MICRF104BMTR - Micrel - Product.Network

November 8, 2001 1 MICRF104

MICRF104 Micrel

MICRF104

1.8V, QwikRadio™ UHF ASK Transmitter

Final Information

General Description

The MICRF104 is a low voltage Transmitter IC for remote

wireless applications. The device employs Micrel’s latest

QwikRadio™ technology. This device is a true “data-in,

antenna-out” 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. The MICRF104 incorporates a DC/DC con-

verter to boost the input voltage up to 5V for the RF portion of

the IC. This feature enables the MICRF104 to operate off

supply voltages as low as 1.8V and transmit at power in

excess of –2dBm.

The MICRF104 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-regenera-

tive radios to narrow-band, high performance super-hetero-

dyne 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 MICRF104 provides the lowest cost and most reliable

remote actuator and RF link system available.

T ypical Application

VDDPWR

VSS

REFOSC

VSS

MICRF104

DATA IN

0.1µF 100pF 10µF

10µF

22µH

141

VSS

RFSTBY

VDDRF

ASK

ANTM ANTP

Power

Control

RF Standby

1.8V to 4V

Supply

LOOP

ANTENNA

(PCB TRACE)

Figure 1

Features

•Complete UHF transmitter on a chip

•Frequency range 300MHz to 470MHz

•Data rates to 20kbps

•Automatic antenna alignment, no manual adjustment

•Low external part count

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

MICRF104BM 0°C to +85°C 14-Pin SOIC

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com

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

MICRF104 Micrel

MICRF104 2 November 8, 2001

Pin Description

Pin Number Pin Name Pin Function

1 VDDPWR Positive power supply input for the DC/DC converter.

2, 4, 13 VSS Ground return

3 5V 5V Output from the DC / DC converter

5 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

Refer-

ence Oscillator

Section in this data sheet

6 RFSTBY Input for transmitter standby control pin is pulled to VDDRF for transmit

operation and VSS for stand-by mode.

7 ANTM Negative RF power output to drive the low side of the transmit loop antenna

8 ANTP Positive RF power output to drive the high side of the transmit loop antenna

9 ASK Amplitude Shift Key modulation data input pin.

10 VDDRF Positive power supply input for the RF circuit. A power supply bypass

capacitor connected from VDDRF to VSS should have the shortest possible

path.

11 PC Power Control Input. The voltage at this pin should be set between 0.3V to

0.4V for normal operation.

12 SW DC/DC converter Switch. NPN output switch transistor collector.

14 EN Chip Enable input. Active high

Pin Configuration

1VDDPWR

VSS

REFOSC

RFSTBY

ANTM

14 EN

VSS

VDDRF

ASK

ANTP

MICRF104BM

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MICRF104 Micrel

Electrical Characteristics

Specifications apply for VDDPWR = 1.8V, VPC = 0.35V, freqREFOSC = 12.1875MHz, RFSTBY = VDDRF, EN = VDDPWR.

TA = 25°C, bold values indicate 0°C ≤ TA ≤ 85°C unless otherwise noted.

Parameter Condition Min Typ Max Units

Power Supply

Shutdown current, IVDDPWR EN = RFSTBY = VSS 50 µA

RF Standby supply, IVDDPWR RFSTBY = VSS, EN = VDDPWR 1.5 mA

RF Standby supply, IVDDPWR RFSTBY = VSS, EN = VDDPWR = 4V 0.6 mA

MARK supply current, ION Note 4, 31 41 mA

Note 4, VDDPWR = 4V 12 17 mA

SPACE supply current, IOFF 22 30 mA

VDDPWR = 4V 9 12 mA

Mean operating current 33% mark/space ratio, Note 4 25 34 mA

33% mark/space ratio, VDDRWR = 4V, Note 4 10 14 mA

5V Max. output current 15 mA

Note 9, VDDPWR = 4V 35 mA

5V Output Voltage range Note 9 4.75 5.25 V

RF Output Section and Modulation Limits:

Output power level, POUT @315MHz; Note 4, Note 5 –2 dBm

@433MHz; Note 4, Note 5 –2.5 dBm

Transmitted Power @315MHz tbd µV/m

@433MHz tbd µV/m

Harmonics output @ 315MHz 2nd harm. –46 dBc

3rd harm. –45

@433 MHz 2nd harm. –50 dBc

3rd harm. –41

Extinction ratio for ASK 40 52 dBc

Varactor tuning range Note 7 5 6.5 8pF

Reference Oscillator Section

Reference Oscillator Input 300 kΩ

Impedance

Reference Oscillator Source 6µA

Current

Reference Oscillator Input 0.2 0.5 VPP

Voltage (peak to peak)

Absolute Maximum Ratings (Note 1)

Supply Voltage(VDDPWR, VDDRF)..................................+6V

Voltage on I/O Pin EN .................................................. [tbd]

Voltage on I/O Pins, RFSTBY, ASK, PC, ANTP, ANTM

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

Operating Ratings (Note 2)

Supply Voltage (VDDPWR) .................................. 1.8V to 4V

PC Input Range..................................0.15V < VPC < 0.35V

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

Programmable Transmitter Frequency Range: 300MHz to

470MHz

MICRF104 Micrel

MICRF104 4 November 8, 2001

Parameter Condition Min Typ Max Units

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 Crystal, ESR < 20Ω19 ms

Maximum Data rate

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

VRFSTBY Enable Voltage

0.75V

DDRF

0.6V

DDRF

STBY Sink Current 56.5 µA

VEN Enable Voltage High

0.95V

DDPWR

Low 0.3 V

EN pin current –10 10 µA

ASK pin VIH, input high voltage

0.8V

DDRF

VIL, input low voltage

0.2V

DDRF

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-

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."

