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
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: 30 dBm max. TX power
–Internal PA: 17.5 dBm max. TX power
Configurable TX power level
Power detector to monitor TX power
Automatic carrier cancellation for improved RX sensitivity
Differential RX input
RX sensitivity:
–-80 dBm at 90% read success, one sideband of tag response (ISO18046-3: 2012)
–-77 dBm at 90% read success, both sidebands of tag response
(ISO18046-3: 2020)
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
UM2742 Rev 25/44
43
Standard connection setupUM2742
Two antenna ports: SMB (M)
Automatic / Manual antenna port switching
Carrier sense TX option (LBT)
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
–LED indicators
–Power amplifier selection
–Carrier cancellation tuning activity
–Carrier cancellation tuning OK
–OSC OK (20 MHz external reference)
–PLL OK
–RF ON
–No tag response
–Tag CRC error
–Tag found
Test points:
–In-circuit RF power levels and signals
a. Arm is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.
6/44UM2742 Rev 2
UM2742Standard connection setup
–RFID communication TX and RX
–UART and SPI signal lines
–UART_LOG for debugging purposes
–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
UM2742 Rev 27/44
43
Standard connection setupUM2742
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
Figure 3. ST25RU3993-HPEV functional diagram
8/44UM2742 Rev 2
UM2742Hardware 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 Tabl e 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.
TCXO connected to ST25RU3993Crystal connected to ST25RU3993
R54 and R55 not populatedC51 removed, R54 and R55 populated
Table 1. TXCO / Crystal configuration
DefaultAlternate (modified by user)
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.
UM2742 Rev 29/44
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Hardware descriptionUM2742
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
stage of the low power output is supplied by the V
DD_B
Ω single-ended signal. The output
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
Ω single-ended signal. The internal power amplifier is supplied by the on-chip generated
and regulated voltage V
. L1, L2 are acting as RF chokes, C12 and C14 are bypass
DD_PA
capacitors. After the balun the output power of the internal power amplifier is tipically
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.
10/44UM2742 Rev 2
UM2742Hardware description
Figure 4. Power detector voltage characteristics
The DC output voltage of the power detector is connected to an ADC input pin (PA1) of the
microcontroller.
The majority of RF transmit power which passes through the 20 dB directional coupler is fed
to the main directional coupler. The main directional coupler has a coupling factor of 10 dB
and acts as the directional unit which should isolate the transmit from the receive path of
ST25RU3993. The main directional coupler plays a very important role in the RFID reader
system as its parasitics have a great influence on the sensitivity of the reader. The main
directional coupler essentially has four terminals:
1. Input
2. Direct
3. Coupled
4. Isolated
The direct terminal is connected to the second RF switch in the reader system. This switch
directs the transmit power to either antenna port 1 or antenna port 2. The antenna switch
again requires DC blocking capacitors on all its RF terminals. Both antenna ports are SMB
(male) type.
To avoid reducing the sensitivity of the reader the self-jamming signal reaching the receiving
inputs of ST25RU3993 must be minimized. The self-jamming signal comprises reflections
from the antenna (S11) and the leakage across the main directional coupler. To minimize it a
carrier cancellation circuit is connected to the coupled port of the main directional coupler.
UM2742 Rev 211/44
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Hardware descriptionUM2742
The carrier cancellation circuit is able to change its impedance and hence to reflect a certain
amount of the coupled power back into the directional coupler. This reflected signal is
combined with the self-jamming signal at the isolated port of the main directional coupler.
The isolated port of the main directional coupler is connected to the receiving pins of
ST25RU3993. If the signal reflected by the carrier cancellation circuit has the same
amplitude and opposite phase of the self-jammer the signals cancel them out and vanish.
The main components of the CCC are three digital tunable capacitors controlled by the
STM32L476RG microcontroller via SPI. The lumped components of the carrier cancellation
circuit help to define its tuning range around 50
Ω and define the impedance step created by
one LSB change of a digital tunable capacitor.
The isolated port of the main directional coupler is connected to a 2:1 balun to transform the
incoming tag response signal to a 100
Ω differential signal that is fed into ST25RU3993
receiver section at pins MIX_INP (4) and MIX_INN (6).
Table 2. MCU interfaces and buttons (see Figure 5)
®
32-bit Cortex®-M4)
12/44UM2742 Rev 2
UM2742Hardware description
MS53587V1
A
B
C
O
P
F
K
L
N
M
D
E
J
H
G
Figure 5. Main digital interfaces
The ST25RU3993-HPEV is controlled by STM32L476RG, a ultra-low-power MCU with FPU
Arm Cortex-M4 core, 80 MHz, 1 Mbyte Flash memory, LCD, USB OTG, DFSDM.
UM2742 Rev 213/44
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Hardware descriptionUM2742
The MCU is supplied by 3.3 Volts, regulated by an adjustable LDO. The clock source is an
external crystal generating 32.768 kHz, connected to OSC32_in (3) and OSC32_out (4). It
interfaces the host PC via UART for which a USB/UART bridge is used.
The MCU communicates with the ST25RU3993 via an SPI interface controlling the
ST25RU3993 lines ENABLE and IRQ. The SPI interface operates in mode 1 with a 6 MHz
serial clock. The SPI interface is also used to control the digital tunable capacitors for the
carrier cancellation circuit.
The MCU controls the RF switches for changing the power amplifier and the active antenna
port. The analog output of the RF power detector is connected to one of its ADC inputs
(PA1) to convert the DC voltage corresponding to the transmit RF power into a digital
representation. The LDO for the external power amplifier is enabled by the MCU, making it
possible to completely shut down the external power amplifier when RF power needs to be
OFF, e.g. as required for carrier sense (LBT). One pin (UART LOG) is reserved to act as a
generic debug pin or to be programmed as a trigger output for an external measurement
equipment.