ST公司的CR95HF是具有SPI和UART串行接入的多协议无接触13.6MHz收发器IC,可作为13.56MHz空中接口的模拟前端(AFE),支持ISO/IEC 14443 A和B, ISO/IEC 15693 (单或双用户)以及ISO/IEC 18092等协议,能管理阅读器模式的帧编码和译码,主要用在NFC, 接近标准应用.本文介绍了CR95HF主要特性,方框图和MCU的典型应用以及DEMO-CR95HF-A 演示板等效电路,天线电路框图,和DEMO-CR95HF-A电路与所用材料.

The CR95HF is an integrated transceiver IC for contactless applications.

The CR95HF manages the frame coding and decoding in Reader mode for standard applications such as NFC, proximity and vicinity standards.

The CR95HF embeds the Analog Front End for 13.56 MHz Air Interface.

The CR95HF supports ISO/IEC 14443 A and B, ISO/IEC 15693 (single or double subcarrier) and ISO/IEC 18092 protocols.

CR95HF主要特性:

■ Operating modes supported:

– Reader/Writer

■ Hardware features

– Dedicated internal frame controller

– Highly integrated Analog Front End (AFE)

for RF communications

– Transmission and reception modes

– Optimized power management

– Tag Detection modes

■ RF communication @13.56 MHz

– ISO/IEC 14443 A and B

ISO/IEC 15693

– ISO/IEC 18092

■ Communication interfaces with a Host Controller

– Serial peripheral interface (SPI) Slave interface

– Universal asynchronous

receiver/transmitter (UART)

■ 32-pin VFQFPN (5 x 5 mm) ECOPACK® package

CR95HF应用:

Typical protocols supported:

■ ISO/IEC 14443-3 Type A and B cards and tags

■ ISO/IEC 15693 and ISO/IEC 18000-3M1 tags

■ NFC forum tag: Types 2, 3 and 4

■ ST Dual Interface EEPROM

图1.CR95HF方框图

图2.CR95HF应用示意图

The goal of this application note is to provide guidelines to design a CR95HF antenna which impedance matches to the CR95HF impedance. This allows to achieve the best RF communications between the CR95HF transceiver integrated circuit (IC) and ISO15693 or ISO14443 RF memory tags.

The DEMO-CR95HF-A is a demonstration board for the CR95HF 13.56 MHz contactless transceiver. It is designed as a ready-to-use circuit board to interface with the CR95HF PC host demonstration software through an USB bus. The DEMO-CR95HF-A is powered by the USB bus and no external power supply is required. It is based on the CR95HF contactless transceiver with a 47x34 mm 13.56 MHz inductive etched antenna and its associated tuning components, and on a STM32F103CB 32-bit microcontroller that communicates with the CR95HF via the USB bus.

This document is structured as follows:

■ Description of the DEMO-CR95HF-A board

– Definition of CR95HF output impedance

Use of inductive antenna

– Impedance matching

■ Description of equivalent circuit

– CR95HF RF circuit modeling and description of antenna impedance matching circuit

– Calculation of the matching circuit optimized for ISO15693 memory tags

■ Read range estimate based on magnetic field calculation method for a rectangular Antenna Main criteria for key antenna design


图3.DEMO-CR95HF-A 演示板等效电路

图4.天线电路框图

其中：

R1,R5:

330 Ω. These resistors are used to limit the signal level on RX1-RX2. They must be considered in the calculation of the impedance matching circuit.

Cinput:

22 pF. Cinput is the integrated capacitor between RX1-RX2. As R1,R5, it must be considered for the impedance matching circuit

图5.CR95HF等效电路和匹配电路

图6.DEMO-CR95HF-A电路
DEMO-CR95HF-A 演示板元件列表：

详情请见：
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/DM00025644.pdf
和
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/APPLICATION_NOTE/DM00027198.pdf