AN3394 Datasheet, PDF (1/29 Pages) STMicroelectronics – Antenna design and impedance matching guidelines for CR95HF multiprotocol contactless transceiver IC

AN3394
Application note
Antenna design and impedance matching guidelines
for CR95HF multiprotocol contactless transceiver IC
Introduction
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
October 2011
Doc ID 018754 Rev 5
1/29
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