Rainbow Electronics AT86RF211 User Manual

Features

• Multiband Transceiver: 400 MHz to 950 MHz

• Monochip RF Solution: Transmitter-Receiver-Synthesizer

• Integrated PLL and VCO: No External Coil

• Very Resistant to Interferers by Design

• Digital Channel Selection

• 200 Hz Steps

• Data Rates up to 64 kbps with Data Clock and no Manchester Encoding Required

• High Output Power Allowing Very Low Cost Printed Antennas:

– +10 dBm in the 915 MHz Frequency Band
– +12 dBm in the 868 MHz Frequency Band
– +14 dBm in the 433 MHz Frequency Band

• FSK Modulation: Integrated Modulator and Demodulator

• Power Savings:

– Stand Alone "Sleep" Mode and "Wake-up" Procedures
– 8 Selectable Digital Levels for Output Power
– High Data Rate and Fast Settling Time of the PLL
– Oscillator Running Mode "Ready to Start"
– Analog FSK Discriminator Allowing Measurement and Correction of Frequency

Drifts

• 100% Digital Interface through R/W Registers Including:

– Digital RSSI
–V

Readout

CC

Description

FSK
Transceiver for
ISM Radio
Applications

AT86RF211
(aka: TRX01)

The AT86RF211 (aka: TRX01) is a single chip transceiver dedicated to low power
wireless applications, optimized for licence-free ISM band operations from 400 MHz to
950 MHz. Its flexibility and unique level of integration make it a natural choice for any
system related to telemetry, remote controls, alarms, radio modems, Automatic Meter
Reading, hand held ter m i na l s, high-tech toys, etc . The AT86RF2 11 makes bidir e c­tional communications affordable for applications such as secured transmissions with
hand-shake procedures, new features and services, etc. The AT86RF211 can easily
be configured to provide the optimal solution for the user’s application: choice of exter­nal filters vs. technical requirements (bandwidth, selectivity, immunity, range, etc), and
software protocol (single channel, multiple channel, FHSS). The AT86RF211 is also
well adapted to battery operated systems, as it can be powered with only 2.4V. It also
offers a “Wake Up” receiver feature to save power by alerting the associated micro­controlleronly when a valid inquiry is detected.

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General Overview

General Overview of Functioning

The AT86RF211 is a microcontroller RF peripheral: all the user has to do is to write/read
registers to setup the chip (i.e. frequency selection) or have information about parame­ters such as RSSI level, Vbattery, PLL lock state. All these operations are carried out via
a three-wire serial interface.

Normal Mode Thechipisset-upbythe microcontroller: frequency and mode (Rx or Tx). Then it acts

like a "pipe": any data entering DATAMSG is immediately radiated (Tx) or any wanted
signal collected by the aerial i s demodulated, transferred to the microcontroller by the
same pin DATAMSG (Rx) as reshaped bits. No data is stored or processed into the
chip. See Figure 1.

Note: In Rx mode, a clock recovery DATACLK is available on the digital interface to provide the

microcontroller with a synchronization signal.

Wake-up Mode The chip is set up in a special Rx mode called sleep mode. The chip wakes up periodi-

cally thanks to its internal timer (stand alone procedure, the microcontroller is in power­down mod e), waiting for an expected message previously defined. If no correct
sequence is received, the periodic scan continues.

If a correct message is detected, its data field is stored into the AT86RF211 (up to 32
bits) and an interrupt is generated on the WAKEUP pin.

See Figure 2 and Figure 3.

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AT86RF211

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Figure 1. Reception and Transmit Mode

SLE, SCK, SDATA

AT86RF211

F = Frequency of
transmitted signal

AT86RF211 (TRX01)

(for set-up)

Transmit mode

3

Companion Microcontroller

SLE, SCK, SDATA

Companion Microcontroller

(for set-up)

3

DATAMSG

AT86RF211 acts like a "pipe"
(data is transmitted with NO
processing): automatic data
to frequency conversion.

