean Operating Current 33% mark/space ratio at 315MHz, Note 4 4.7 mA

RF Output Section and Modulation Limits:

Output Power Level, P

Transmitted Power @315MHz tbd µV/m

Harmonics Output, Note 10 @ 315MHz 2nd harm. –46 dBc

Extinction Ratio for ASK 40 52 dBc
Varactor Tuning Range Note 7 3 5 7 pF

Reference Oscillator Section

Reference Oscillator Input 300 kΩ
Impedance

Reference Oscillator Source 6 µA
Current

Reference Oscillator Input 0.2 0.5 V
Voltage (peak to peak)

Q

ON

OFF

OUT

V

< 0.5V, V

STBY

@315MHz, Note 4 6 10.5 mA
@433MHz, Note 4 8 12 mA
@315MHz 4 6 mA
@433MHz 6 8.5 mA

33% mark/space ratio at 433MHz, Note 4 6.7 mA

@315MHz; Note 4, Note 5 tbd dBm
@433MHz; Note 4, Note 5 tbd dBm

@433MHz tbd µV/m

@433 MHz 2nd harm. –50 dBc

< 0.5V or V

ASK

ASK

> V

= 12.1875MHz, STBY = VDD. Bold values indicate

REFOSC

– 0.5V 0.04 µA

DD

3rd harm. –45

3rd harm. –41

PP

September 2002 3 MICRF102

MICRF102 Micrel

Parameter Condition Min Typ Max Unit
Digital / Control Section

Calibration Time Note 8, ASK=HIGH 25 ms
Power Amplifier Output Hold Off Note 9, STDBY transition from LOW to HIGH 6 ms

Time from STBY Crystal, ESR < 20Ω
Transmitter Stabilization Time From External Reference (500mVpp) 10 ms

from STBY
Maximum Data Rate

– ASK modulation Duty cycle of the modulating signal = 50% 20 kbits/s

V

STBY

Enable voltage 0.75VDD0.6V
STBY Sink Current I
ASK pin VIH, input high voltage 0.75VDD0.6V

ASK input current ASK = 0V, 5.0V input current –10 0.1 10 µA

Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
Note 4. Supply current and output power are a function of the voltage input on the PC (power control) pin. All specifications in the Electrical Charac-

Note 5. Output power specified into a 50Ω equivalent load using the test circuit in Figure 5.
Note 6. Transmitted power measured 3 meters from the antenna using transmitter board TX102-2A in Figure 6.
Note 7. The Varactor capacitance tuning range indicates the allowable external antenna component variation to maintain tune over normal production

Note 8. When the device is first powered up or it loses power momentarily, it goes into the calibration mode to tune up the transmit antenna.
Note 9. After the release of the STDBY, the device requires an initialization time to settle the REFOSC and the internal PLL. The first MARK state

Note 10. The MICRF102 was tested to be Compliant to Part 15.231 for maximum allowable TX power, when operated in accordance with a loop

teristics table applies for condition VPC = 350mV. Increasing the voltage on the PC pin will increase transmit power and also increase MARK
supply current. Refer to the graphs "Output Power Versus PC Pin Voltage" and "Mark Current Versus PC Pin Voltage."

tolerances of external components. Guaranteed by design not tested in production.

(ASK HIGH) after exit from STDBY needs to be longer than the initialization time. The subsequent low to high transitions will be treated as
data modulation whereby the envelope transition time will apply.

antenna described in Figure 6.

Crystal, ESR < 20Ω 19 ms

DD

V

V
V

DD

STBY

= V

DD

5 6.5 µA

DD

VIL, input low voltage 0.3VDD0.25V

MICRF102 4 September 2002

MICRF102 Micrel

Typical Characteristics

Output Power vs

PC Pin Voltage

5
0

-5

-10

-15

-20

-25

OUTPUT POWER (dBm)

-30

-35

0 100 200 300 400 500 600

VPC (mV)

Mark Current vs

PC Pin Voltage

25

20

15

10

CURRENT (mA)

5

0

0 100 200 300 400 500 600

VPC (mV)

September 2002 5 MICRF102

MICRF102 Micrel

Functional Diagram

STBY

VDD

PC

REF.OSC

VDD

Reference

Oscillator (1)

