ST ST25RU3993 Manuale utente

August 2020 UM2742 Rev 1 1/44

UM2742

User manual

High-power RFID reader system based on ST25RU3993

Introduction

The ST25RU3993-HPEV is a high-power RAIN®(UHF) RFID reader system based on the

integrated reader IC ST25RU3993.

The purpose of ST25RU3993-HPEV is to provide a comprehensive RAIN RFID reader

system that allows the user to evaluate the properties and the features of ST25RU3993. To

achieve this goal the ST25RU3993-HPEV board, differently from a typical reference design

approach, combines a high RF power and a low RF power RFID reader on a single PCB.

Additionally, the ST25RU3993-HPEV board has been outfitted with numerous easy to

access test points and measurement possibilities. With minor modification effort it is

possible to change the architecture of the reader. For example, it is possible to control the

RF circuitry with external MCU or vice versa. Bypassing the external on-board power

amplifier or alternate antenna configurations are additional possibilities.

The ST25RU3993-HPEV is controlled by a graphical user interface (GUI) running on a host

PC. The corresponding interface is a USB/UART bridge (requires driver installation). The

GUI can be found on dedicated pages on www.st.com.

The board supports tuning the radio frequency from 840 to 960 MHz. and provides two SMB

(male) antenna connectors that can be controlled via the GUI. To enable scanning for RAIN

RFID transponders connect a suitable 50 ΩUHF antenna for the targeted frequency range.

Figure 1. ST25RU3993-HPEV board

www.st.com

Contents UM2742

2/44 UM2742 Rev 1

Contents

1 Standard connection setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1 Board features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1 RF circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 Microcontroller and connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.3 Firmware programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.4 Boot mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.5 Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.6 Test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2.6.1 Analog test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.6.2 Digital test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.6.3 Probing RF signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3 Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4 PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

UM2742 Rev 1 3/44

UM2742 List of tables

List of tables

Table 1. TXCO / Crystal configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Table 2. MCU interfaces and buttons (see Figure 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 3. MCU - SPI interface and ST25RU3993 connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 4. SPI interface pinout at J10, J12 and J13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 5. UART connections and pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 6. MCU connections to buttons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 7. MCU connections to LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 8. MCU connections to RF switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 9. Connections to JLINK (SWD) interface and pinout of connector . . . . . . . . . . . . . . . . . . . . 17

Table 10. Typical voltage levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 11. Connection of components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 12. Connections of analog test points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Table 13. Supply voltages of analog test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Table 14. RF test points – Default power levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Table 15. List of schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 16. PCB stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Table 17. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Table 18. DC characteristics (VBUS = 5.0 V, 25 °C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Table 19. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

List of figures UM2742

4/44 UM2742 Rev 1

List of figures

Figure 1. ST25RU3993-HPEV board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Standard connection setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3. ST25RU3993-HPEV functional diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 4. Power detector voltage characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 5. Main digital interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 6. JLink connection using the needle adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 7. Entering the Boot mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 8. Test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 9. Connection of a voltmeter / ammeter to the supply voltage test points . . . . . . . . . . . . . . . 23

Figure 10. RF test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 11. Connecting to the RF test points with the SMA adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 12. System overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 13. UHF RFID reader IC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 14. External power amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 15. Carrier cancellation circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 16. Antenna switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 17. RF shield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 18. USB supply / UART bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 19. Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 20. Supply LDOs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 21. External interfaces and connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 22. Top layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Figure 23. RF GND layer (L2), GND layer (L4) and bottom layer (L6) layout . . . . . . . . . . . . . . . . . . . 39

Figure 24. Power layer (L3) layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 25. Routing layer (L5) layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

UM2742 Rev 1 5/44

UM2742 Standard connection setup

1 Standard connection setup

The typical reader setup is shown in Figure 2.

Figure 2. Standard connection setup

The host PC running the GUI is connected via a Micro-USB cable. The external power

amplifier on the ST25RU3993-HPEV board is powered through the 6 V power adapter and

must be connected when the external PA TX option is used. The antenna is connected to

the active antenna port through a coaxial cable. A transponder is within the antenna range.