- DATAMSG = 0: F = F0

- DATAMSG = 1: F = F1

F = Frequency of
received signal

AT86RF211 (TRX01)

Receive mode

AT86RF211 also acts like a "pipe":
data (collected by the antenna)
is available on pin DATAMSG:

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DATACLK

DATAMSG

DATAMSG

DATACLK

3

Figure 2. Wake-up Overview

Header + Address

Step 1: The chip is set up in sleep mode
using the 3-wire interface (SLE, SCK,
SDATA), then Microcontroller goes to sleep,
waiting for an interrupt on WAKEUP pin

Companion Microcontroller

Figure 3. Periodical Scan

Power

Consumption

Step 2: The chip wakes-up periodically,
waiting for an expected message
(stand-alone operation)

Data stored

3

WAKEUP pin

Data field

AT86RF211 (TRX01)

Wake-up mode

Step 3: If a correct header is received (mandatory)
and address matches (if any), the data field
is then stored into AT86RF211 and WAKEUP pin is
activated (to wake-up the Microcontroller).
The Microcontroller will then read the data into one
of its registers, and begin a relevant procedure.

Note: Data field is optional: the chip can be simply
woken-up with no dedicated data.

Oscillator settling

Sleep mode

Reception mode

Short reception window

Wake Up period

Timing

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AT86RF211

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Block Diagram

Figure 4. AT86RF211 Block Diagram

AT86RF211

Optional

These are the only blocks that depend
on the selected ISM band (433, 868
or 915 MHz): dual band applications
can be done by only switching them.
Synthesizer, loop filter, IF filter(s),
power supply decoupling are identical.

AERIAL

MATCHING

CIRCUIT

TX/RX

PA

RPOWER

PWR
CTRL

RF

FILTER

TX

LNA

GAIN MIN/MAX

Rx

MIXER1

IF1

FILTER

OSC

10.245 MHz
or

20.945 MHz

10.7 MHz
or

21.4 MHz

IF1

MIXER2

AMP

SYNTHESIZER

FREQUENCY

IF2

FILTER

CTRL

CONTROL LOGIC

DATA

MSG

455 kHz

AMP

RSSI LEVEL

DATA

SLE

SCK

CLK

IF2

SDATA

FM DISCRIMINATOR

BANDWIDTH CTRL

DATA SLICER

WAKE-UP

WAKE-UP

OPTIONAL

FILTER

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Pin Description

Table 1. Pinout

Pin Name Comments Pin Name Comments

1 RPOWER Full scale output power resistor 25 SKFILT Threshold for data slicer
2 TXGND1 GND 26 DSIN Data slicer input
3 RF RF input/output 27 DISCOUT Discriminator output
4 TXGND2 GND 28 IF2VCC VCC
5 TXGND3 GND 29 IF2GND GND
6 TXGND4 GND 30 IF2IN IF2 amplifier input
7 TXVCC VCC 31 IF2DEC 2.2 nF to ground
8 TXGND5 GND 32 DISCFILT Discriminator bypass

9 DIGND GND 33 IF2OUT IF2 mixer output
10 DIVCC VCC 34 IF1DEC 4.7 nF to ground
11 DATAMSG Input/output digital message 35 IF1IN IF1amplifierinput
12 SLE Serial interface enable 36 IF1OUT IF1 mixer output
13 SCK Serial interface clock 37 AGND GND
14 SDATA Serial interface data 38 AVCC VCC
15 WAKEUP Wake-up output 39 CVCC2 VCC
16 DATACLK Data clock recovery 40 CGND2 GND
17 – Test pin: do not connect 41 FILT1 Synthesizer output
18 EVCC1 VCC 42 VCOIN Synthesizer input (VCO)
19 EGND1 GND 43 EVCC2 VCC
20 – Test pin: do not connect 44 EGND2 GND
21 CGND1 GND 45 RXIN LNA input from SAW filter
22 CVCC1 VCC 46 RXVCC VCC
23 XTAL1 Crystal input 47 RXGND GND
24 XTAL2 Crystal output 48 SWOUT Switch output

