Micrel MICRF102 Qwikradio uhf ask transmitter Datasheet

MICRF102
Micrel
MICRF102
QwikRadio™ UHF ASK Transmitter
Final Information
General Description
Features
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.
•
•
•
•
•
•
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
Typical Application
+5V
4.7µF
ASK DATA INPUT
MICRF102
RP1
100k
0.1µF
PC
RP2
6.8k
ASK
ANTP
LOOP
ANTENNA
VSS
ANTM
(PCB TRACE)
REFOSC
STBY
VDD
Y1
100k
+5V
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 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
September 2002
1
MICRF102
MICRF102
Micrel
Pin Configuration
PC 1
8 ASK
VDD 2
7 ANTP
VSS 3
6 ANTM
REFOSC 4
5 STBY
MICRF102BM
Pin Description
Pin Number
Pin Name
1
PC
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
connected from VDD to VSS should have the shortest possible path.
4
REFOSC
This is the timing reference frequency which is the transmit frequency
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 Reference Oscillator Section in this data sheet
5
STBY
Input for transmitter stand by control pin is pulled to VDD for transmit
operation and VSS for stand-by mode.
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
MICRF102
Pin Function
Power Control Input. The voltage at this pin should be set between 0.15V to
0.35V for normal operation.
Amplitude Shift Key modulation data input pin. For CW operation, connect
this pin to VDD
2
September 2002
MICRF102
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltage(VDD) ..................................................... +6V
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
Supply Voltage (VDD) .................................... 4.75V to 5.5V
Maximum Supply Ripple Voltage ............................... 10mV
PC Input Range .............................. 150mV < VPC < 350mV
Ambient Operating Temperature (TA) ............ 0°C to +85°C
Programmable Transmitter Frequency Range:
.................................................... 300MHz to 470MHz
Electrical Characteristics
Specifications apply for 4.75V < VDD < 5.5V, VPC = 0.35V, TA = 25°C, freqREFOSC = 12.1875MHz, STBY = VDD. Bold values indicate
0°C ≤ TA ≤ 85°C unless otherwise noted.
Parameter
Condition
Min
Typ
Max
Units
Power Supply
µA
Standby Supply Current, IQ
VSTBY < 0.5V, VASK < 0.5V or VASK > VDD – 0.5V
MARK Supply Current, ION
@315MHz, Note 4
6
10.5
mA
@433MHz, Note 4
8
12
mA
@315MHz
4
6
mA
@433MHz
6
8.5
mA
SPACE Supply Current, IOFF
Mean Operating Current
0.04
33% mark/space ratio at 315MHz, Note 4
4.7
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
@315MHz
tbd
µV/m
@433MHz
tbd
µV/m
RF Output Section and Modulation Limits:
Output Power Level, POUT
Transmitted Power
Harmonics Output, Note 10
@ 315MHz
2nd harm.
3rd harm.
–46
–45
dBc
@433 MHz
2nd harm.
3rd harm.
–50
–41
dBc
40
52
dBc
3
5
Extinction Ratio for ASK
Varactor Tuning Range
Note 7
7
pF
Reference Oscillator Section
Reference Oscillator Input
Impedance
Reference Oscillator Source
Current
Reference Oscillator Input
Voltage (peak to peak)
September 2002
0.2
3
300
kΩ
6
µA
0.5
VPP
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
Time from STBY
Note 9, STDBY transition from LOW to HIGH
Crystal, ESR < 20Ω
6
ms
Transmitter Stabilization Time
from STBY
From External Reference (500mVpp)
10
ms
Crystal, ESR < 20Ω
19
ms
Maximum Data Rate
– ASK modulation
VSTBY
Duty cycle of the modulating signal = 50%
Enable voltage
STBY Sink Current
ASK pin
20
0.75VDD 0.6VDD
ISTBY = VDD
VIH, input high voltage
5
V
6.5
0.75VDD 0.6VDD
VIL, input low voltage
ASK input current
kbits/s
V
0.3VDD 0.25VDD
ASK = 0V, 5.0V input current
–10
0.1
µA
10
V
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 Characteristics 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."
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
tolerances of external components. Guaranteed by design not tested in 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
(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.
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
antenna described in Figure 6.
MICRF102
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September 2002
MICRF102
Micrel
Typical Characteristics
Output Power vs
PC Pin Voltage
Mark Current vs
PC Pin Voltage
25
0
-10
-15
-20
-25
15
10
5
-30
-35
0
September 2002
20
-5
CURRENT (mA)
OUTPUT POWER (dBm)
5
0
0
100 200 300 400 500 600
VPC (mV)
5
100 200 300 400 500 600
VPC (mV)
MICRF102
MICRF102
Micrel
Functional Diagram
Reference
Bias
STBY
VDD
ASK
(10)
TX
Bias
Control
VDD
ANTP
Power
Amp
ANTM
(8)
(9)
Prescaler
Divide
by 32
PC
Buffer
(6a)
(5)
Phase
Detector
Buffer
VCO (4)
(2)
(6b)
(3)
Antenna
Tuning
Control
(7)
Varactor
Device
REF.OSC
Reference
Oscillator (1)
(11)
VSS
Figure 2. MICRF102 Block Diagram
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
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.
6
September 2002
MICRF102
Micrel
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 capacitor for the series capacitance (around 100pF to 220pF) and
use the following formula for the parallel capacitance CT = CP
+ CVAR. The blocking capacitor is needed to ensure that no
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.
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:
LANT = 0.2 × Length × ln(Length/d - 1.6) × 10-9 × k
Where:
Length is the total antenna length in mm.
d is the trace width in mm.
k is a frequency correction factor.
LANT is the approximate antenna inductance in
henries.
Note 1. The total inductance however will be a little greater
than the LANT calculated due to parasitics. A 2nH should be
added to the calculated value. The LANT formula is an
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.
CT =
(4 × π
1
2
× f 2 × L ANT
fTX = 32 × fREFOSC
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 mVP-P and less than 500 mVP-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.
)
Where:
CT total capacitance in farads.
π = 3.1416.
f = carrier frequency in hertz.
LANT inductance of the antenna in henries.
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.
CS =
1
 1

