RF Amplifier for NXP Contactless Reader IC’s, MFRC500, MFRC530, MFRC531, CLRC632, SLRC400

Design of Overall System
Schematic
All above mentioned components will be connected to following schematic.

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Fig 9. Schematic of RF Amplifier and Receiver Stage

Layout
Hints for the design:
–The supply voltage should be EMC refined with suitable capacitors.
–Spatial separation of the amplifier system and antenna is possible.
–Keep tracks short.
–Flood the prints with GND layers to avoid loops.
–Do not connect the virtual GND of the antenna to the GND of the supply voltage to avoid common-mode currents.
The following plot Fig 10 shows top layer and bottom layer of a sample print board of the amplification system.

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Fig 10. Top (red) and Bottom (blue) layer for the RF Amplifier System

Results
The following diagrams in Fig 11 shows how the RF amplifier circuitry can improve proximity reader characteristics. The magnetic field strength shown in Fig 11 has been increased by the amplification
system compared to the original system described in [6]. The reading distance for 1.5A/m, measured under maximum card loading conditions [8], was increased by 50%.
NOTE: In this case the Q-factor of the antenna in the original system is approximately twice as high as for the sample antenna used in cooperation with the amplification system.

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Fig 11. H-Field versus Reading Distance in mm to the Antenna Surface
Another important feature of the amplification system is that signal shapes according to ISO/IEC 14443-2 (2000) [7] can be easily achieved as shown in Fig 12.

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Fig 12. Pulse shape for 106 kbit/s (left) and 848 kbit/s (right) both Type-A

The amplification system offers linearity allowing proper ISO/IEC 14443-2 (2000) [7] Type-B data transmission with standard settings of the reader chip.

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Fig 13. Type-B Communication

The sideband level sensitivity must not exceed the limit given in the standard ISO/IEC CD 14443-2 (2007) [9] for a given value of the field strength. The next plot Fig 14 proofs that the requirement can be easily met.

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Fig 14. Measured Sensitivity versus H-Field

NOTE: The higher the H-field in the transmitting path, the higher the sensitivity of the receiving path in order to achieve data transmission and reception in desired quality.

SL RC400 I Code Reader IC
MIFARE MF RC500; Highly Integrated ISO 14443A Reader IC
MIFARE MF RC 530 ISO14443A reader IC
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MIFARE and ICODE CL RC632 Multiple protocol contact less reader IC
Directly Matched Antenna Design, Application Note
ISO/IEC 14443-2 (2000)
ISO10373-6 Identification cards — Test methods part 6: Proximity cards
ISO/IEC CD 14443-2 (2007)