Reference

Phase

Detector

Bias

(2)

(10)

TX

Bias

Control

Prescaler

Divide

by 32

(5)

(3)

VCO (4)

Figure 2. MICRF102 Block Diagram

(9)

Buffer

Buffer

(6a)

(6b)

Antenna

Tuning

Control

(7)

Power
Amp

(8)

Varactor

Device

(11)

ASK

ANTP
ANTM

VSS

Functional Description

The block diagram illustrates the basic structure of the
MICRF102. Identified in the figure are the principal functional
blocks of the IC, namely the (1, 2, 3, 4, 5) UHF Synthesizer,
(6a/b) Buffer, (7) Antenna tuner, (8) Power amplifier, (9) TX
bias control, (10) Reference bias and (11) Process tuner.

The UHF synthesizer generates the carrier frequency with
quadrature outputs. The in-phase signal (I) is used to drive
the PA and the quadrature signal (Q) is used to compare the
antenna signal phase for antenna tuning purpose.

The Antenna tuner block senses the phase of the transmit
signal at the antenna port and controls the varactor capacitor
to tune the antenna.

The Power control unit senses the antenna signal and con­trols the PA bias current to regulate the antenna signal to the
transmit power.

MICRF102 6 September 2002

The Process tune circuit generates process independent
bias currents for different blocks.

A PCB antenna loop coupled with a resonator and a resistor
divider network are all the components required to construct
a complete UHF transmitter for remote actuation applications
such as automotive keyless entry.

Included within the IC is a differential varactor that serves as
the tuning element to insure that the transmit frequency and
antenna are aligned with the receiver over all supply and
temperature variations.

MICRF102 Micrel

Applications Information

Design Process

The MICRF102 transmitter design process is as follows:

1). Set the transmit frequency by providing the
correct reference oscillator frequency

2). Ensure antenna resonance at the transmit
frequency by:

L

= 0.2 × Length × ln(Length/d - 1.6) × 10-9 × k

ANT

Where:

Length is the total antenna length in mm.
d is the trace width in mm.
k is a frequency correction factor.
L

is the approximate antenna inductance in

ANT

henries.

Note 1. The total inductance however will be a little greater
than the L
added to the calculated value. The L
approximated way to calculate the inductance of the antenna.
The inductance value will vary however, depending on pcb
material, thickness, ground plane, etc. The most precise way
to measure is to use a RF network analyzer.

3). Calculate the total capacitance using the follow­ing equation.

C

Where:

CT total capacitance in farads.
π = 3.1416.
f = carrier frequency in hertz.
L

4). Calculate the parallel and series capacitors,
which will resonate the antenna.

4.1). Ideally for the MICRF102 the series and parallel
capacitors should have the same value or as
close as possible.

4.2). Start with a parallel capacitor value and plug in
the following equation.

C

Where:

C
MICRF102) in farads.

CP is the parallel capacitor in farads.
CS is the series capacitor in farads.

Repeat this calculation until CS and CP are very close and
they can be found as regular 5% commercial values.

Note 2. Ideally, the antenna size should not be larger than the
one shown here. The bigger the antenna area, the higher the
loaded Q in the antenna circuit will be. This will make more

calculated due to parasitics. A 2nH should be

ANT

=

T

4

()

inductance of the antenna in henries.

ANT

=

S




CC C



is the center varactor capacitance (5pF for the

VAR

1

22

ππ

fL

×××

ANT

1

11

−

()

T VAR P




+



formula is an

ANT

difficult to match the parallel and series capacitors. Another
point to take into consideration is the total ac rms current
going through the internal varactor in the MICRF102. This
current should not exceed 16mA rms. The parallel capacitor
will absorb part of this current if the antenna dimensions are
appropriate and not exaggerated larger than the one shown
here.

Note 3. A strong indication that the right capacitor values
have been selected is the mean current with a 1kHz signal in
the ASK pin. Refer to the

Electrical Characteristics

for the

current values.
Note 4. For much smaller antennas, place a blocking capaci-

tor for the series capacitance (around 100pF to 220pF) and
use the following formula for the parallel capacitance CT = C
+ C

. The blocking capacitor is needed to ensure that no

VAR

dc current flows from one antenna pin to the other.

