9. Radio system

9.1 Introduction

The 2.4 GHz RADIO is ultralow power, operating in the 2.4 GHz ISM band. It provides Bluetooth® Low Energy 1 Mbps coded, 1 Mbps, and 2 Mbps noncoded GFSK, and IEEE802.15.4 chip rate 2 Mchip/s, spreading mode DSSS, data rate 125 and 250 kbps O-QPSK-C modulation.

The 2.4 GHz RADIO is compliant with the Bluetooth and Zigbee® specifications, and radio regulations including ETSI EN 300 328, EN 300 440, EN 301 489-17, ARIB STD-T66, FCC CFR47 part 15 section 15.205, 15.209, 15.247, and 15.249, IC RSS-139 and RSS-210.

9.2 Main features

• Radio protocol:
- – Bluetooth® Low Energy
- – IEEE802.15.4
• Bluetooth® Low Energy features:
- – Device privacy and network privacy modes
- – Anonymous device address types
- – Advertising extension PDUs
- – Advertising channel index
- – Periodic advertising synchronous transfer
- – High duty cycle, nonconnectable advertising
- – Channel selection algorithm #2
- – Angle of arrival (AoA), angle of departure (AoD)
- – Channel sounding
- – Up to eight connections in any role in addition to advertiser and scanner roles
- – Audio connected isochronous streams
- – Audio broadcast isochronous streams
• IEEE 802.15.4 features:
- – Beacon management
- – 16-bit short and 64-bit IEEE addressing modes
- – PAN formation along with association and disassociation
- – Full handshake protocol for transfer reliability, frame validation, and acknowledgment frame delivery
- – IEEE802.15.4 2020 MAC for nonbeaconed PANs
• External PA support
• Packet traffic arbitration

9.3 2.4 GHz RADIO implementation

Table 81. Radio features

Feature ⁽¹⁾	STM32WBA 25xx	STM32WBA 23xx
Bluetooth (1 Mbps and codec PHY)	X	X
Bluetooth (2 Mbps)	X	X
Bluetooth AoA/AoD	X	X
IEEE802.15.4	X	X
Transmit maximum output power	+10 dBm
External PA	X	X
Packet traffic arbitration	X	X

1. X = supported.

9.4 Functional description

9.4.1 Block diagram

Figure 23. Radio system block diagram

VDDANA is available only on packages with SMPS. On LDO packages VDDANA is double bonded with VDDRF.

MS66759V1

Figure 23. Radio system block diagram. The diagram shows the internal architecture of the 2.4 GHz RADIO. On the left, the 'Low Layer Protocol' block is connected to the AHB bus, RXTXRAM, and SEQRAM. It has control inputs for RADIO interrupt, External PA control, AoA/AoD and channel sounding antenna control, PTA interface, 2.4 GHz RADIO kernel clock, and Sleep timer clock. It has output signals for Rx (to Demodulator) and Tx (to Modulator). The Modulator output goes to an LF (Low Frequency) block, which is connected to a PFD/CP (Phase Frequency Detector/Charge Pump) and a DIV (Divider). The PFD/CP is connected to the 2.4 GHz RADIO RF clock. The LF block output goes to a mixer. The Demodulator output goes to an I (In-phase) and Q (Quadrature) block, which is connected to a BPF (Band Pass Filter). The BPF output goes to a mixer. The mixer output goes to an LNA (Low Noise Amplifier). The LNA output goes to a Matching block. The Matching block is connected to the RF pin and has control inputs for VDDRF, VDDANA, VDDRFPA, and VDDHPA. The RF pin is connected to the external RF input/output. The diagram is labeled '2.4 GHz RADIO'.

