Rainbow Electronics U2741B User Manual

Features

• Very High Transmitting Frequency Accuracy Compared to SAW Solutions

(Enables Receivers at Lower Bandwidth than with SAW Resonators)

• Lower Cost than the Usual Discrete Solutions Using SAW and Transistors

• Supply Voltage 2.0 V to 5.5 V in the Temperature Range -20°C to 70°C

Supply Voltage 2.2 V to 5.5 V in the Temperature Range -40°C to 85°C

• XTO Output for Clocking the Microcontroller, Thereby Together with the ATAR090 or

ATAR890 Results in the Optimum System Cost-effectiveness

• One-chip Solution with Minimum External Circuitry

• Very Small SSO16 Package, Pitch 0.635, 150 mil

• “Single-ended Open-collector” Output (Same Antennas as in Discrete Solutions Can

Be Used, Simpler Adaptation of Magnetic Loop Antennas)

• Very Large FSK Frequency Deviation Achievable by ±100 ppm Pulling of the Reference

Crystal

• Enables Receivers at Lower Bandwidth than with SAW Resonators

• ESD Protection According to MIL-STD.883 (4 KV HBM) Except Pins XTO1/ 2,

ANT and LF

Electrostatic sensitive device.
Observe precautions for handling.

Description

UHF ASK/FSK
Transmitter

U2741B

The U2741B is a PLL transmitter IC which has been especially developed for the
demands of RF low-cost data transmission systems at data rates up to 20 kBaud.

The transmitting frequency range is 300 MHz to 450 MHz. The device can be used in
both FSK and ASK systems.

Rev. 4733A–RKE–11/03

Figure 1. System Block Diagram

1 Li cell

Encoder

ATARx9x

Keys

Figure 2. Block Diagram

UHF ASK/FSK

Remote control transmitter

U2741B

PLL

XTO

ASK

FSK

VCC

VCO

Power

amp.

OR

Power

up

Antenna Antenna

UHF ASK/FSK

Remote control receiver

U3741BM

Demod.

IF Amp

LNA VCO

DIVC

PWRSET

PWRVCC

Control

PLL XTO

1...3

controller

Micro-

CLK

GND

LFVCC

LFGND

LF

U2741B

VCO

f

f

PA

ANT

PWRGND1

64

PWRGND2

XTO

n

XTO1

XTO2

2

U2741B

4733A–RKE–11/03

Pin Configuration

Figure 3. Pinning SSO16

U2741B

ASK

1

FSK

VCC

3

CLK

GND

5

LFVCC

LFGND

LF

8

Pin Description

Pin Symbol Function

1 ASK Modulation input ASK
2 FSK Modulation input FSK
3 VCC Supply voltage
4 CLK Clock output
5 GND Ground
6 LFVCC Supply voltage VCO
7 LFGND VCO ground
8 LF Circuit PLL loop

9 XTO2 FM modulation output
10 XTO1 Connection for crystal
11 PWRGND2 Power GND2
12 PWRGND1 Power GND1
13 ANT RF output
14 PWRVCC Supply voltage power amplifier
15 PWRSET Applied to VCC

Pitch factor setting for crystal

16 DIVIC

L: high crystal frequency
H: low crystal frequency

DIVIC

16

2

4

15

14

13

PWRSET

PWRVCC

ANT

U2741B

PWRGND1

12

PWRGND2

6

7

11

10

XTO1

XTO2

9

4733A–RKE–11/03

3

General Description The fully integrated VCO and the “single-ended open-collector” output allow particularly

simple, low-cost RF miniature transmitters to be assembled. The single-ended output
enables a considerably simplified adaptation of both a magnetic loop antenna of any
form or a
would be the case with a differential output.

The XTO's frequency can be selected at either 13.56 MHz (USA 9.844 MHz) or

6.78 MHz (USA 4.9219 MHz). Thus, it is possible to use not only exceptionally small
SMD crystals at 13.56 MHz but also very low-cost 6.78 MHz crystals in a wired metal
package (e.g., in the HC49S housing). The frequency is selected by connecting pin 16
(DIVC) to either GND or V

At high frequencies, crystals have a very fast start-up time (< 1.5 ms at 13.56 MHz,
< 3 ms at 6.78 MHz), whereby a wait time of 5 to 10 ms is required until the transmitter
IC is locked. This means that the processor does not need to poll a lock detect output.

l/4 antenna. This is because the load impedance must not be balanced as

.