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.

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MICRF104 Micrel

0 100 200 300 400 500 600

CURRENT (mA)

(mV)

Mark Current vs

PC Pin Volta

-35

-30

-25

-20

-15

-10

-5

0 100 200 300 400 500 600

OUTPUT POWER (dBm)

VPC (mV)

Output Power vs

PC Pin Volta

Typical Characteristics

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MICRF104 6 November 8, 2001

Functional Description

The block diagram illustrates the basic structure of the RF

portion of the MICRF104. 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.

Functional Diagram

Bias

Control

Varactor

Device

Antenna

Tuning

Control

Power

Amp

Buffer

VSS

ANTM

ANTP

ASK

Buffer

Prescaler

Divide

by 32

RF Transmitter

REF.OSC

VDDRF

VDD (10)

(5)

(2)

Reference

Oscillator (1)

VCO (4)

(3)

(9) (8)

(7)

(11)

(6a)

(6b)

STBY Reference

Bias

Phase

Detector

VSS

VDDPWR

EN Enable

Thermal

Shutdown

Logic Driver

Bandgap

Reference

DC/DC Converter

Error

Amplifier

1.2V

Oscillator

Figure 2. MICRF104 Block Diagram (RF Circuit)

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 con-

trols the PA bias current to regulate the antenna signal to the

transmit power.

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

November 8, 2001 7 MICRF104

MICRF104 Micrel

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.

MICRF104 Micrel

MICRF104 8 November 8, 2001

Applications Information

Design Process

The MICRF104 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:

a. Either, matching antenna inductance to the

center of the tuning range of the internal

varactor.

b. Or, matching capacitance with the antenna

inductance by adding an external capacitor (in

series with, or in parallel with, the internal

varactor)

3). Set PC pin for 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.

TX REFOSC

=×32

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 MICRF104 is designed specifically to drive a loop an-

tenna. It has a differential output designed to drive an induc-

tive load. The output stage of the MICRF104 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 manufac-

turing tolerances and will vary depending how the PCB is

manufactured.

In the simplest implementation a single capacitor in parallel

with the antenna will provide the desired resonant circuit.

ANTENNA

Figure 3.

The resonant frequency is determined by the equation:

fCL

ππ

The tolerance in the antenna inductance combined with the

tolerance of the capacitor in parallel with it will result in

significant differences in resonant frequency from one trans-

mitter to another. Many conventional loop antenna transmit-

ters use a variable capacitor for manual tuning of the resonant

circuit in production. Manual tuning increases cost and re-

duces reliability.

A capacitor correctly tuned during manufacture may drift over

time and temperature. A change in capacitance will alter the

resonant frequency and reduce radiated power. In addition,

a hand close to the antenna will alter the resonant properties

of the antenna and de-tune it.

The MICRF104 features automatic tuning. The MICRF104

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 MICRF104 consists of a variable

capacitor (varactor) with a nominal value of 6.5pF tunable

over a range from 5pF to 8pF. The MICRF104 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.

In the simplest implementation, the inductance of the loop

antenna should be chosen such that the nominal value is

resonant at 6.5pF, the nominal mid-range value of the

MICRF104 output stage varactor.

Using the equation:

LfC

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 MICRF104 acts to trim the total

capacitance value.

ANTENNA

VARACTOR

EXTERNAL

Figure 4.

Starting with the inductance of the antenna the capacitance

value required to achieve resonance can be calculated.

For example a 315MHz transmitter with a 45.1nH inductance

antenna will require no capacitor in parallel with the antenna,

only the internal varactor that will be tuned to 5.66pF, which

is very close to mid range and can be determined using the

equation:

CfL

ππ

Where:

f = 315Mhz

November 8, 2001 9 MICRF104

MICRF104 Micrel

L = 45.1nH

The value of the capacitor is calculated as 5.66pF.

Supply Bypassing

Correct supply bypassing is essential. A 4.7uF capacitor in

parallel with a 100pF capacitor is required and an additional

0.1µF capacitor in parallel is recommended.

The MICRF104 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 trans-

mit power in the range of 67dBµV/m to 80dBµV/m at 3 meters.

The PC pin on the MICRF104 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.

If the PC pin voltage rises above 0.4 V the output power

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 de-

creasing 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 con-

trolled conditions when the synthesizer is fully operational,

preventing unintentional transmission at an undesired fre-

quency. Output blanking is key to guaranteeing compliance

with UHF regulations by ensuring transmission only occurs in

the intended frequency band.

MICRF104 Micrel

MICRF104 10 November 8, 2001

Package Information

45°3°–6°

0.244 (6.20)

0.228 (5.80)

0.344 (8.75)

0.337 (8.55)

0.006 (0.15)

SEATING

PLANE

0.026 (0.65)

MAX)0.016 (0.40)

TYP

0.154 (3.90)

0.057 (1.45)

0.049 (1.25)

0.193 (4.90)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

14-Pin SOIC (M)

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

TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 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.