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AS3911 general purpose demo Hardware description

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austriamicrosystems AG  
is now  
ams AG  
The technical content of this austriamicrosystems application note is still valid.  
Contact information:  
Headquarters:  
ams AG  
Tobelbaderstrasse 30  
8141 Unterpremstaetten, Austria  
Tel: +43 (0) 3136 500 0  
e-Mail:
Please visit our website at www.ams.com  
AS3911  
AS3911 general purpose demo  
Hardware description  
Application noe  
Rev 1V00 December 2011  
Application engineer: Thomas Luecker  
MarketinManager: Mark Dickson  
Proprietary and Confidential  
1
1
2
3
3.1  
3.2  
3.3  
Disclaimer............................................................................................................ 2  
Introduction.......................................................................................................... 3  
Hardware............................................................................................................. 4  
Block diagram.........................................................................................................4  
EMC and Power supply concept..............................................................................5  
Digital section ( micro controller) ...........................................................................6  
3.3.1 Programming header P1 ....................................................................................6  
Analog section ........................................................................................................7  
3.4.1 Power concept...................................................................................................8  
3.4.2 Antenna stage....................................................................................................
3.4.3 Capacitive wakeup ............................................................................................9  
Measurement ..................................................................................................... 9  
Current consumption..............................................................................................9  
Antenna stage........................................................................................................9  
Measurement of the antenna Parameters.............................................................9  
Determination of the Antenna resistor................................................................10  
Matching of the driver......................................................................................11  
Verification of the Q factor in the timomain ..................................................12  
Measurement with Standard assembly f 2200 Ohm. ............................................13  
Layout recommendations ....................................................................................13  
PCB stack ......................................................................................................14  
Gerber Top...................................................................................................14  
Gerber Bottom ...................................................................................................15  
Assembly Top....................................................................................................16  
Bill of Material ................................................................................................17  
Version History.........................................................................................18  
3.4  
4
4.1  
4.2  
4.3  
4.4  
4.5  
4.6  
4.7  
4.8  
4.9  
4.10  
4.11  
4.12  
4.13  
5
1 Disclaimer  
Please note that the provded reference design board, evaluation board, verification board or  
demonstration board (hereafter named “demonstration circuit board”) are experimental  
printed circuit boards and are therefore intended for device demonstration and evaluation  
purposes only for semiconductor integrated circuits supplied by austriamicrosystems. The  
demonstration circuit boards are not production qualified. This application has not been  
certified accrding to CE/FCC/EMC requirements. Device parameters measured with these  
demonsration circuit boards may not represent typical production test data.  
THDEMONSTRATION CIRCUIT BOARDS ARE SUPPLIED WITHOUT WARRANTY  
OF ANY KIND, EXPRESSED, IMPLIED OR STATUTORY, INCLUDING BUT NOT  
LIMITED TO, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS  
FOR A PARTICULAR PURPOSE. AUSTRIAMICROSYSTEMS ACCEPTS NO  
LIABILITY WHATSOEVER ARISING AS A RESULT OF THE USE OF THESE  
DEMONSTRATION CIRCUIT BOARDS.  
Proprietary and Confidential  
2
The fee associated with the demonstration circuit boards is a nonrecurring engineering  
fee (NRE) to partially defray the hardware and software engineering costs associated with the  
development and provision of the demonstration circuit boards.  
The demonstration circuit boards may be operated for demonstration or evaluation purposes  
in non-residential areas only. austriamicrosystems’ understanding is that the customer’s  
products using the semiconductor integrated circuits shall be designed in compliance with all  
applicable requirements of the appropriate regulatory agency (e.g. FCC, ETSI, CE, JQA,  
etc.) and will, upon testing and release, be in compliance with these regulatory requirements.  
Operation of the customer’s products must not cause harmful interference and must accept any  
interference. This application shall not be offered for end-customer sale or lease until  
certification is obtained.  