9.4.2 Pins and internal signals

Table 82. Input/output pins

Pin name	Signal type	Description
RF	RF	2.4 GHz RF input output
RADIO interrupt	Output	2.4 GHz RADIO interrupt to the CPU
External PA control	Output	External PA control

Table 82. Input/output pins (continued)

Pin name	Signal type	Description
AoA/AoD antenna control	Output	Angle of arrival/departure antenna area control
PTA interface	Input/Output	Packet traffic arbitration control

9.4.3 Transmit output power

The 2.4 GHz RADIO includes an internal PA. The transmit output power can be increased using an additional external PA. External PA control signal BYPASS can be selected on GPIOs (see the datasheet), and the signal ENABLE can be mapped on any free GPIO by the application software. The polarity of the BYPASS signal is selected in SYSCFG.

Figure 24 shows the transmit path and output power control.

Figure 24. Transmit path and output power control

Figure 24: Transmit path and output power control diagram. The diagram shows the internal transmit path of a 2.4 GHz RADIO. A 'Transmit output power dBm' input goes to a 'PA output power table', which outputs 'VDDHPA level', 'PA code', and 'RF_EXTABYP'. The 'PA code' goes to an 'int PA' (internal Power Amplifier). The 'VDDHPA level' goes to a 'REG VDDHPA' block, which also receives 'PWR_RADIOSCR.REGPASEL' and 'PWR_RADIOSCR.REGPABYPEN' signals. The 'REG VDDHPA' outputs 'VDDHPA' to the 'int PA'. The 'int PA' outputs 'TX' to an 'RF' block. The 'RF' block outputs 'TX/RX' to an 'External PA (optional)'. The 'External PA' outputs 'PA' to an 'Antenna'. The 'External PA' also receives 'BYPASS' and 'ENABLE' signals. The 'BYPASS' signal comes from 'GPIO[n] (optional)' and the 'ENABLE' signal comes from 'GPIOx[y] (optional)'. The 'GPIO[n] (optional)' and 'GPIOx[y] (optional)' signals are controlled by 'SYSCFG polarity' and 'GPIO AF mapping' blocks. The 'SYSCFG polarity' block receives 'RF_EXTABYP' from the 'PA output power table'. The 'GPIO AF mapping' block receives 'PA code' from the 'PA output power table'. The 'VDDHPA' signal also goes to 'VDDRFPA' and 'VDD11(1)' blocks. The 'VDDRFPA' block outputs 'VDDRFPA' to the 'int PA'. The 'VDD11(1)' block outputs 'VDD11(1)' to the 'int PA'.

1. VDD11 must be selected only when supplied from device SMPS.

The transmit output power (in dBm) is dependent upon the V _DDHPAvoltage level and the PA code, and, when the application supports an external PA, an external PA bypass indication. The values for these parameters are defined in a PA output power table available to the Link Layer software.

Table 83. PA output power table format

V _DDHPAlevel	PA code	BYPASS
0x0 = 0.90 V	0 to 25 dec.	0 or 1
0x1 = 0.95 V
0x2 = 1.0 V
0x3 = 1.1 V
...
0xE = 2.2 V
0xF = 2.3 V

The internal PA maximum transmit output power is depended upon the $V_{DDHPA}$ voltage level and the PA code. The maximum $V_{DDHPA}$ voltage level is dependent upon the application (VDDRFPA pin) supply scheme, see Table 84 for details. Note that the 2.4 GHz RADIO internal $V_{CCRF}$ regulated supply level also depends upon the VDDRFPA pin supply scheme:

• If $V_{DDRFPA} < 1.71$ V, the $V_{CCRF}$ regulated supply level must be 1.0 V.
• If $V_{DDRFPA} \geq 1.71$ V, the $V_{CCRF}$ regulated supply level must be 1.2 V.

The REG VDDHPA regulator input voltage can be controlled through REGPASEL and REGPABYPEN.

