X
E1201
A
/
XE3005 WH
K
2
Wireless Headset Reference
Design User’s Guide
XE1201A/XE3005-WHK2
Wireless Headset Reference Design
User’s Guide
For further information please contact
XEMICS SA
E-mail: info@xemics.com
Web: http://www.xemics.com/
Cool Solutions for Wireless Connectivity
XEMICS SA • e-mail: info@xemics.com • web: www.xemics.com
X
E1201A WHK02 Wireless
Headset Reference Design
User’s Guide
Table of Contents
1. INTRODUCTION .................................................................................................................................... 3
2. APPLICATION BASICS ........................................................................................................................ 3
3. KIT CONTENTS ..................................................................................................................................... 6
4. DONGLE DEVICE OVERVIEW ............................................................................................................. 7
4.1 RF SIDE ................................................................................................................................................... 7
4.2 AUDIO SIDE .............................................................................................................................................. 7
5. EARPIECE DEVICE OVERVIEW .......................................................................................................... 8
5.1 RF SIDE ................................................................................................................................................... 8
5.2 AUDIO SIDE .............................................................................................................................................. 8
6. SYSTEM OPERATION .......................................................................................................................... 9
6.1 KIT INSTALLATION ..................................................................................................................................... 9
6.2 MAKING A CALL ......................................................................................................................................... 9
6.3 TAKING A CALL.......................................................................................................................................... 9
6.4 VOLUME CONTROL .................................................................................................................................... 9
6.5 MICROPHONE MUTE FUNCTION .................................................................................................................. 9
6.6 CHARGING BATTERIES............................................................................................................................. 10
7. TECHNICAL HINTS............................................................................................................................. 10
7.1 SPECIFICATIONS ..................................................................................................................................... 10
7.1.1 General................................................................................................................................................. 10
7.1.2 RF section ............................................................................................................................................ 11
7.1.3 Audio section ......................................................................................................................................... 11
7.2 DETAILED SCHEMATICS ........................................................................................................................... 12
7.2.1 Power supply ......................................................................................................................................... 12
7.2.2 Dongle controller part ............................................................................................................................ 13
7.2.3 Earpiece controller part ......................................................................................................................... 13
7.2.4 Dongle audio part .................................................................................................................................. 14
7.2.5 Input Level Matching ............................................................................................................................. 14
7.2.6 RF Part XE1201A.................................................................................................................................. 15
7.2.7 Earpiece audio part ............................................................................................................................... 17
7.2.8 Antenna re-matching in plastic housings .............................................................................................. 17
7.3 PHONE CONNECTORS.............................................................................................................................. 18
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1. Introduction
The Wireless Headset Kit (WHK) is based on the XE1201A and XE3005 XEMICS integrated circuits. This WHK
allows the user to be hands free while using their cell phone, without any wire between the headset and the cell
phone. The voice over RF link emulates a full duplex communication, with an audio quality comparable to the
standard wired-line phone network.
The WHK consists of two modules: the headset (user interface) and the dongle (phone interface). Both modules
have a small form-factor, which can be easily integrated in various headset shapes. Thanks to its low current
consumption and robust technology, this design provides a reliable wireless voice link and an extended talk time,
which are key features for portable communication devices.
The following are supported features:
• Emulated full duplex (bi-directional communication).
• ISM license free bands 300-500MHz single frequency.
• Voice quality (phone) transmission.
• Secure communication link (unique ID for both transmitter and receiver).
• Broadcasting range from 3 to 5 meters.
• Current draw 12mA typical, 500µA@3.6V in standby mode.
• Rechargeable battery (power supplied by the cell-phone charger: 4 – 14V)
• Talk time up to 2.5 hours, standby time up to 80 hours with a 40mAh battery.
• Phone calls pick-up.
• Volume control.
• Battery level monitoring.
The XE1201A/XE3005-WHK2 Wireless Headset reference design has been developed to meet European
regulatory requirements. Please note that compliance to the ETSI regulations has to be verified with the final
product and is therefore the responsibility of the final product manufacturer.
2. Application Basics
The goal of this application is to replace the wire of a cell phone hands free kit by a RF link. To get best
performances, reliability and security, a digital communication is used between the cell phone and the headset.
The first step is to convert the analogue phone audio signal to digital audio signal in order to transmit it in digital
format.
The audio signal coming from the phone is a wave signal. Its frequency range is approximately between 300Hz
and 3 kHz. A 4 kHz upper frequency is used here, which means an 8 kHz sampling frequency. As people all have
different voice strength and level, the resolution of the conversion should allow a large dynamic of signal. This can
be achieved by using 16 bits sampling resolution.
