​Si4420 and Si4421 RF Transmitters​

Note: The Si4420 and Si4421 products are not available for new designs. For new designs, please use the Si4455 Sub-GHz Transceiver instead.
The Si4420/21 RF transmitters have a completely integrated PLL for easy RF design, and their rapid settling time enables fast frequency-hopping, bypassing multipath fading and interference to achieve very robust wireless links. The PLL’s high resolution allows the use of multiple channels in any of the bands. Highly stable and accurate FSK modulation is accomplished by closed-loop modulation with bit rates up to 256 kbps. In addition to the FSK modulation features, the microcontroller clock, wake-up timer, low battery detector, output power level and antenna tuning capability are also programmable through the serial interface.
*315 MHz band not available with Si4421


  • Fully integrated (low BOM, easy design-in)
  • Automatic antenna tuning circuit
  • No alignment required in production
  • Fast frequency-hopping capability
  • Fast-settling, programmable, high-resolution PLL synthesizer
  • High-bit rate (up to 115.2 kbps in digital mode and 256 kbps in analog mode)
  • Stable and accurate FSK modulation with programmable deviation
  • Direct loop antenna drive
  • Programmable output power level



  • SPI-compatible microcontroller interface
  • Power-saving sleep mode
  • Multiple event handling options for wake-up activation


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Data Sheet (2)

Si4420 Universal ISM Band FSK Transceiver
1.712/12/2008668 kB
Si4421 Universal ISM Band FSK Transceiver
2.412/12/20081463 kB

User Guides (2)

EZLink™ Fast Prototyping Modules—User Guide
0.111/25/20081753 kB
WDS Chip Configurator User Guide
0.24/9/20101416 kB

Application Notes (1)

White Papers (3)

Miscellaneous (1)

RF Wireless Foundation Course Book One
0.111/24/2008997 kB
Product Matrix
Part NumberOutput Power 868 MHzOutput Power 434 MHzSupply VoltagePackage TypeFSKDescriptionOOKSensitivityFrequency Bands
Si44202 dBm3 dBm2.2 - 5.4 VTSSOP16256 kbpsTRX315 MHz; 434 MHz; 868 MHz; 915 MHz
Si44217 dBm5 dBm2.2 - 3.8 VTSSOP16115 kbpsTRX434 MHz; 868 MHz; 915 MHz
    ​Note​: Supported for existing production, but not recommended for new designs. The Si4010 and Si4313 devices are recommended for new designs.


    Product Matrix





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