Notes: 1. All VCCpins must be connected in each functional mode (Tx, Rx, wake-up, PDN)

2. To be connected:
Rxmodeonly,allbut:1,3,17,20,48
Tx mode only, all but: 15 to 17, 20, 25 to 27, 30 to 36, 45, 48

3. Pin 20 must remain unconnected or connected to ground

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AT86RF211

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AT86RF211

Detailed Description

Frequency Synthesis

Crystal Reference Oscillator The reference cloc k i s based on a classical Colpitts architecture with three external

capacitors.
An XTAL with load capac itor in the range of 10 pF - 20 pF is recommended. The bias

circuitry of the oscillator is optimized to produce a low drive level for the XTAL. T his
reduces XTAL aging. Any standard, parallel mode 10.245 MHz or 20.945 MHz crystal
canbeused.

Note: The PLL is activated only when the o scillator is stabilized.

Figure 5. Crystal Oscillator Inputs

XTAL1

XTAL2

Figure 6. Typical Networks

(2)

XTAL2

C2 = 56 pF

CL = 20 pF

(1)

33 pF

XTAL1

C1 = 68 pF

6.5/30 pF

XTAL2

C2 = 68 pF

(2)

XTAL1

C1 = 82 pF

CL = 16 pF

Notes: 1. Various load capacitance (CL) crystals can be used. In case CLdiffers of 16 pF or 20 pF, the surrounding network (C1, C2)

2. Thanks to the fine steps of the synthesizer (200 Hz), the trimmer capacitor can be replaced by a software adjustment.

(1)

15 pF

must be re-calculated.

6.5/30 pF

Synthesizer A high-speed, high-resolution multi-loop synthesizer is integrated. The synthesizer can

operate within two frequency bands: 400 MHz to 480 MHz and 800 MHz to 950 MHz. All
channels in these two bands can be selected through software programming (registers
F0 to F3). All circuitry is on-chip with the exception of the PLL loop filter. The phase
comparison is made thanks to a charge pump topology. Typical charge pump current is
225 µA.

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Figure 7. Synthesizer Loop Filter Schematic

P F D

&

C H P

Fref

VCO

FILT1

Note: The PLL loop filter can be designed to optimize the phase noise around the carrier.

Three configurations can be suggested, regarding the application and channel spacing:

- Narrow band: (14.7 kΩ + 2.2 nF) // 220 pF

-Typical:(3.3kΩ + 5.6 nF) // 560 pF

- High datarates: (10 kΩ + 1 nF) // 100 pF

VCOIN

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AT86RF211

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Receiver Description

)

Figure 8. Typical Expected Currents in Rx Mode

32.00

AT86RF211

Supply Current - R x Mode

868 or
915 MHz

30.00

Isupply (mA)

28.00

26.00

2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25

Vsupply (V)

Detailed Current - Rx Mode

10.00

8.00

6.00

4.00

Suppl y Currents (mA

2.00

0.00

2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25

Vsupply (V)

433 MHz

EVCC2

EVCC1
RXVCC

CVCC2
CVCC1

AVCC

DIVCC
IF2VCC
TXVCC

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Overview and Choice of Intermediate Frequencies

For selectivity and flexibility purpose, a classical and robust 2 IF superheterodyne archi­tecture has been selected for the AT86RF211. In order to minimize the external
components cost, the most popular IF values have been chosen. The impedances of the
input/output o f the mixing s tages have been internally matched to the most usual
ceramic filter impedances.

Two typical IF values are suggested:

• 10.7 MHz is the most popular option.