To transmit in one way 16bits 8000 times per second, a data rate of 128 kb/s is used. To achieve a pseudo full
duplex operation, the same amount of data has to transmitted in the opposite direction. This feature needs 256
kb/s for data. By using a 16 to 3 compression algorithm, the amount of data transferred is reduced to 48 kb/s. This
reduces the power consumption and enables a longer battery lifetime.
A strong RF protocol achieves a secured link with a perceived full duplex. This protocol builds voice data packets
and includes them in a complete RF frame. The headset microphone signal will be treated as the same way as
the phone signal.
The following diagram shows the different steps to achieve a reliable communication between the cell phone and
the headset.
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From this analysis all the functions described can be implemented on a concrete board. As the power
consumption is the key parameter of the system, the ultra low power XEMICS chips are the best candidates to
realize the different functions.
The AD/DA conversion is processed by the XE3005, XEMICS low power 16 bits conversion audio CODEC. The
XE1201A RF transceiver, which combines low power consumption and high data rate, will be used for RF
transmission and reception. The ADPCM algorithm, communication and RF protocol will be embedded into a
microcontroller.
Both parts of the system (dongle and headset) are based on the same hardware architecture. There is only a
small difference between them due to the audio interface and command buttons. The software also shows small
differences as the headset module acts as the master and the dongle module as the slave.
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RF Part
(Including XE1201A)
RF Rx / Tx
Controller Part
ADPCM Encoder / Decoder
RF Protocol
System Control
Audio Part
(Including XE3005)
ADC / DAC 16bits
8kHz
Frequency Sampling
RX
TX
Control
Loudspeaker Data
Microphone Data
Control
POWER MANAGEMENT
ChargerBattery
Connection for
Headset part
Connection for
dongle part
As described in the previous figure, the device is divided into 4 parts:
• The first is the power management part. It has to be connected to a 3.6V/40mAh battery (this is the main
board power supply). The charge of the battery is realised when connecting a 5.5V power supply through
the jack plug.
• The second part is the microcontroller part. It controls, provides and processes data, it also synchronises
the audio and RF part.
• The RF part provides the Wireless link through the antenna.
• The dongle audio part is connected to the cell phone audio interface while the headset audio part is
connected to a microphone and a loudspeaker. The audio part converts the analogue input signal into
digital data, and converts the digital data into an analogue output signal. The analogue output signal is
single-ended on the dongle device and differential on the headset device.
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3. Kit Contents
1. Programming Socket - This socket allows a developer to reprogram the on-board MSP430
microcontroller.
2. Battery Inhibitors - These inhibitors should be plugged into the on-board battery charger sockets to
prevent the batteries from discharging while the headset is not in use.
3. Nokia Adapter - This adapter should be connected between the phone and the dongle device of the
headset when using it with a Nokia phone.
4. Ericsson Adapter - This adapter should be connected between the phone and the dongle device of
the headset when using it with an Ericsson phone.
5. Batteries - These 3.6V-40mAh batteries supply the necessary power to the system. Each of them
must be connected to the on-board battery sockets.
6. Earpiece Device - Detailed in paragraph 5.
7. Dongle Device - Detailed in paragraph 4.
8. Batteries Charger - When the batteries are connected on the boards, this charger lets the user
charge them both via the on-board charger socket. When plugged, the charger switches the system in
charging mode and inhibits the system’s normal operation.
9. Power Supply Cables For Battery Charger - While in charging mode, one of these cables
(depending on your country) must be plugged between the charger and a high voltage source for
battery charging to proceed.
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4. Dongle Device Overview
4.1 RF side
Loop Antenna
Audio connector
4.2 Audio side
Programming connector
Battery socket
Charger socket
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5. Earpiece Device Overview
5.1 RF side
Speaker
Microphone
5.2 Audio side
Programming connector Charger socket
Pick-up button
Battery socket
Volume up/down buttons
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6. System operation
6.1 Kit Installation
a. Plug one of the batteries into the dongle device corresponding socket.
b. Plug the other battery into the earpiece device corresponding socket.
c. Before first use, it is recommended that the batteries are charged for a few hours. Refer to the “Charging
batteries” section of the document.
d. Connect the audio connector of the dongle device to the cell phone via the correct adapter. (See figures below)
With the Nokia adapter With the Ericsson adapter
e. The two earpiece device LEDs should be off. If it is not the case, put the system in standby mode by pressing
the earpiece device pick-up button. Your Wireless Headset is now in standby mode and ready to operate.