2 Introduction  
This application note describes the AS3911 general purpoe Demo board and is usage. The  
general purpose board is made for a flexible use, hece the digital part can be separated from  
the analogue part. This enables fast software dvelopment since the analogue part can be used  
out of the box.  
The analog section has several jumpers to allow custom antenna and capacitive electrodes to  
be used.  
Proprietary and Confidential  
3
3 Hardware  
3.1  
Block diagram  
The board compromise of a Micro controller with USB support, a LDO to supply the micro  
controller and the HF reader IC AS3911.  
3V3  
5V  
LDO  
3V3  
USB  
Connector  
Micro  
Controller  
USB  
Differential  
SPI  
EMC Filter  
5V  
Matching  
NW  
Antenne Feedback  
coil loop  
Tuning Capacitor  
bank  
AS3911  
Blocking Cap for  
LDO’s of: VDD,  
AGD, VSPA, VSPRFP  
U2  
Uchip  
UA  
EMC Filter Network  
Matching network  
Schematic level  
Proprietary and Confidential  
4
3.2  
EMC and Power supply concept  
For rejection of EMC due the rectangular carrier field generation, ferrite beads are placed  
close to the supply with additional capacitors next to the connector.  
C1  
10u  
L3  
U1  
BUS_PWR  
VBUS  
D-  
VBUS  
U2  
+3.3V  
1
3
2
VIN  
VOUT  
2
3
4
5
D-  
C4  
Ferritbeat  
D-  
D+  
C5  
1u  
C6  
1u  
D3  
Zener  
D+  
10u  
D+  
D1  
24V  
AS1360-33  
D2  
24V  
D4  
24V  
C2  
dnp  
C3  
BUS_GND  
Shield  
dnp  
GND GND  
GND GND  
GND  
GND GND GND  
GND  
GND  
USB_MINI_B  
L1  
Ferritbeat  
L2  
Ferritbeat  
GND  
GND  
Since the specification of USB-supply voltage can have wt case 4.5 Volt, the supply  
Voltage of the device might vary. AS311 has an inteal rgulator that measure the voltage  
and adjust the internal regulator such that the voltage on he output driver (for antenna) is  
0.3Volt below the supply votage. This adjustmet assure that the digital noise on the supply  
of the antenna driver can be rcted and the Voltagfor the antenna driver can be maximized.  
Hence, for evaluation purpose, we have impd a jumper P5 which can be used to provide  
an external voltage supply to the reader IC.  
Proprietary and Confidential  
5
3.3  
Digital section ( micro controller)  
VBUS  
P1  
R20  
10k  
+3.3V  
C9  
Header 8H  
GND  
R18  
100n  
10k  
+3.3V +3.3V +3.3V  
U3  
PIC27FJ64GB002  
C7  
10n  
R1  
10k  
R4  
10k  
R7  
10k  
R19  
470  
C10  
10u  
26  
17  
16  
MCLR  
PGED1  
PGEC1  
VCAP  
1
2
DISVREG  
R2  
10k  
R5  
10k  
R100  
10k  
8
GND  
RP4/SOSCI  
RA4  
C11  
3
4
9
RP2  
RP3  
RP6  
RP5  
RP9  
RP7  
RP8  
GND  
GND  
GND  
GND  
7
18p  
RA3  
C12  
PIC24FJ64GB  
SCLK 28  
MOSI 27  
INTR 15  
MISO 13  
SEN 14  
6
MCCLK  
SCLK  
MOSI  
INTR  
MISO  
SEN  
RA2  
GND  
18p  
R13  
R14  
R15  
R16  
R17  
220  
220  
220  
220  
220  
220 R12  
220 R8  
8MHz  
Y1  
23  
22  
21  
11  
RP15  
RP14  
RP13  
RB5  
Plug  
T1  
R25 470  
R26 470  
R23 470  
R24 470  
220 R9  
220 R10  
220 R11  
+3.3V  
V_RF  
+3.3V VBUS V_RF  
D5  
D6  
D7  
D8  
C8  
+3.3V  
R21  
27R  
100n  
R22  
27R  
R3  
dnp 0R  
R6  
GND  
D+  
D-  
P2  
+3.3V  
GN
Header 8H  
The used micro controller is a PC24 FJGB002 with internal USB.  
