ST ST25RU3993 User manual

August 2020 UM2742 Rev 1 1/44
1
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
3
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
43
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
43
– 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
EN
RF switch:
SKY13431
-
374LF
Carrier
c
ancellation
circuit
SPI (Mode 1)
5V
RX
TX
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
TX
Power detector:
MAX4003EUA
ANT1
ANT2
ETC_x
MOSI
CLK
RF_Detector
SWD connector:
(
TC2050-IDC-
FP)
SWD
Buzzer:
PKMCS0909E4000
OSCO
3.3V
3.3V
3.3V
3.3V
3.3V
LDO:
LD39100PUR
LED:
MCU
LED:
RF ON
LED:
Tuning
LED:
Tuned
LED:
OSC OK
LED:
ANT1
LED:
ANT2
LED:
NO
Tag R
esp
LED:
Tag
CRC E
rr.
LED:
Tag
LED:
Int_PA
LED:
Ext_PA
LED:
PLL OK
SPI
+ IRQ + EN
Carrier
cancellation
CS
UART
UART_LOG_TX
PA_LDO_EN
OSCO
VCO
EXT_PA_BIAS
RF detector
Button:
RESET
Button:
BOOT
Legend
Component
Test point /
c
onnector
LED Button
Logic
Supply
DC power j
ack
OD: 6.4 mm
ID: 2.1 mm
6V
OSCI
Antenna selection
switch state
PA selection
switch state
LED:
BOOT (red)
VBUS 5V
VBUS 5V
USB/UART
bridge:
FT231XQ-R
Balun:
BD0810J50100AHF
20 dB coupler:
DC1722J5020A
HF
Low pass filter:
0900LP15B0063
10 dB coupler:
DC1722J5020A
HF
TCXO:
TXEAADSANF-
20
Crystal:
(optional)
NX3225SA-20
Antenna
port 2
SMB Male
Antenna
port 1
SMB Male
6V
VBUS 5V
4
3
4
RF
Analog
RF switch:
SKY13431
-
374LF
PA LDO:
LD39100PUR
RX
MIX_INP
MIX_INN
MCU:
STM32L476RG
Power
a
mplifier:
TQP9107
Balun:
BD0810J50100AHF
Balun:
0900BL15C050
UHF RFID reader IC:
ST25RU3993

UM2742 Rev 1 9/44
UM2742 Hardware description
43
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.