6.2 Making a call
a. From standby mode, press the pick-up button of the earpiece device. Two LEDs on each device now blink at
the same frequency indicating that the RF link is established.
b. Dial the number on your cell phone, then speak normally into the microphone and listen using the earpiece.
c. To end the call and go back to standby mode, press the pick up button three times.
6.3 Taking a call
a. From standby mode, when the phone rings, press the pick-up button of the earpiece device. Two LEDs on each
device now blink at the same frequency indicating that the RF link is established.
b. Speak normally into the microphone and listen using the earpiece.
c. To end the call and go back to standby mode, press the pick up button three times.
6.4 Volume control
During the communication, the user can adjust the volume of the speaker audio flow by pressing the earpiece
device volume buttons as many times as necessary to reach the suitable comfort.
6.5 Microphone mute function
During the communication, the user can mute the microphone by proceeding a long press (>3 seconds) on both
volume buttons. A second LED then blinks rapidly indicating that the muting function is on. Pressing one of the
volume buttons un-mutes the microphone.
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6.6 Charging batteries
To charge the batteries, the power supply cable must be connected to the battery charger. Then, the two low
voltage extremities of the battery charger can be plugged into the charger socket of the pair of devices (earpiece
and dongle). Note that while charging, the system is not functional.
Whenever the system is not intended to be used for a long time, use of the battery inhibitors is recommended to
prevent the batteries from discharging
7. Technical Hints
7.1 Specifications
7.1.1 General
Symbol Specification Min Typ Max Unit Comment
VBAT Battery supply voltage 3.4 3.6 4.5 V NiMh or NiCd *
Vch Charger input voltage 5.0 8 12 V
Tstg Storage temperature -40 85 °C
Top Operating temperature -10 55 °C
Istb Stand-by current 0.5 mA
Iop Operating current 12 mA
Volume
dependent
* For Li-Ion, the battery must include a self-protection circuit.
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7.1.2 RF section
Symbol Specification Min Typ Max Unit Comment
Fout Frequency operation 433.82 433.92 434.02 MHZ
Pout Output power 0 dBm Radiated
Sp1 Spurious emission below
430MHz -54 dBm Radiated
Sp2 Spurious emission
Btw 435 and 1000MHz -36 dBm Radiated
Sp3 Spurious emission
Above 1000MHz -30 dBm Radiated
Sens Input sensitivity -95dBm At input
matching *
Typical antenna gain: -10dBi for a loop or HEMT.
7.1.3 Audio section
Symbol Specification Min Typ Max Unit Comment
Vophone Telephone audio output 1.5 Vpp
Designed for
Nokia. Above,
saturation occurs
Viphone Telephone audio input 50 mVpp
Zear Speaker impedance
25 30 35
Ω
Rdetect Headset detection res 4.2 4.7 5.2 kΩ
Zout Dongle output audio
Impedance 0.7 1
kΩ
Vmic Microphone supply
voltage 1.5 1.6 1.7 V Without load
Rmic Microphone pull-up res
(connected to Vmic) 3 3.3 3.6
kΩ
HPF High-pass cut-off freq 160 200 Hz
LPF Low-pass cut-off freq 3.4kHz kHz
DR Dynamic range 70 80 dB At 1kHz
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7.2 Detailed schematics
7.2.1 Power supply
Figure 1: Power supply
This block uses a 5V regulator to charge the battery across a 100ohm resistor. When the charger jack mono
connector is inserted into the stereo female connector, pins 1 and 2 are shorted and the circuit is turned OFF.
This is an important function because the system can hang when the battery voltage goes below 3.3V. With this, a
clean reset is generated when the charger is removed.
An external POR: MAX 803 with open collector can be mounted (optional). It should not be necessary to do this.
RF caps C2 C3 C5 C36 will shunt to ground any RF signal received by the battery wires or charger; C5 must be
mounted close to the battery connector and C36 close to the 3.3V regulator. Strong RF signals can be “AM
demodulated” by the regulators: the output voltage reduces during GSM frames, which may result in a sound at
160Hz.
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7.2.2 Dongle controller part
Figure 2: Dongle controller part
The controller part includes the micro-controller and all the necessary hardware for it to run properly. The crystal,
some decoupling capacitors, an RC power supply filter (R7 and C1) creates an external POR and a battery
voltage monitoring using R8 R9. 2 LEDs are used for indicating the mode and the system connections.
7.2.3 Earpiece controller part
Same as the dongle, but with 3 additional switches for pickup and volume control.