5.) Set PC pin to the desired transmit power.

Reference Oscillator Selection

An external reference oscillator is required to set the transmit
frequency. The transmit frequency will be 32 times the
reference oscillator frequency.

ff

=×32

TX

REFOSC

Crystals or a signal generator can be used. Correct reference
oscillator selection is critical to ensure operation. Crystals
must be selected with an ESR of 20 Ohms or less. If a signal
generator is used, the input amplitude must be greater than
200 mV

and less than 500 mV

P-P

P-P

.

Antenna Considerations

The MICRF102 is designed specifically to drive a loop an­tenna. It has a differential output designed to drive an induc­tive load. The output stage of the MICRF102 includes a
varactor that is automatically tuned to the inductance of the
antenna to ensure resonance at the transmit frequency.

A high-Q loop antenna should be accurately designed to set
the center frequency of the resonant circuit at the desired
transmit frequency. Any deviation from the desired frequency
will reduce the transmitted power. The loop itself is an
inductive element. The inductance of a typical PCB-trace
antenna is determined by the size of the loop, the width of the
antenna traces, PCB thickness and location of the ground
plane. The tolerance of the inductance is set by the manufac­turing tolerances and will vary depending how the PCB is
manufactured.

The MICRF102 features automatic tuning. The MICRF102
automatically tunes itself to the antenna, eradicating the need
for manual tuning in production. It also dynamically adapts to
changes in impedance in operation and compensates for the
hand-effect.

Automatic Antenna Tuning

The output stage of the MICRF102 consists of a variable
capacitor (varactor) with a nominal value of 5.0pF tunable
over a range from 3pF to 7pF. The MICRF102 monitors the
phase of the signal on the output of the power amplifier and
automatically tunes the resonant circuit by setting the varactor
value at the correct capacitance to achieve resonance.

P

September 2002 7 MICRF102

MICRF102 Micrel

In the simplest implementation, the inductance of the loop
antenna should be chosen such that the nominal value is
resonant at 5pF, the nominal mid-range value of the MICRF102
output stage varactor.

Using the equation:

1

LfC=

22

4

ππ

If the inductance of the antenna cannot be set at the nominal
value determined by the above equation, a capacitor can be
added in parallel or series with the antenna. In this case, the
varactor internal to the MICRF102 acts to trim the total
capacitance value.

C

S

C

VARACTOR

C

P

L

ANTENNA

Figure 4.

Supply Bypassing

Correct supply bypassing is essential. A 4.7uF capacitor in
parallel with a 100pF capacitor is recommended.

The MICRF102 is susceptible to supply-line ripple, if supply
regulation is poor or bypassing is inadequate, spurs will be
evident in the transmit spectrum.

Transmit Power

The transmit power specified in this datasheet is normalized
to a 50Ohm load. The antenna efficiency will determine the
actual radiated power. Good antenna design will yield trans­mit power in the range of 67dBµV/m to 80dBµV/m at 3 meters.

The PC pin on the MICRF102 is used to set the transmit
power. The differential voltage on the output of the PA (power
amplifier) is proportional to the voltage at the PC pin.

With more than 0.35V on the PC pin the output amplifier
becomes current limited. At this point, further increase in the
PC pin voltage will not increase the RF output power in the
antenna pins. Low power consumption is achieved by de­creasing the voltage in the PC pin, also reducing the RF
output power and maximum range.

Output Blanking

When the device is first powered up or after a momentary loss
of power the output is automatically blanked (disabled). This
feature ensures RF transmission only occurs under con­trolled conditions when the synthesizer is fully operational,
preventing unintentional transmission at an undesired fre­quency. Output blanking is key to guaranteeing compliance
with UHF regulations by ensuring transmission only occurs in
the intended frequency band.

+5V

RP1
(100k)

RP2
(6.8k)

Transformer Output to 50‰
Impedance Transformation

Network

Z2

Z1 Z3

Crystal

MICRF102

PC
VDD

VSS
REFOSC

ASK

ANTP

ANTM

STBY

ASK DATA INPUT

L

ON
OFF

Figure 5. Application Test Circuit For Specification Verification

To 50‰

Termination of

Spectrum Analyzer

MICRF102 8 September 2002

MICRF102 Micrel

C

CC

C

SERIES

T VAR

SERIES

=

−

=×

−

1

11

82 10

12

.