Three pins (Pin 1,2 and 3 of the micro controller) bing used for selection of  
different Hardware versions of boards.  
Four diodes (D5-D8) display the various condtions of the board.  
The connector P2 can used as a alternatie connction to an external micro controller  
or to connect to a new developed anasytem of AS3911. The selection can be  
done by un mount the coupling resisto(R13-17).  
3.3.1 Programming header P1  
P1 is the programming header fhe microchip controller. The pin order on the header P1 is  
exactly the same as being used on the microchip tool chain, hence no special adapter is  
needed.  
Proprietary and Confidential  
6
3.4  
Analog section  
Following is the schematic of the analog section incl. AS3911 and its external components  
Proprietary and Confidential  
7
This setup is made to demonstrate almost all the capabilities of AS3911. The salient features  
are:  
Differential antenna  
Capacitive wakeup (possibility to attach external electrodes)  
Antenna tuning trimming capacitors  
27MHz Crystal  
supply noise rejection  
High sensitivity  
Low impedance driver stage  
3.4.1 Power concept  
AS3911 has internal LDO that needs to be decoupled with capacitors of 2.2 microF and 10  
nF. These pins are  
AGD (analogue ground)  
VSP_D (to supply the logic of AS3911)  
VSP_A (to supply the analogue part of AS3911)  
VSP_RF (to supply the driver stage of AS3911)  
AS3911 contains internal level shifter that enables to connect to micro controller with  
different VDD than AS3911. Pin 1 shall be connected to the same Voltage as the supply of  
the micro controller.  
GND as well as the supply line are being connected with a ferrite bead to reject the EMC  
disturbance caused by the HF driver.  
3.4.2 Antenna stage  
The Antenna stage consists of a two stage Filter network and a matching. The two stage filter  
shall reject higher harmonics of the 13,56 MHz carrier. Since inductors are non-ideal  
components and the self-resonant frequency of the second coil is around 400 MHz, we  
propose to use a two staged filter.  
The first stage has a corner frequency above 200 MHz and will reduce the harmonics at the  
higher frequencies.  
The second stage has a corner frequency below 10 MHz and will reject frequencies in the  
lower frequency band.  
The matching network follows the filter and adapts the power from the driver to the antenna.  
The tuning consists of external capacitors and chip internal switches. In case the switches are  
open, the antenna Voltage is directly applied to the input pin of the chip.  
Since the expected Voltage of the Antenna can be high, additional capacitors for voltage  
limitation can be applied. The AS3911 can accept voltages up to 30V on its antenna tuning  
pins.  
The input pins are being connected by a capacitive divider. The voltage on that pins shall be  
less than 3.3 Volt.  
Proprietary and Confidential  
8
3.4.3 Capacitive wakeup  
The capacitive wakeup consists of two pins that are each connected to an electrode and are  
protected against ESD with a gas discharge element.  
Since that pins can also be used as test outputs, an additional UFL connector is mounted.  
4 Measurement  
4.1  
Current consumption  
The measurement is being done across the AS3911 supply jumper P5.  
AS3911 working condition  
Current consumption in  
mA  
After startup  
7,58  
en=1, rx_en=0, tx_en=0  
en=1, rx_en=1, tx_en=0  
en=1, rx_en=1, tx_en=1  
en=0, rx_en=0, tx_en=0, wu=1  
14,97  
150  
0.002  
4.2  
Antenna stage  
Used equipment:  
Network Analyzer HP 8753C Network analyser  
Parameter test set 85047A Test set  
4.3  
Measurement of the antenna Parameters  
The parameters of the antenna are done in following sequence  
1: Start with the measurement of the serial Inductance and the serial resistor at a frequency  
that is far off the self-resonance of the antenna. The chosen frequency is 1 MHz  
@ 1 MHz we get:  
LPC = 940 nH  
RDC = 470 mOhm  
2. Measurement of the self-resonance (The point in which the impedance will be reel, all  
reactance’s will be zero.  