S

Functional
Description

The IC can be switched on at both the FSK and the ASK input. The IC's ChipSelect is
performed by the logical OR operation of ASK and FSK input. In the case of V

£ 0.3 V, the power-down supply current is IS

V

ASK

< 0.35 µA. The ASK input activates

off

the power amplifier and the PLL. The FSK input only activates the PLL and, if capacitor

is installed, pulls the crystal to the lower frequency, whereby the transmitter is FSK

C

3

modulated. After switching on at FSK, the VCO locks onto the 32 or 64 times higher fre­quency of the crystal oscillator.

FSK Transmission The U2741B is switched on by V

= VS. 5 ms later, VS is applied to V

FSK

. The output

ASK

can then be modulated by means of pin FSK. This is done by connecting capacitor C
parallel to the load capacitor C

ASK Transmission The U2741B is activated by V

can be modulated by means of pin ASK. In this case, V

is not mounted.

3

Take-over of the Clock
Pulse in the
Microcontroller

sage, the capacitor C

The clock of the crystal oscillator can be used for clocking the microcontroller. The
ATAR090 and ATAR890 have the special feature of starting with an integrated RC oscil­lator to switch on the U2741B with V

4

FSK

.

= VS. V

FSK

remains 0 V for 5 ms, then the output power

ASK

remains = VS during the mes-

FSK

= VS. 5 ms later, the 3.39-MHz clock frequency

is present, so that the message can be sent with crystal accuracy.

Application Circuit The following component values are recommendations for a typical application. C

and C
C
between f = 100 MHz and f = 1 GHz should be as low as possible.

are block capacitors. The values of these capacitors depend on the board layout.

7

=1nF, C6= 1 nF, and C7= 22 nF are typically used here. For C5, the impedance

5

FSK

, C6,

5

,

in

3

is not needed in ASK transmitter applications. In the case of FSK, C3 is selected in

C

3

such a way that the desired transmission frequency deviation is achieved (typical
±30 kHz). The capacitance here depends upon the crystal's load capacity (C
mended by the manufacturer of the crystal. C

C

Loop1

and C

are selected so that the antenna oscillates in resonance and the adap-

Loop2

= 3.9 nF, C1 = 15 nF, and R4 = 220 W.

2

) recom-

4

tation to the appropriate impedance transformation is possible.

is an inductor for the antenna's DC current supply. A typical value is

L

Feed

= 220 nH. L

L

Feed

4

U2741B

can be either printed on the PC board or be a discrete component.

Feed

4733A–RKE–11/03

U2741B

Output Power
Measurement

The output network [as shown in Figure 4] can be used for output power evaluation, the
exact values of L

L

and C10 form the transformation network to adopt the output impedance of the IC to

10

W. Table 1 shows the values for an output power of 2 mW and an R

50

and C10 depend on the layout.

10

PWRSET

= 1.2 kW.

Table 1. Transformation Network

f/MHz C10/pF L10/nH Z

315 2.7 56 260 + j330

433.92 1.8 33 185 + j268

Load_opt

/W

Figure 4. Measurement Output Network

V

S

PWRVCC

L

10

ANT

C

50 W

Z

Load-opt

10

Figure 5. Application Circuit

ASK

FSK

C

CLK

3.39 MHz

7

+VS = 2.0 ... 5.5 V

ASK

OR

FSK

2

LF

3

4

5

6

7

8

Power

up

U2741B

VCO

f

f

64

PA

XTO

n

VCC

CLK

GND

LFVCC

C

6

LFGND

C

R

1

4

C

2

DIVC

161

PWRSET

15

PWRVCC

14

ANT

13

PWRGND1

12

PWRGND2

11

XTO1

10

XTO2
9

R

PWRSET

C

5

13.56 MHz

C

3

Antenna

C

Loop2

L

Feed

C

Loop1

C

4

4733A–RKE–11/03

5

Absolute Maximum Ratings

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Parameters Symbol Min. Max. Unit

Supply voltage V
Power dissipation P
Junction temperature T
Storage temperature T
Ambient temperature T

tot

stg

amb

S

j

-55 125 °C

-40 105 °C

6V
250 mW
150 °C

Thermal Resistance

Parameters Symbol Value Unit

Junction ambient R

thJA

180 K/W

Electrical Characteristics

All parameters are refered to GND (pin 5). The possible operating ranges refer to different circuit conditions:

= 2.0 V to 5.5 V at T

V

S

Parameters Test Conditions Symbol Min. Typ. Max. Unit

Supply current (power down) V
Supply current (power up, output OFF) V
Supply current (power up, output ON) V