• 21.4 MHz: the image frequency is far enough from the carrier frequency to enable

the use of a front-end ceramic filter instead of a SAW filter. It is also noticeable that

21.4 MHz quartz filters usually have more abrupt slopes than 10.7 MHz ceramic
filters.

Rx - Tx Switch A S PST switch is integrated. In the transmission mode, it protects the LNA input from

the large voltage swings of the PA output (up to several volts peak-to-pea k) , which is
switched to a high impedance state. It is automatically turned ON or OFF by the RX/TX
control bit. The insertion loss is about 2 dB and the reverse isolation about 30 dB i n a
300Ω environment.

Image Rejection and RF Filter The immunity of the AT86RF211 can be improved with an external band-pass filter.

For example, when using a SAW Filter, this device must be matched with the LNA input
and the switch output. The following scheme gives the typical implementation for an
868 MHz application with a 50Ω/50Ω SAW filter.

Figure 9. Typical 50Ω SAW Filter Implementation in the 868 MHz Band

These inductors can be printed

SWOUT (pin 48)

SPST Switch

SAW

50Ω

See Table 2 for precise matching information.
The SAW filter can be replaced by a TEM ceramic, helicoidal or a ceramic coax λ/4 res-

onator designed as a narrow band-pass filter. For instance, with an IF selected at

10.7 MHz, a -3 dB bandwidth of 5 MHz, with an insertion loss of 1 dB and an image
rejection of 12 dB can be achieved with the following:

12 nH2.2 nH

RXIN

(pin 45)

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AT86RF211

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Figure 10. TEM Filter

AT86RF211

1

/4

TEM

pF

1 pF

Zc = 7Ω
l = 0.75
(19 mm)

Such a filter also p rovi des an out-of-band interference reje ction greater than 20dB,
40MHzawayfrom433MHz.

First LNA/Mixer The main characteristics of the LNA/Mixer are typically:

• Voltage gain: 17 dB for the LNA/Mixer; 11 dB if gain min. is selected

• Bandwidth: 1.2 GHz

• Noise figure of LNA alone: 3 dB at 900 MHz, best matching

• Noise figure of LNA + mixer:

8 dB at 900 MHz, with maximum gain and best matching
12 dB at 900 MHz, with minimum gain and best matching

• 1 dB compression point: -20 dBm at the input of LNA

• Matching:

Table 2. Matching Information

Frequency Band RXIN

(1)

SWOUT

(2)

433 MHz 35 + j 170Ω 24 - j 43Ω
868 MHz 37 + j 85Ω 50 - j 42Ω
915 MHz 30 + j 85Ω 50 - j 42Ω

Notes: 1. RXIN: impedance to be seen by LNA input for NF optimization purpose

2. SWOUT: output impedance of the RF switch

The gain is programmable through bit 25 of CTRL1 register (6dB attenuation when min
gain is selected). The choice for the matching between the SWITCH and the LNA
depends main ly on the chosen SAW filter. Usual ly in/out impedance o f SAW filters is
50Ω, but other ones can be implemented and the matching network recalculated thanks
to the previous impedance table.

The LNA is directly coupled to the first mixer. Input and output of the LNA/Mixer must be
connected through a capacitive link because of thei r internal DC coupling. A SAW or
ceramic filter provides such a link.

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Figure 11. Schematic Input of the LNA

Figure 12. Schematic Output of the Mixer

The first mixer translates the input RF signal down to 10.7 MHz or 21.4 MHz as chosen
by the user. The local oscillator is provided by the same synthesizer which will generate
a local frequency 10.7 MHz or 21.4 MHz away from the Tx carrier frequency.

The output impedance of the mixer is 330Ω with a 20% accuracy, so that low cost, stan­dard 10.7 MHz ceramic filters can be directly driven. Other IFs may be chosen thanks to
the high bandwidth (50 MHz) of the mixer.

IF1 filtering A popular ceramic filter is used to reject the second image frequency and provide a first

level of filtering.
The IF1 filter can however be removed; it leads to a sensitivity reduction of about 3 dB

(the substitution coupling capacitor should be > 100 pF).

