INTEGRATED CIRCUITS
Design of MF RC500 Matching
Circuits and Antennas
May 2000
Objective
Revision 1.0
SECURED, STRICTLY CONFIDENTIAL
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Semiconductors
Philips Semiconductors Objective Rev. 1.0 May 2000
Application Note Design of MF RC500 Matching Circuits and Antennas
HKu 2 SECURED, STRICTLY CONFIDENTIAL
CONTENTS
1 INTRODUCTION .........................................................................................................................4
2 SYSTEM FUNDAMENTALS.........................................................................................................5
2.1 Block Diagram.............................................................................................................................5
2.2 System Configurations .................................................................................................................6
2.3 The MIFARE
®
RF Interface..........................................................................................................7
2.3.1 Energy Transmission ...................................................................................................................8
2.3.2 Data Transmission RWD à Card..................................................................................................8
2.3.3 Data Transmission Card à RWD................................................................................................10
3 DESIGN OF MF RC500 MATCHING CIRCUITS AND ANTENNAS...............................................12
3.1 Basic Design Rules....................................................................................................................12
3.2 Estimation of the Optimum Antenna Size ....................................................................................14
3.3 Directly Matched Antennas.........................................................................................................17
3.3.1 EMC Circuit...............................................................................................................................17
3.3.2 Receiving Circuit........................................................................................................................17
3.3.3 Antenna Matching Circuit for Directly Matched Antennas..............................................................19
3.4 50 Ω Matched Antennas.............................................................................................................23
3.4.1 EMC Circuit...............................................................................................................................23
3.4.2 Receiving Circuit........................................................................................................................23
3.4.3 50 Ω Full Range Solution ...........................................................................................................24
3.4.4 50 Ω Short Range Solution.........................................................................................................26
3.4.5 Antenna Matching Circuit for 50 Ω Antennas ...............................................................................27
4 ENVIRONMENTAL INFLUENCES..............................................................................................30
4.1 Metallic Antenna Environment ....................................................................................................30
4.2 Multiple Antennas ......................................................................................................................30
4.3 Temperature..............................................................................................................................30
5 ANTENNA SHIELDING, COMPENSATION................................................................................31
5.1.1 Electrical Shielding ....................................................................................................................31
5.1.2 Compensation ...........................................................................................................................32
5.1.3 Ferrite Shielding ........................................................................................................................33
6 EXAMPLE DESIGN OF MF RC 500 ANTENNAS ........................................................................36
6.1 General Layout Hints .................................................................................................................36
6.1.1 EMC Filter and Receiving Circuit ................................................................................................36
6.2 Layout of the Antenna and the Matching Circuit ...........................................................................36
Philips Semiconductors Objective Rev. 1.0 May 2000
Application Note Design of MF RC500 Matching Circuits and Antennas
HKu 3 SECURED, STRICTLY CONFIDENTIAL
6.3 Example for a Directly Matched Antenna.....................................................................................37
6.3.1 Shielded and Compensated Rectangular Antenna.......................................................................37
6.3.2 Rectangular Antenna .................................................................................................................38
6.3.3 Shielded Rectangular Antenna ...................................................................................................39
6.4 Example for an 50 Ω Matched Antenna .......................................................................................40
6.4.1 Compensated Rectangular Antenna............................................................................................40
6.4.2 Compensated Circular Antenna ..................................................................................................41
6.4.3 Shielded Circular Antenna..........................................................................................................42
7 ANTENNA TUNING...................................................................................................................44
7.1 Tuning Methods for an Optimum Operating Distance ...................................................................45
7.1.1 Tuning of Directly Matched Antennas ..........................................................................................45
7.1.2 Tuning of 50 Ω Matched Antennas ..............................................................................................46
7.2 Checking the Q-Factor ...............................................................................................................53
8 REFERENCES..........................................................................................................................55
9 ANNEX A..................................................................................................................................56
9.1 Abbreviations ............................................................................................................................56
9.2 Calculation of the Antenna’s Coil Inductance...............................................................................56
9.3 Estimation of the Coils’ Resistance .............................................................................................57
10 DEFINITIONS ...........................................................................................................................58
11 LIFE SUPPORT APPLICATIONS ...............................................................................................58
12 REVISION HISTORY .................................................................................................................59
MIFARE
is a registered trademark of Philips Electronics N.V.
Philips Semiconductors Objective Rev. 1.0 May 2000
Application Note Design of MF RC500 Matching Circuits and Antennas
HKu 4 SECURED, STRICTLY CONFIDENTIAL
1 INTRODUCTION
This application note is intended to support RF-related design–in of the MF RC500 MIFARE
®
reader IC. The
aim is to provide the required understanding of the MIFARE
®
RF interface (ISO 14443A) to design
application specific antennas and matching circuits to achieve the best performance for a communication
with a contactless MIFARE
®
card. This paper shall give a background on the system’s RF part and an
overview on the procedure how to design and tune antennas for standard applications. Two different
antenna and matching concepts are explained in detail as well as examples for the antenna design itself.
Furthermore, the complete tuning procedure is described. As part of the Annex, the interested reader will find
a detailed theoretical description of the RF interface.
Philips Semiconductors Objective Rev. 1.0 May 2000
Application Note Design of MF RC500 Matching Circuits and Antennas
HKu 5 SECURED, STRICTLY CONFIDENTIAL
2 SYSTEM FUNDAMENTALS
2.1 Block Diagram
The MF RC500 is member of a new family of highly integrated reader ICs for contactless communication
based on 13.56 MHz. The MF RC500 supports all layers of ISO 14443. Figure 2-1 shows a simplified block
diagram.
Analog Circuitry
Integrated
Demodulator,
Bit-Decoder,
Output Drivers
Crypto 1 Security
& Key Memory
Status & Control
Data Processing
Parallel
µController
Interface
MF RC500
Figure 2-1. Simplified MF RC500 Block Diagram
The MF RC500 fulfils the following functions:
§ The parallel µ-Controller interface detects automatically the connected 8 bit parallel interface.
§ The data processing part performs the parallel to serial conversion of the data. It supports the framing
generation check, the CRC/Parity generation and check as well as the bit coding and processing. All
layers of ISO14443-A are supported, as the MF RC500 operates in full transparent mode.
§ The status and control part allows the configuration of the device to environmental influences to achieve
the best performance for each application.
§ The Crypto1 stream cipher unit is implemented to support communication to MIFARE
®
CLASSIC
products.
§ A secure non-volatile key memory is included to store Crypto 1 key-sets.
§ The analog part includes two internal bridge driver outputs to achieve an operating distance up to
100mm depending on the antenna coil and the environmental influences. Furthermore, the internal
receiving part allows the receiving and decoding of data without external filtering.