Output power

Output power variation for the full
temperature range

Output power variation for
f = 315 MHz compared to
f = 433.92 MHz

Maximum peak output
antenna voltage

Spurious emission

= -20°C to +70°C, VS = 2.2 V to 5.5 V at T

amb

, V

ASK

ASK

ASK

V

= 3 V, T

S

R

PWRSET

R

PWRSET

T

amb

V

= 3.0 V

S

V

= 2.4 V

S

T

amb

V

= 2.0 V

S

P

out

£ 0.3 V, VS < 3.6 V IS

FSK

= GND, V
= VS, VS = 3 V, R

= VS, Vs = 3 V IS

FSK

PWRSET

= 25°C, f = 433.92 MHz

amb

= 1.2 kW
= 1.8 kW

= -40°C to +85°C, f = 433.92 MHz,

= -20°C to +85°C, f = 433.92 MHz,

= P

+ DP

Ref

Ref

f = 315 MHz
P

= P

out

at P

+ DP

Ref

= 2.0 mW,

out

Ref

the load impedance must be selected to
meet the V

maximum requirement

out

the supply current is not dependent on
the load impedance tolerance

= 25°C

at T

amb

f

±(n ´ fPC) where fPC = 6.78 MHz

o

Load capacitance at CLK

£ 3pF

f = 230 MHz to 470 MHz
f < 230 MHz, f > 470 MHz

= -40°C to +85°C (typically 25°C, 3 V)

amb

= 1.2 kW IS

transmit

P
P

DP
DP

DP

DP

V

outmax

Em
Em

Ref
Ref

off

on

Ref
Ref

Ref

Ref

1.5

-0.5

0.35 µA

4.7 6.2 mA
10 12.5 mA

3
1

5
3

-1.5

-4.0

-5.5

dBm
dBm

dB
dB

dB

1.5 dB

VS - 0.7 V V

-40

-58

(peak)

dBC
dBC

6

U2741B

4733A–RKE–11/03

U2741B

Electrical Characteristics (Continued)

All parameters are refered to GND (pin 5). The possible operating ranges refer to different circuit conditions:

= 2.0 V to 5.5 V at T

V

S

Parameters Test Conditions Symbol Min. Typ. Max. Unit

Oscillator frequency XTO

Loop bandwidth

Phase noise PLL

Phase noise VCO

Frequency range of the VCO f
Clock output

(CMOS microcontroller compatible)
Load capacitance at CLK C

Series resonance R of the crystal

FSK modulation frequency rate

ASK modulation frequency rate

CLK output

- Output current Low

- Output current Low

- Output current High

- Output current High
ASK input

- Low level input voltage

- High level input voltage

- Input current High
FSK input

- Low level input voltage

- High level input voltage

- Input current High

= -20°C to +70°C, VS = 2.2 V to 5.5 V at T

amb

M-version: at T

amb

= 25°C
N-version: full temperature range
(monitoring)
Crystal frequency = 13.56 MHz

Crystal frequency = 6.78 MHz

Load capacity of the crystal must be
selected accordingly

For best LO noise
Loop filter components:
C

= 3.9 nF, C1 = 15 nF, R4 = 220 W

2

Referring to the phase comparator
f

= 6.78 MHz

PC

at 1 MHz
at 36 MHz

f

= 13.56 MHz

XTO

f

= 9.84 MHz

XTO

f

= 6.78 MHz

XTO

f

= 4.90 MHz

XTO

Duty cycle of the
modulation signal = 50%

Duty cycle of the
modulation signal = 50%

V

= 0.2 ´ V

CLK

V

CLK

V

CLK

V

CLK

= 0.3 ´ V
= 0.8 ´ V
= 0.7 ´ V

S
S
S
S

= -40°C to +85°C (typically 25°C, 3 V)

amb

f

XTO

13.56 -

13.56

30 ppm

f

XTO

6.78 -

6.78

30 ppm

B

PN

PN
PN

Clk

Loop

VCO
VCO

VCO

CLK

PLL

300 450 MHz

out

100 kHz

-111 -105 dBC/Hz

-91

-123

f

/128 MHz

out

Rs
Rs
Rs
Rs

f

modFSK

f

modASK

I

ol

I

ol

I

oh

I

oh

V

ASKl

V

ASKh

I

ASKh

V

FSKl

V

FSKh

I

FSKh

020kHz

020kHz

150
200

-150

-200 100

1.7

1.7

13.56 +
30 ppm

6.78 +

30 ppm

-87

-119

10 pF

80
100
150
225

0.3

140

0.3

140

MHz

MHz

dBC/Hz

W

µA
µA
µA
µA

V
V

µA

V
V

µA

4733A–RKE–11/03

7

Ordering Information

Extended Type Number Package Remarks

U2741B-NFB SSO16

U2741B-NFBG3 SSO16 Taped and reeled, see above

Tube, optimized power-supply rejection, value of C
differs from M-version, enhanced XTO stability

Package Information

4

8

U2741B

4733A–RKE–11/03

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4733A–RKE–11/03