Table 84. 2.4 GHz RADIO supply configuration

$V_{DDHPA}$ level	Minimum $V_{DDRFPA}$	Internal PA max transmit output power
1.0 V	1.2 V ⁽¹⁾	+ 3 dBm
1.2 V	1.71 V	+ 6 dBm
1.5 V	1.8 V	+ 8 dBm
2.3 V	2.6 V	+ 10 dBm

1. Only on STM32WB25xx devices, when SMPS is used.

9.4.4 Bluetooth AoA/AoD and channel sounding antenna selection

Up to eight antennas are supported by means of the coded RF_ANTSW[2:0] signal bus available through GPIO alternate function for Bluetooth AoA when receiving the constant tone extension of a packet, or for AoD while transmitting the constant tone extension of a packet. Up to four antennas are supported with channel sounding.

Figure 25. Bluetooth AoA/AoD antennas control

Figure 25: Bluetooth AoA/AoD antennas control diagram. The diagram shows the internal architecture of the 2.4 GHz RADIO. It includes a TX path with an internal PA and a Matching block, and an RX path with an LNA and a Matching block. The RF_ANTSW[2:0] signal bus is connected to the Matching blocks. The RF output is connected to an Antenna matrix (optional) via a TX/RX switch. The Antenna matrix is controlled by a Control block with inputs V1, V2, and V3. The Control block is connected to GPIOx, GPIOy, and GPIOz pins via an AF mapping block. The Antenna matrix outputs are labeled Antenna1 through Antenna8.

9.4.5 RXTX data SRAM access

For the host application to access the 2.4 GHz RADIO RXTXRAM, the Link Layer software must put the 2.4 GHz RADIO in Sleep mode. When access to the 2.4 GHz RADIO RXTXRAM is no longer needed by the host application, it must request the Link Layer software to put the 2.4 GHz RADIO in Deep sleep mode.

To access the RXTX data SRAM, both the 2.4 GHz RADIO bus clock and kernel clock must be active and ready.

The 2.4 GHz RADIO modes depend both on the host application request and the Link Layer scheduled radio activity.

9.5 Low-power modes

The 2.4 GHz RADIO supports autonomous operation down to Stop 0 mode voltage scaling range 1 and 1.5, and the 2.4 GHz RADIO configuration and sleep timer remains operational down to Standby retention mode.

The 2.4 GHz RADIO in autonomous mode (Active mode) is able to transmit and receive packets over the air for the radio connection.

The 2.4 GHz RADIO configuration SRAMs and sleep timer allows to maintain radio connections when the radio is in low-power mode (Sleep and Deep sleep mode), this i.e. in between the Bluetooth LE connection events.

The 2.4 GHz RADIO must be disabled before entering Standby mode.

Table 85. Effect of low-power modes on the 2.4 GHz RADIO

Mode	Description
Sleep	No effect. 2.4 GHz RADIO (only in voltage scaling range 1) and 2.4 GHz RADIO sleep timer interrupts cause the device to exit Sleep mode. Radio connection are maintained and may transmit and receive.
Stop 0 voltage scaling range 1 and 1.5	The 2.4 GHz RADIO will autonomously transmit and receive packets, 2.4 GHz RADIO and 2.4 GHz RADIO configuration and sleep timer interrupts cause the device to exit Stop 0 mode. Radio connection are maintained and may transmit and receive.
Stop 0 voltage range 2 and Stop 1, and Stop 2	The 2.4 GHz RADIO configuration is retained but is no longer capable to transmit and receive packets, The 2.4 GHz RADIO sleep timer interrupt cause the device to exit Stop mode. Radio connection are maintained during i.e. the Bluetooth LE connection interval.
Stop 3	The 2.4 GHz RADIO and the 2.4 GHz RADIO sleep timer are no longer operational. Radio connection are lost.
Standby retention	The 2.4 GHz RADIO configuration is retained but is no longer capable to transmit and receive packets, The 2.4 GHz RADIO sleep timer interrupt cause the device to exit Standby retention mode. Radio connection are maintained during i.e. the Bluetooth LE connection interval.
Standby	The 2.4 GHz RADIO and 2.4 GHz RADIO sleep timer are powered down. Radio connection are lost.