Open-Source Fully-Synthesizable ADPLL for a Bluetooth Low-Energy Transmitter in 12nm FinFET Technology

Abstract

In this work, we present an open-source fully-synthesizable fractional-N ADPLL designed for a Bluetooth Low-Energy (BLE) transmitter (TX). A highly automated design flow is used to lower the barrier for new developers and to reduce porting cost. In the PLL, a novel two-step TDC (TSTDC) is proposed, which is amenable to P&R, and uses an embedded TDC (EMBTDC) and vernier delay-line TDC (DLTDC) as coarse and fine TDCs, respectively. This combination reduces the required DLTDC input time range by 5x and is used to measure and compensate the P&R induced non-linearity of the EMBTDC. The PLL is fabricated in 12-nm FinFET and demonstrated in a BLE-TX. BLE transmissions satisfy the standard requirements thanks to the reduced fractional spurs by abovementioned techniques. In a standalone PLL mode, the TSTDC reduced fractional spurs by 6.8 dB compared to an EMBTDC alone, and the proposed LUT-based calibration further reduced spurs by 7.5 dB in near-integer operation. The PLL supports frequency range of 1.8-2.7GHz and consumes 3.91mW at 2.4006 GHz, with a 40MHz reference, occupying area of 0.063mm2.