=> fres ~ 59 MHz  
RP,CAR = 5000 Ohm  
Using the inductance value that are being measured at 1 MHz, the resonance capacitor can be  
calculated with the formula  
1
1
C =  
=
= 7,74pF  
(2*Π * fres)2 * LPC (2*Π *59MHz)2 *940nH  
The value of the parallel resistor has to be converted from the self-resonance for the working  
frequency. The main reason for that conversion is the skin effect of the antenna, thus a  
correction factor can be given by:  
Proprietary and Confidential  
9
fres  
59  
K =  
=
= 2,085  
ftune  
13,56  
Which will end up in Rp2 at fc= K*RDC  
R
=
PC2  
K
10,4 kΩ  
≅  
Finally  
All components of the antenna are now known and a replacement for the antenna circuit can  
be drawn.  
The serial resistor of the coil can be converted with the approximation formula of the Q-  
factor  
ω
L
Rp  
(ω  
L)2  
Q =  
Rp =  
=14kOhm  
Rs  
ω
L
Rs  
The complete resistor will thus be a parallel schematic of the resistor due to DC component  
and the self-resonance component  
Rp1* Rp2  
Rpc =  
6,02kOhm  
Rp1+ Rp2  
All components of the antenna are known and a model of the antenna can be given:  
The values for the wanted resonance circuit are therefore:  
RPC =6,02 kOhm  
CPC= 7,74 pF  
LPC= 940 nH  
4.4  
Determination of the Antenna resistor  
The Antenna Q Factor can then be calculated as  
RPC  
RP  
6,02kOhm  
Q =  
=
=
= 75  
(
ω
L)  
(ωL) 2*Π *13,56MHz *940nH  
Proprietary and Confidential  
10  
Since the antenna works like a filter around it resonance frequency and the subcarrier is  
848kHz apart from the carrier, the bandwidth and thus the Q factor need to be adapted. The  
Bandwidth is defined based on the sub carrier frequency.  
fres  
848kHz  
Q =  
=
13  
fres 13,56MHz  
Since AS3911 can work due its excellent sensitivity in high Q environment, the Q factor can  
be increased to values above 13 and for that board Q is set to 20.  
And the parallel target resistor can then be calculate to  
RT = Q*(ωL)  
RT = 20*(2*13MHz*940nH) =1601Ohm  
Taking the parasitic resistor RPC from the antenna into account, the physical assembled  
resistor can be calculated to  
RPC RT  
6020*1601  
RP =  
=
= 2181Ω  
RPC RT 6020 1601  
The next available physical value is 2200 Ohm.  
4.5  
Matching of the driver  
The matching is done from the driver resistor towards the antenna resistor.  
The driver resistor can be assumed with 2 Ohm.  
Since the antenna is being used differential, only half of the antenna shall be considered for  
the matching.  
Matching resistor on antenna side: RP=1090 Ohm  
Antenna coil  
LP=470nH  
Driver  
resistor  
Matching  
resistor  
Antenne coil  
EMC Filter Network  
Matching network  
Using the program smith.exe from Bern University of applied science, following matching  
with physical available values is found.  
Proprietary and Confidential  
11  
2 Ohms are being matched to 1220 Ohm.  
According to the smith chart, the parallel capacitor shall be 89 pF. This capacitor is being  
composed out of the parasitic capacitance of the antenna, the parasitic capacitance of the  
tracks / voltage divider of the input and the tuning capacitor.  