Design Examples

Complete reference designs including gerber files can be
downloaded from Micrel’s website at www.micrel.com/prod­uct-info/qwikradio.shtml.

Antenna Characteristics

In this design, the desired loop inductance value is deter­mined according to the table below.

Freq. R XL Ind Q K

(MHz) (ohms) (ohms) (nH) (XL/R)

300 1.7 84.5 44.8 39.72 0.83
315 2.34 89.3 45.1 39.65 0.85
390 3.2 161 47.4 52.00 0.90
434 2.1 136 50.0 78.33 0.96

The reference design shown in Figure 6. has an antenna
meeting this requirement.

Supply Bypassing

Supply bypassing consists of three capacitors; C3 = 4.7uF,
C4 = 0.1uFand C5 = 100pF

+5VTX

C4

0.1 F
16V

C5
100pF
50V

C3

4.7 F
16V

PC1

VDD

2

V

3

SS

MICRF102BM

ASK 8

ANTP 7

ANTM 6

SB 5REFOSC4

Figure 8.

Example to Calculate CS and C

P

Antenna Inductance Calculation

Length_mils = 2815
dmils = 70
k = 0.85

dmils

×

Length_mils 25.4

Length
Length 71.501

()

=
=

1000

×

()

d

=

d

=

1 778..

25 4

1000

Figure 6

Loop antennas are often considered highly directional. In fact
small loop antennas can achieve transmit patterns close in
performance to a Dipole antenna. The radiation pattern
below is the theoretical radiation pattern for the antenna
shown in Figure 6.

E-total, phi = 0¡

E-total, phi = 90¡

30.0

60.0

(180-phi) direction

120.0

150.0

0.0

30.0

60.0

phi direction

120.0

150.0

180.0

Figure 7. Polar Elevation pattern at 315MHz

The 0 degree plot is the radiation pattern in the plane of the
transmitter PCB, the 90 degree plot represents the plane
perpendicular to the PCB. Micrel’s evaluation of the perfor­mance of the board in Figure 6. indicates an even more
uniform radiation pattern that the theoretical plot shown here.

Length

L 0.2 Length ln

=× × −

9

=×

L4410

−






d



9

−

××

1.6 10 k





Where Length and d are in mm and L is in H;
Where k is a constant dependent on pcb material, copper

thickness, etc

MICRF102 Series Capacitor Calculation

f = 315 × 10
L = 46 × 10
C

VAR

CP = 12 × 10

C

=

T

C

=×

T

6

-9

= 5 × 10

-12

-12

l

22

fL

×××

4

ππ

.

555 10

−

12

September 2002 9 MICRF102

MICRF102 Micrel

MICRF102 Series Capacitor Calculation

f = 433.92 × 10
L = 52 × 10
C

= 5 × 10

VAR

CP = 2.7 × 10

6

-9

-12

-12

C

=

T

C

=×

T

C

SERIES

C

SERIES

L1 = 52 × 10
f1 = 433.92 ¥ 10

C

=

TT1

C

=×

1

1

22

fL

×××

ππ

4

−

.

2 587 10

=

=×

12

11

−

CC C

T VAR P

39 10

.

-9
6

1

22

fL

ππ

41

×××

−

.

2 587 10

12

1

+

−

12

MICRF102 10 September 2002

MICRF102 Micrel

Package Information

0.026 (0.65)
MAX)

PIN 1

0.154 (3.90)

0.050 (1.27)

0.057 (1.45)

0.049 (1.25)

TYP

0.016 (0.40)
TYP

0.197 (5.0)

0.189 (4.8)

0.063 (1.60) MAX

SEATING

PLANE

8-Pin SOP (M)

DIMENSIONS:

INCHES (MM)

0.193 (4.90)

0.244 (6.20)

0.228 (5.80)

45°

3°–6°

September 2002 11 MICRF102

MICRF102 Micrel

MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 [phone] FAX + 1 [phone] WEB http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel, Inc.

© 2002 Micrel, Incorporated

MICRF102 12 September 2002