AMS Radon AS3993 Installation and operating instructions

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Revision 1.0 / 2012/06/26
Application Note: UHF RFID Femto Reader
HW
-Description
AS3993
UHF RFID Single Chip Reader EPC
Class1 Gen2 Compatible

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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Table of Contents
1. Introduction..........................................................................................................................2
2. Key Features .......................................................................................................................3
3. Applications .........................................................................................................................4
4. Reader System Overview.....................................................................................................5
5Interfaces.............................................................................................................................7
5Reader System Description................................................................................................11
Copyright ..................................................................................................................................17
Disclaimer.................................................................................................................................17
Figure 1 - Reader Top......................................................................................................................... 5
Figure 2 – Reader Bottom................................................................................................................... 6
Figure 3 - USB Interface...................................................................................................................... 7
Figure 4 - UART Interface Connections.............................................................................................. 8
Figure 5 - MCU Debug Interface......................................................................................................... 9
Figure 6 - SPI Interface Connections................................................................................................ 10
Figure 18 - OAD Pads....................................................................................................................... 10
Figure 7 - RF Tracks - Impedance Calculation (dimensions in mil).................................................. 11
Figure 8 - RF Part - PCB Stackup.....................................................................................................11
Figure 9 - Reader System Components............................................................................................ 13
Figure 10 - Schematic Reader Section ............................................................................................. 14
Figure 11 - Schematic RF Section ....................................................................................................14
Figure 12 – Schematic Tuning Circuit............................................................................................... 15
Figure 13 - Schematic Controller Section.......................................................................................... 15
Figure 14 - Schematic Connector Section......................................................................................... 16
Figure 15 - Schematic Power Supply Section................................................................................... 16
5.1 USB..........................................................................................................................
7
5.2 UART Interface.........................................................................................................
8
5.3 MCU Debug Interface...............................................................................................
9
5.4 SPI Interface ..........................................................................................................10
5.1 RF Tracks – Impedance Calculation.......................................................................
11
5.2 Reader Part – PCB Stackup...................................................................................
11
5.3 RF Path..................................................................................................................
12
5.4 Power Supply.........................................................................................................
12
5.5 Schematics.............................................................................................................13

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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1. Introduction
The Femto Reader is a small form factor and low costs EPC Class 1 Gen 2 UHF RFID
demonstration reader system. Leveraging ams’ UHF RFID AS3993, provides close to the
industry’s lowest BOM cost, best in class power consumption with the least amount of
complexity.
Second only to ams Femto design the low reader BOM enables UHF RFID markets that have
previously been out of reach due to cost restraints. With regards to overall cost vs. performance
the FERMI UHF RFID demo reader is unmatched in the industry.
By using the internal PA delivering up to 20 dBm, it is ideally suited for cost and form factor
constraint applications.
The Femto demo reader features an antenna tuning circuit to re-tune the resonance frequency of
the antenna in case a de-tuning occurs. In addition the Femto reader features an antenna switch
to allow UHF RFID operation through an external antenna or the onboard chip antenna1.
The Femto reader is designed as such that it can be easily connected to an external host MCU
via SPI leaving the onboard MCU idle. The high level of integration found on the AS3993 UHF
RFID AS3993 allows for minimal code loading and quick implementation.
The designs come with free, fully portable code and all Gerber data and schematics. This allows
for a quick, trouble free design in.
1Not populated for Femto Version 1.x

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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2. Key Features
•Interface
oBetween the Controller and Host Computer: USB (optional UART)
oSPI between an off-board controller and the AS3993 via a low cost pin header
connection
oSMA (Female) connector for external antenna
•Special
oAntenna tuning circuit
oAntenna switch
oEnabled for onboard antenna
•5V power supply from USB.
•GUI
oAdjust Output Power
oAdjust Receive – Sensitivity
oAdapt to different frequency schemes (FCC ETSI)
oChange Gen2 specific parameters like BLF, Coding, Anti-Collision Slots, …
oDiagnostic Features: RSSI Measurement, Reflected Power Measurement
oSupport for sending AS3993 related direct commands
oAdvanced Tag Manipulations: R/W to different memory banks, define passwords
oAssociate tags with other applications like media player
oView and easily manipulate register settings with advance tool tip text.
oAntenna selection
oTuning circuit control
•Fully Gen 2 compliant, ISO 18000-6b & 6c
•Differential TX chip-output configuration
•Differential RX chip-input configuration
•Internal power amplifier with a maximum output power of 20 dBm

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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•Low cost MCU: Microchip (PIC24FJ64GB004)
•Indicator LEDs
3. Applications
Typical applications for the FERMI demo reader include:
• Embedded Consumer Applications
• Mobile Applications (Low Power Handheld, PDA’s, Smart Phones)
• Embedded Industrial Applications
• Gaming
• Desk top readers
• Low/Mid powered modules

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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4. Reader System Overview
Figure 1 - Reader Top
1. AS3993 UHF RFID AS3993 (ams)
2. Balun 2:1 (Johanson Technology)
3. Low pass filter
4. Directional coupler / combination (Johanson Technology)
5. Antenna tuning circuit
6. Loop Filter
7. OAD pins for debugging purposes
8. Antenna Switch
9. Onboard antenna (not populated)
10. Internal PA matching Circuit
11. UART interface
12. Debug interface

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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13. SPI pin header for external MCU
14. Indicator LEDs
15. SMA (female) connector for external antenna
Figure 2 – Reader Bottom
1. MCU C8051F340 (Silabs)
2. USB connector
3. TCXO
4. LDO (5 V → 3.5 V)

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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5 Interfaces
5.1 USB
Figure 3 - USB Interface
The USB is used to communicate to the host computer and to supply the reader system. The 5V
USB voltage is regulated down to 3.5 V.

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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5.2 UART Interface
In order to establish a connection to the host computer via UART it is recommend using an USB
TTL serial cable with 3.3 Volt (FTDI TTL-232R-3V3-WE). The UART connection is established
through P2. The 5 Volt power supply should be provided via the USB connector or J2.
Figure 4 - UART Interface Connections
Note: Once the firmware is programmed to communicate via UART the USB connecting is required
to reprogram the FW.

AS3993 – AN13 – Received Signal Strength Indicator (RSSI)
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5.3 MCU Debug Interface
To load the bootloader to the reader the debug interface connected to P4 should be used.
Figure 5 - MCU Debug Interface