Capacitor  
Value  
pF  
Note  
Parasitic antenna capacitor  
15,4  
Measured value of 7,7 pF  
needs to be multiplied by two  
due to the differential stage  
Capacitor divider (10 pF)  
plus 2 pF parasitic on each  
tuning inputs (4x2 pF)  
Parasitic of the capacitive Assumed to be18  
divider and tuning inputs  
Tuning capacitor  
Result  
56  
88  
Half of the maximum tuning  
capacitor bank  
4.6  
Verification of the Q factor in the time domain  
The resonance circuit envelope can be calculated with an exponential function  
Falling edge:  
Proprietary and Confidential  
12  
2*Πfc  
t  
t  
Q
U f = e τ = e  
Rising edge:  
2*Πfc  
t  
t  
Q
Ur = 1e τ = 1e  
Thus if the time constant (37% of the maximum amplitude) is known, the Q factor is  
calculated to:  
QB =  
τ
*2*Π * fc  
Measurement with Standard assembly of 2200 Ohm.  
4.7  
With TF=310 ns  
With TR=205 ns  
QR=26  
QF=17  
4.8  
Layout recommendations  
AS3911 is a high integrated device that allow easy layout. There are only a few layout rules to  
consider.  
Use a solid ground plan under the chip and use thermal via under the chip to dissipate the heat  
of and enable a low ohmic connection of the exposed pad to the ground plane.  
Take care that the decoupling capacitors of the LDO are close to the chip. Use thick wires for  
the decoupling tracks and place the 10nF capacitor closest to the chip.  
Use a symmetric layout for the antenna stage  
Do not cross the digital lines with the analogue lines.  
Take care on the signals VSN_RF, VSP_RF and the two output pins RFO1 and RFO2. These  
pins build up the internal driver stage. Tracks on those four pins shall be short and ground  
connections must be solid.  
Proprietary and Confidential  
13  
4.9  
PCB stack  
The PCB stack is made of a two layer PCB with 1.6 mm core material and 35micro (43 micro  
final ) copper.  
4.10  
Gerber Top  
Proprietary and Confidential  
14  
4.11  
Gerber Bottom  
Proprietary and Confidential  
15  
4.12  
Assembly Top  
Proprietary and Confidential  
16  
4.13  
Bill of Material  
Part Info  
Reference  
Footprint  
Producer  
Distributor  
Distributor Number  
count  
Integrated  
Circuits (IC)  
AS3911  
AS1  
U2  
QFN32  
austriamicrosystems  
austriamicrosystems  
Microchip  
1
AS1360  
SOT23  
1
PIC27FJ64GB002  
SMD resistor  
10k  
U3  
QFN28_6x6  
Digikey  
Digikey  
PIC24FJ64GA002T-  
I/MLTR-ND  
R1, R2, R4, R5, R0402  
R7, R18, R20,  
R100  
Yageo  
311-10KGRTR-ND  
8
0R  
R6,R29  
R0402  
Yageo  
Digikey  
Digikey  
311-00JRTND  
P220GTND  
2
220R  
R8, R9, R10, R11, R0402  
R12, R13, R14,  
R15, R16, R17  
Panasonic-ECG  
10  
470R  
R19, R23, R24, R0402  
R25, R26  
Stackpole  
Electronics  
Y
Digikey  
RMCF0402JT470RTR-ND  
5
27R  
R21, R22  
R0402  
R0402  
R0402  
Digikey  
Digike
Dgiy  
311-27JRTR-ND  
311-330JRTR-ND  
311-2.2KJRTR-ND  
2
1
1
330R  
R27  
Yag
Yage
2k2  
R28  
SMD capacitors  
10u  
C1,C4,C10  
C5,C6  
C0805  
03  