IF1 Gain and Second Mixer The input impedance of the IF1 amplifier is naturally 330Ω to match the input filter. The

voltage gain, i.e. gain at 10.7 MHz or 21.4 MHz added to the conversion gain at 455 kHz
is typically 14 dB when loaded by 1700Ω. The second mixer operates at a fixed LO fre­quency of 10.245 MHz or 20.945 MHz. Its output impedance is 1700Ω in parallel with 20
pF.

IF1OUT

12

AT86RF211

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Figure 13. IF1 Filtering

IF1

AT86RF211

Filter

IF1OUT
(pin 36)

330 Ω

C > 100 pF

Figure 14. Schematic Input of IF1 Amplifier

IF1IN

IF1DEC

330Ω

IF1IN

(pin 35)

"or"

330 Ω

20 kΩ

Figure 15. Schematic Output of the Second Mixer

1600 Ω

IF2OUT

IF2 Filtering and Gain IF2 filtering achieves a narrow channel selection. In case it is not used, it should be

replaced by a > 1 nF coupling capacitor, thus the IF1 filter is the only part achieving the
channel selection. Available commercial filters with a 35 kHz BW allow data rates up to

19.6 kbps if crystal temperature drifts are very low.
For faste r communications and/or wider channelization, this ceramic filter can be

replaced by an LC band-pass filter as proposed hereafter.

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Figure 16. LC Band-pass Filter

10 nF

Filter

gain

F1

F2

~ F1

40 kHz or higher

~ F2

10 nF

global response

Frequency

• 10 nF capacitors cut DC response forward and backward.

• The first network has the low cut-off frequency.

• The second network has the high cut-off frequency.

IF2 Amplifier Chain The input impedance of the IF2 amplifier is 1700Ω. This value enables the use of popu-

lar filters with impedance between 1500Ω and 2000Ω. It is directly connected to the FSK
demodulator. The bandwidth is internally limited to 1 MHz to minimize the noise before
the discriminator. It acts like a band pass filter centered at 455 kHz with capacitive cou­pling between stages of amplifier and mixer. Total voltage gain is typically 86 dB.
Thanks to the capacitive coupling, no slow DC feedback loop is needed enabling a fast
turn on time. IF2DEC has to be decoupled with at least 2.2 nF.

Figure 17. Input of the IF2 Amplifier Schematic

IF2IN

1900 Ω

14

AT86RF211

IF2DEC

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AT86RF211

RSSI Output The RSSI value can be read as a 6 bits word in the STATUS register. Its value is linear

in dB as plotted below:

Figure 18. Typical RSSI output (board implementation, T = 25°C, V

CC

=3V)

RSSI Output

70

60

50

40

30

RSSI Code

20

10

0

-110 -100 -90 -80 -70 -60 -50 -40 -30

Note: Should the RSSI be required for accuratemeasurement purpose (precision better than 5 dB), then it is possible to measure one

value with a calibrated RF source and store it into the microcontroller, during the production testing.

Di spersi on: +/-5 dB

Dynamic Range: 50dB

Power Level at Antenna Input Port (dBm)

The RSSI dynamic range is 50 dB from -95 dBm to -45 dBm RF input signal power, over
temperature and power supply ranges. The RSSI LSB’s value weighs about 1.3 dB i n
the linear area. The RSSI value is measured from the IF2 chain.

The RSSI is periodically measured thanks to a successive approxi mati on ADC with a
12 µs clock. Thereafter, the time needed to complete the right code depends on the
power step: a 10 dB step on the aerial leads to a 10/1.3 = 8 clock cycles, i.e. 96 µs (full
range from code 0 to 63 = 756 µs). Its value can be compared with a user predefined
value (TRSSI), so that the demodulated data is enabled only if the RSSI value is above
this threshold. Some hysteresis effect may be added (see CTRL1 register’s content).

The AT86RF211 also has the possibility to measure another voltage. The ADC measur­ing the RSSI can be turned into voltage or discriminator output DC level measurement.

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