PLL Fractional Spurs Impact on FSK Spectrum and a Synthesizable ADPLL for a Blue

Abstract

In this work, we present an open-source fully- synthesizable fractional-N all-digital phase-locked loop (ADPLL) designed for a Bluetooth low-e nergy (BLE) transmitter (TX) along with a semi-analytical model of the PLL fractional spur’s impact on the BLE output spectrum. Based on the model and the BLE specification for spur emission, a requirement for the PLL fractional spurs is derived. To meet the derived spectral mask by reducing the fractional spurs, a novel synthesizable two-step time to digi