TDK Corporation  
Digikey  
445-1371-2-ND  
3
1u  
Taiyo Yuden  
Yageo  
Digikey  
Digikey  
587-2834-2-ND  
311-1042-2-ND  
2
6
10n  
C7, C15, C18, C040
C24, C29, C30  
100n  
18p  
C8, C9  
C0402  
AVX Cooration  
rporation  
Digikey  
Digikey  
478-1239-2-ND  
445-1238-2-ND  
2
4
C11, C12, C1C0402  
C16  
2u2  
C14, C17, C21, C0603  
C32, C33  
TDK Corporation  
Digikey  
587-2983-2-ND  
5
6p8  
12p  
100p  
27p  
C20, C34  
C23, C35  
C25  
C0402  
C02  
040
402  
TDK Corporation  
Yageo  
Digikey  
Digikey  
Digikey  
Digikey  
445-4887-2-ND  
311-1016-2-ND  
311-1024-2-ND  
311-1019-2-ND  
2
2
1
2
Yageo  
C27, C36  
Yageo  
56p  
C31, C37  
C38, C43  
C44, C47  
C0402  
C0402  
C0402  
Yageo  
Yageo  
Yageo  
Digikey  
Digikey  
Digikey  
311-1022-2-ND  
311-1021-2-ND  
311-1028-2-ND  
2
2
2
47p  
470p  
330p  
C5, C
C48C49  
C0  
C0402  
C0603  
C0603  
C0603  
C0603  
Yageo  
Digikey  
Digikey  
Digikey  
Digikey  
Digikey  
311-1027-2-ND  
445-1248-2-ND  
445-5039-2-ND  
445-1281-2-ND  
399-1049-2-ND  
2
2
1
2
2
120p  
TDK Corporation  
TDK Corporation  
TDK Corporation  
Kemet  
6p8  
100p  
C51, C54  
C52, C53  
10p  
SMuctors  
10n  
L4,L5  
L0603  
L0805  
L0805  
TDK Corporation  
Murata  
Digikey  
Digikey  
Digikey  
445-1492-2-ND  
490-5669-2-ND  
587-1911-2-ND  
2
2
5
20n  
L7,L8  
Ferritbead  
SMD diodes  
24V  
L1, L2, L3, L6, L9  
Taiyo Yuden  
D1, D2, D4  
D3  
D0603_SUP  
RESSOR  
SOD323F  
(SC-90)  
Farnell  
Digikey  
1470613  
3
1
Zener  
Comchip  
Technology  
641-1068-2-ND  
Proprietary and Confidential  
17  
SMD LED  
LED_LUMEX  
Oscillator  
27.12MHz  
D5,D6,D7,D8  
Q1  
Led_0402_L  
umex  
Kingbright Corp  
Digikey  
Digikey  
754-1104-2-ND  
490-5581-2-ND  
4
1
Crystal FA- Murata  
20H  
40.0000MF1  
5Z-AC3  
Mechanical  
components  
USB_MINI_B  
U1  
SOCKET_S  
MD_USB_M  
INI  
Hirose Electric  
Digikey  
Digikey  
H2959TR-ND  
1
Not Used  
10u  
C2,C3  
Y1  
C0603  
TDK Corporation  
445-4112-2-ND  
2
1
8MHz  
Crystal FA-  
20H  
40.0000MF1  
5Z-AC3  
Header 8H  
P1, P2  
P3, P4  
HDR1X8  
2
2
U
FL Socket  
-
Surface Mount  
Header 2  
P5  
HDR1X2  
HDR1X2  
HDR1X3  
TESTPOINT  
PIN1  
1
2
1
1
4
8
MHDR1X2  
Header 3  
Plug  
P6, P7  
P8  
T1  
Plug  
T2, T3, T4, T5  
dnp  
C19, C22, C26, C0402  
C28, C39, C40,  
C41, C42  
dnp  
R3  
02  
1
2
CSA20-141N DNP  
U4, U5  
6-080_M  
Tolerance if not other specified  
Capacitor NP0/COG  
Capacitor X7R:  
Capacitor Y5V:  
Tantalum  
2%  
10%  
+80% 20%  
20%  
Resistor  
5%  
Inductivity  
5%  
5
Version History  
Version  
100  
Originator  
tlu  
Change log  
Initial Version  
Proprietary and Confidential  
18  
For further information please contact  
The Wireless Business Line  
Schloss Premstaetten  
A-8141 Unterpremstaetten  
AUSTRIA  
Tel: +43-(0)3136-500-5473  
FAX: +43-(0)3136-500-4141  
Subject to change without notice  
Proprietary and Confidential  
19  

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