1.1 Board features

ST25RU3993 RAIN (UHF) RFID reader IC

ISO/IEC 18000-63:2015 / Gen2V2

GB/T 29768-2013

Two SW-controlled power amplifier (PA) options:

– External PA: 31 dBm max. TX power

– Internal PA: 18 dBm max. TX power

Configurable TX power level

Power detector to monitor TX power

Automatic carrier cancellation for improved RX sensitivity

Differential RX input

Maximum sensitivity: -80 dBm

Adaptive / manual RX gain adjustment

Tunable radio frequency: 840 to 960 MHz

Minimum frequency step: 25 kHz

External frequency reference (20 MHz) assembly option

Adaptive / manual anti-collision slot options

Continuous wave or Modulated RF output test modes

Two antenna ports: SMB (M)

Automatic / Manual antenna port switching

Carrier sense TX option (LBT)

Standard connection setup UM2742

6/44 UM2742 Rev 1

UHF tag RSSI measurement

Configurable SELECT command mask

UHF transponder EPC Read / Write

Transponder read based applications trigger

Custom reader TX command editor tool

Customizable Gen2 TX commands

Direct TX modulation through MCU for proprietary protocol support

Store / Recall reader configuration

Register map

Buzzer

Host interface and supply

– USB/UART bridge

– USB receptacle: Micro, B-Type

– Main supply: 6 V DC jack

MCU:

– STM32L476RGT6 (Arm®(a) 32-bit Cortex®-M4)

– 64 MHz

– 128-Kbyte RAM

– 1-Mbyte Flash memory

– SPI Mode 1 (5 MHz)

– Firmware programmable through USB/UART

– SWD debug interface

–LEDindicators

– Power amplifier selection

– Carrier cancellation tuning activity

– Carrier cancellation tuning OK

– OSC OK (20 MHz external reference)

–PLLOK

–RFON

– No tag response

– Tag CRC error

–Tagfound

Test points:

– In-circuit RF power levels and signals

– RFID communication TX and RX

– UART and SPI signal lines

– UART_LOG for debugging purposes

a. Arm is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.

UM2742 Rev 1 7/44

UM2742 Standard connection setup

– Control voltage of internal VCO

– RF power detector output voltage

– 20 MHz reference signal

– External PA BIAS voltage

– LDO output voltages

– LDO outputs: jumpers for current consumption measurement

– Main supply: jumper for current consumption measurement

– Antenna switch state

– Power amplifier selection switch state

Buttons:

– MCU reset

– MCU boot mode

Standard connection setup UM2742

8/44 UM2742 Rev 1

Figure 3. ST25RU3993-HPEV functional diagram

IRQ

RF switch:

SKY13431

374LF

Carrier

ancellation

circuit

SPI (Mode 1)

D-

D+

USB c

onnector:

MICRO-B

3.3V

3.6V

LDO:

LD39100PUR

PA_LDO_EN

PA_SW_V1

PA_SW_V2

ANT_SW_V2

ANT_SW_V1

CPL-10dB

CPL-20dB

RFOPX

RFONX

PAOUT_P

PAOUT_N

93_RF_OUT

93_intPA

PA_OUT

LP_Filter_IN

LP_Filter_OUT

TX_RX

Power detector:

MAX4003EUA

ANT1

ANT2

ETC_x

MOSI

CLK

RF_Detector

SWD connector:

(

TC2050-IDC-

FP)

SWD

Buzzer:

PKMCS0909E4000

OSCO

3.3V

LDO:

LD39100PUR

LED:

MCU

LED:

RF ON

LED:

Tuning

LED:

Tuned

LED:

OSC OK

LED:

ANT1

LED:

ANT2

LED:

Tag R

esp

LED:

Tag

CRC E

rr.

LED:

Tag

LED:

Int_PA

LED:

Ext_PA

LED:

PLL OK

SPI

+ IRQ + EN

Carrier

cancellation

UART

UART_LOG_TX

PA_LDO_EN

OSCO

VCO

EXT_PA_BIAS

RF detector

Button:

RESET

Button:

BOOT

Legend

Component

Test point /

onnector

LED Button

Logic

Supply

DC power j

ack

OD: 6.4 mm

ID: 2.1 mm

OSCI

Antenna selection

switch state

PA selection

switch state

LED:

BOOT (red)

VBUS 5V

USB/UART

bridge:

FT231XQ-R

Balun:

BD0810J50100AHF

20 dB coupler:

DC1722J5020A

Low pass filter:

0900LP15B0063

10 dB coupler:

DC1722J5020A

TCXO:

TXEAADSANF-

Crystal:

(optional)

NX3225SA-20

Antenna

port 2

SMB Male

Antenna

port 1

SMB Male

VBUS 5V

Analog

RF switch:

SKY13431

374LF

PA LDO:

LD39100PUR

MIX_INP

MIX_INN

MCU:

STM32L476RG

Power

mplifier:

TQP9107

Balun:

BD0810J50100AHF

Balun:

0900BL15C050

UHF RFID reader IC:

ST25RU3993

UM2742 Rev 1 9/44

UM2742 Hardware description

2 Hardware description

2.1 RF circuit

The main component of the RF circuit is the ST25RU3993 device, which receives digital

baseband transmit data and commands from the MCU via the SPI interface. It then frames

these data and automatically encodes them into PIE symbols. Based on the PIE encoded

symbols ST25RU3993 creates a sinusoidal shaped modulation signal (either ASK or 

PR-ASK), which modulates the RF carrier. ST25RU3993 synthesizes its RF carrier

frequency with a VCO / integer-n phase locked loop (PLL). The frequency reference for the

PLL can be either a 20 MHz crystal oscillator or a temperature compensated crystal

oscillator (TCXO).

As shown in Table 1 the ST25RU3993-HPEV board accommodates both options, the

default configuration is the TCXO with a clipped sine wave output wave having 0.8 Vpp

amplitude. With a small modification it is possible to connect the existing crystal.

The output of the internal PLL- charge pump is connected to LF_CEXT (pin 45), and the

external part of the loop filter is placed in close proximity to it. An additional low-pass filter

stage is integrated in ST25RU3993 and is part of the loop filter circuit. The loop filter output

is the control voltage of the internal VCO.

Table 1. TXCO / Crystal configuration

Default Alternate (modified by user)

TCXO connected to ST25RU3993 Crystal connected to ST25RU3993

R54 and R55 not populated C51 removed, R54 and R55 populated

Hardware description UM2742

10/44 UM2742 Rev 1

The ST25RU3993 has two differential output port pairs. The low power output and the

internal power amplifier output. Depending on which differential output port pair is activated

the modulated carrier frequency will be amplified and output accordingly.

The low power output is intended for external signal amplification for a long read range

configuration of the ST25RU3993-HPEV reader. The low power output with its differential

output pin pairs RFONX (23) and RFOPX (24) is connected to a 2:1 balun, where the

transmit signal is transformed from a 100 differential to 50 Ωsingle-ended signal. The output

stage of the low power output is supplied by the VDD_B voltage generated and regulated by

ST25RU3993 itself. L3 and L4 act as a RF choke, C57 and C58 as bypass capacitors and

C65 and C54 as DC blocking capacitors. The signal then proceeds to the external power

amplifier to generate a high-power output signal with approximately 31 dBm in

ST25RU3993-HPEV default transmit power configuration.

The internal power amplifier is used for the short read range configuration of the reader. The

output pins of the internal power amplifier are PAOUT_N (16, 17) and PAOUT_P (20, 21). A

matching network and a 1:1 balun transforms the output of the internal power amplifier to a

50 Ωsingle-ended signal. The internal power amplifier is supplied by the on-chip generated

and regulated voltage VDD_PA. L1, L2 are acting as RF chokes, C12 and C14 are bypass

capacitors. After the balun the output power of the internal power amplifier is nominally

20 dBm.

Both RF output options the external power amplifier and the output of the internal power

amplifier are connected to an RF-switch which is controlled by the PC software (GUI) of the

ST25RU3993-HPEV reader. Only one RF output option can be active at a time. Note a UHF

RFID reader reference would typically offer only one RF output and hence the PA RF-switch

would be stripped from the design avoiding it’s introduced insertion loss of ~0.5 dB. So

would be the DC blocking capacitors which this RF-switch requires on all its RF terminals.

The output of the RF-switch is connected to a low-pass filter which attenuates the second

and third harmonic of the carrier frequency. The filtered transmit signal is then connected to

a 20 dB directional coupler, which takes a negligible small portion of the transmit power,

which is further attenuated by a pi-pad attenuator. The limited TX power sample is then fed

to the input a logarithmic power detector that converts the RF power to a corresponding DC

voltage. The output DC voltage of the power detector versus the generated RF power is

shown in Figure 4.

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