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7.2.4 Dongle audio part
Figure 3: Dongle audio part
The input filter is a first order band pass filter. High pass function is needed because the phone output DC voltage
could exceed the Vreg 1.6V voltage. Special care has been taken to shunt any RF signal. The output stage of the
CODEC is used as a D class instead of an H class (two outputs in push-pull configuration). The theoretical SNR
and gain reduction is 6dB but in practice the solution is slightly better than a conversion to single-ended with an
OA (limited by the speed and precision of the operational amplifier). The third order low pass filter is made by an
RLC filter. The first 2-pole stage is designed to have an overshoot near the cut-off frequency to compensate the –
3dB of the third pole. The 680uH inductor has a 14 Ω serial parasitic resistance (Q=0.3 at 1 kHz). The package
must be a 1218 form factor; a smaller size will reduce the Q even more. The 3.3u X7R cap is specified with 2.5%
dissipation factor at 1 kHz: 1.2 Ω serial resistor.
The filter is designed to have 32dB attenuation, a low AC output impedance (800Ω) to be less sensitive to the
phone input impedance and a 4.7kΩ DC impedance to be detected as a headset by Nokia phones. The filter has
a 48uA DC current consumption due to R15 which is very low compared to 12mA (no need for an extra cap. In
stand-by mode (V (OUTP) =0). The input reactance is about 280Ω at the PWM output frequency (64 kHz) and the
global filter consumption is mainly determined by losses inside the Rs of the inductor. The pickup function is
realized by the transistor Q3 and the resistor R11. C30, C31 are RF caps.
7.2.5 Input Level Matching
The values of the components are based on the Nokia 8310: 50mVpp max input and 1.5Vpp max phone output. If
the phone output is higher (ex: 3Vpp) R13, R14 and C35 must be adjusted:
Phone max output (Vpp) R13 R14 C35
1 8.2k 3.3k 15n
1.5 10k 2.2k 22n
2 15k 2.2k 22n
3 18k 1.8k 27n
4 18k 1.2k 33n
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How to determine device value:
• Maximum XE3005 input voltage is 270mVpp
• The pole frequency must be between 3.4 and 4.5kHz
7.2.6 RF Part XE1201A
Figure 4: RF part
The RF part is the most critical part of the design, as the matching changes from one layout to another. We
strongly recommend copying the RF part layout as implemented in the Gerber files included in the kit (PCB-
E043V03A.ZIP and PCB-E044V03A.ZIP). If these recommendations are respected, the matching network of the
LNA and PA will be very near to the value indicated in this schematic. But in any case, the schematic of each new
layout will require changes based on RF matching measurements to ensure correct performance.
The LO tank is also a critical part of this block:
• To lower the temperature dependence, the highest capacitance between TKA and TKC because this
dependence is needed due to the temp variation of IO protection devices on TKA TKC. If C18 and C19
are high, L4 L5 will have a low value to oscillate at 434MHz and the global quality factor of the tank will be
high. This configuration can only work if C18 is a trimmer because otherwise the 5% tolerance of caps will
make the oscillator stop.
• To reduce the quality factor of the tank and be able to work with 5% caps and 2% inductors, the cap
needs to be reduced and the inductors increased, which also increases the temperature dependence.
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The compromise here is a rather low cap (1.1p) with two 22n inductor in parallel with an additional degenerating
resistor used to reduce the Q of the tank (the XE1201A has already degenerating resistors inside its oscillator).
For a different RF board, C18 C19 must be adjusted in this way:
1. Short the SAW resonator
2. Measure the tank free-running oscillations with actual C18 C19
3. Calculate Cin + Cboard
4. Deduce from 3 the new C18 C19 value.
5. Verify free-running freq. It should be between 424 and 444MHz.
6. Remove SAW shunt and the OSC is now tuned
Free running tank oscillation frequency is given by:
Freq=1/(2*π*√((L4+L5)*(1/(1/C18+1/C19)+Cboard+Cin)))
L4 and L5 must be equal, C18 C19 can be different and Cboard+Cin is around 1.9pf. The layout is critical: use
short lines and keep symmetry.
This procedure will NOT make the oscillator work at 433.92MHz but near the oscillation frequency of the SAW
(433.92+-0.075). The oscillation frequency will depend on the SAW precision but will be compensated by the
software, by programming the transmitted frequency. The other tank should have the lowest quality factor to
increase the bandwidth and relax component precision: Increase L and reduce C.
