The **u-blox SARA-R4 series** consists of LTE Cat M1, Cat NB1 (NB-IoT), and EGPRS modules designed for low-power wide-area (LPWA) IoT applications. They are known for their compact form factor and global multi-mode capabilities. --- ### 1. Key Internal Electronic Components The SARA-R4 architecture is built on a highly integrated SoC (System on Chip) platform. | Component | Description | | :--- | :--- | | **Baseband Processor** | Typically based on the Qualcomm MDM9206 or similar platforms, handling the LTE protocol stack. | | **RF Front-End** | Integrated power amplifiers and filters for global multi-band support (B1, B2, B3, B4, B5, B8, B12, B13, B18, B19, B20, B25, B26, B28). | | **Power Management (PMIC)** | Manages internal voltage rails to ensure ultra-low power consumption in Sleep and PSM modes. | | **Memory** | Integrated Flash and RAM to store the firmware and handle data buffering. | --- ### 2. External Interface Pins (LGA Package) The module uses a 96-pin LGA (Land Grid Array) package. Below are the primary electronic interfaces: #### Power Supply * **VCC:** Main power supply (typically 3.3V to 4.4V). * **V_INT:** Internal supply output for level shifters or small external pulls. #### Communication Interfaces * **UART:** The primary interface for AT commands and data transfer. (Includes RXD, TXD, RTS, CTS, DTR, DSR, DCD, RI). * **USB:** High-speed 2.0 interface for firmware updates and high-speed data. * **I2C:** For controlling external sensors or peripherals. * **GPIO:** General-purpose pins for status LEDs, waking up the module, or signaling events. #### RF Interface * **ANT:** 50 $\Omega$ pad for the cellular antenna. * **ANT_GNSS:** On specific models (like SARA-R412M), a dedicated pin for GPS/GLONASS. --- ### 3. Critical Specifications | Feature | Specification | | :--- | :--- | | **Form Factor** | 16.0 x 26.0 x 2.5 mm (LGA) | | **Voltage Range** | 3.2V to 4.2V (Nominal 3.8V) | | **Power Saving Mode (PSM)** | ~8 $\mu$A to 15 $\mu$A current draw | | **LTE Bands** | Multi-band (Global coverage) | | **Transmission Power** | Class 5 (20 dBm) or Class 3 (23 dBm) depending on variant | --- ### 4. Hardware Implementation Requirements When designing a PCB for the SARA-R4, pay attention to these electronic constraints: 1. **Decoupling Capacitors:** Place 100nF and 10$\mu$F capacitors close to the VCC pins to filter high-frequency noise and handle current spikes. 2. **RF Trace:** Use a 50 $\Omega$ coplanar waveguide or microstrip for the antenna path to prevent signal loss. 3. **Level Shifting:** The SARA-R4 I/O pins usually operate at 1.8V. If your MCU is 3.3V or 5V, you **must** use a bidirectional level shifter.