1
 C − (C

 T
VAR + CP ) 
Where:
CVAR is the center varactor capacitance (5pF for the
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
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:
L=
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.
1
4 π 2 f 2C
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.
CS
CVARACTOR
CP
LANTENNA
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.
+5V
ASK DATA INPUT
MICRF102
RP1
(100k)
PC
RP2
(6.8k)
Transformer Output to 50‰
Impedance Transformation
Network
ASK
VDD
ANTP
VSS
ANTM
REFOSC
STBY
To 50‰
Termination of
Spectrum Analyzer
Z2
L
Z1
Z3
ON
OFF
Crystal
Figure 5. Application Test Circuit For Specification Verification
MICRF102
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September 2002
MICRF102
Micrel
Supply Bypassing
Supply bypassing consists of three capacitors; C3 = 4.7uF,
C4 = 0.1uFand C5 = 100pF
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
(MHz) (ohms) (ohms) (nH)
(XL/R)
300
1.7
84.5
44.8
39.72
315
2.34
89.3
45.1
39.65
390
3.2
161
47.4
52.00
434
2.1
136
50.0
78.33
The reference design shown in Figure 6. has an
meeting this requirement.
+5VTX
C5
100pF
50V
C4
0.1 F
16V
0.83
0.85
0.90
0.96
antenna
3
VSS
4
REFOSC
ANTP
7
C3
4.7 F
16V
ANTM
6
SB
5
(Length_mils × 25.4)
1000
d=
(dmils × 25.4)
1000
d = 1.778
 Length

L = 0.2 × Length × ln
− 1.6 × 10 −9 × k
 d

L = 44 × 10 −9
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.
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 × 106
L = 46 × 10-9
CVAR = 5 × 10-12
CP = 12 × 10-12
E-total, phi = 0¡
E-total, phi = 90¡
0.0
30.0
60.0
phi direction
CT =
120.0
l
4 × π × f2 × L
2
C T = 5.55 × 10 −12
120.0
150.0
150.0
CSERIES =
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.
September 2002
VDD
8
Example to Calculate CS and CP
Antenna Inductance Calculation
Length_mils = 2815
dmils = 70
k = 0.85
Figure 6
(180-phi) direction
2
ASK
Figure 8.
Length = 71.501
60.0
PC
MICRF102BM
K
Length =
30.0
1
1
1
1
−
C T C VAR
CSERIES = 8.2 × 10 −12
9
MICRF102
MICRF102
Micrel
MICRF102 Series Capacitor Calculation
f = 433.92 × 106
L = 52 × 10-9
CVAR = 5 × 10-12
CP = 2.7 × 10-12
CT =
1
4 × π2 × f2 × L
C T = 2.587 × 10 −12
CSERIES =
1
1
1
−
C T C VAR + CP
CSERIES = 3.9 × 10 −12
L1 = 52 × 10-9
f1 = 433.92 ¥ 106
C T1 =
1
4 × π 2 × f 2 × L1
C T1 = 2.587 × 10 −12
MICRF102
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September 2002
MICRF102
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
DIMENSIONS:
INCHES (MM)
0.154 (3.90)
0.193 (4.90)
0.050 (1.27) 0.016 (0.40)
TYP
TYP
45°
3°–6°
0.063 (1.60) MAX
0.057 (1.45)
0.049 (1.25)
0.197 (5.0)
0.189 (4.8)
SEATING
PLANE
0.244 (6.20)
0.228 (5.80)
8-Pin SOP (M)
September 2002
11
MICRF102
MICRF102
Micrel
MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
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