4 antennas can be used and matched to 50 Ohms:
1. Microphone wire used as a wire antenna (for earpiece only). Match this antenna with a serial inductor and
a parallel cap.
2. Loop antenna. Match this antenna with a serial cap C27 and a parallel cap.
3. HEMT antenna. No matching if correct antenna.
4. Wire antenna.
The two key parameters for the antenna are:
• Gain
• Directivity
The directivity must be kept as low as possible otherwise there will be a big difference between Min and Max
distance, for example 2m with parallel HEMT antennas and 10m with well aligned HEMT antennas. Here the
HEMT antenna is the smallest antenna but also the most directive, it should not be used at the same time in the
dongle and in the earpiece. A configuration with an HEMT in the dongle and a wire antenna in the earpiece works
well.
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7.2.7 Earpiece audio part
Figure 5: Earpiece audio part
The ear audio part is similar to the dongle audio part. Differences are the following. There is a differential audio
output for driving the speaker, and the microphone wire can be used as an antenna. For that reason the
microphone ground must have a high RF impedance but a low BF impedance. To avoid the ”hamming” low
frequency sound coming either from the xe1201 or from the GSM, the microphone wire must be a coaxial one or a
100pf cap must be soldered directly to the microphone connections. Any RF signal coming inside the microphone
or inside the codec will be AM demodulated and create a 160Hz sound coming from the 6ms frame.
If the microphone is not used as an antenna, replace L12 L13 by 0Ω resistors. 330Ω resistors could replace L12
L13 without too much degradation, but this configuration must be retested on the final board. C28, C30 are SMD
603 size due to their lower parasitic resistance. They have also better performances at these frequencies
(<2GHz).
The output filter is a third order one designed to have 15dB attenuation. The 680uH inductor has a 14 Ω serial
parasitic resistance (Q=0.3 at 1 kHz). The package must be a 1218 one, a smaller size will reduce the Q even
more. The 1.5u X7R cap is specified with 2.5% dissipation factor at 1 kHz: 2.6 Ω serial resistor. A better subjective
audio quality can be achieved by lowering the first pole of the filter (C42 increased to 4,7u). In that case the
transfer function is no longer flat. Comprehension tests must be done with different voices to determine if this is a
satisfactory solution.
The microphone is powered even in sleep mode. This is not a problem because the sleep mode of the earpiece
(master) and dongle (slave) are about the same, so the user will have to charge the battery at the same time.
7.2.8 'Antenna re-matching in plastic housings
The unit as supplied has correctly matched antennae for free-space propagation. Please note that if the units are
enclosed in plastic casing the permeability of the plastic may require that the antennae are re-matched. Please
refer to section 7.2.6 or contact XEMICS for further assistance.
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7.3 Phone connectors
For the demonstration, the kit includes a 2.5mm stereo male jack connector and with 2 adapters: one for Nokia
and the other for Ericsson phones.
The dongle pin B1 is the audio input and must be connected to phone output
The dongle pin B2 must be connected to ground
The dongle pin B3 is the audio output and must be connected to phone input
The dongle pin B4 is a pickup sense line. It must be connected to ground when using the 2.5mm stereo male jack
connector or the Ericsson connector and must be connected to the MIC- pin (see fig) when the Nokia special
connector is used.
If a dedicated connector is used: (see picture below for Ericsson)
Dongle Pin Nokia pin name Ericsson pin number
B1 Audio out + 2
B2 Ground 7 8 10
B3 Audio in + 1
B4 Audio in- / pickup sense 7 8 10 or solder R19
Ericsson pin 7 is used to sense the headset when connected to ground
Ericsson pin 11 is the +5V. It is connected to +Vbat. No additional battery is needed on Ericsson dongles.
Note: Pickup function is not available with Nokia standard adapter.
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(NOKIA 3310 and 8310)
WHK2 GND = B2 and B4
WHK2 audio in = B1
WHK2 audio out = B3
Internal connections
Phone audio in - / pick-up
sense
Phone audio out -
Phone audio in +
Phone audio out +
GROUND
+ 3.3uf capacitor
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WHK2 with standard Ericsson (T28 T29) adapter
Internal connections
WHK2 GND = B2 and B4
WHK2 audio in = B1
WHK2 audio out = B3
WHK2 with dedicated (T28 T29) adapter
WHK2 audio out = B3
WHK2 audio in = B1
WHK2 GND = B2 and B4
+Vbat
1 2 3 4 5 6 7 8 9 10 11
1 2 3 4 5 6 7 8 9 10 11
XEMICS 2002
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presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed
without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor
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