A Design of Analog PLL-Based Self-Calibrated Open-Loop FSK Modulator for BLE Advertising Transmitter

This brief presents a self-calibrated open-loop modulation technique for a Bluetooth low energy (BLE) advertising transmitter. The proposed technique can be implemented using a voltage-controlled oscillator (VCO), counter, and capacitor for voltage storage in an analog phase-locked loop (PLL). In the closed-loop mode using negative feedback, the VCO generates the target frequency output, and the control voltage of the VCO is stored in the capacitor. In the proposed open-loop mode, the stored control voltage is fed to the VCO. The frequency offset caused by the voltage offset is measured using a counter and corrected using the modulation capacitor bank of the VCO together with the frequency deviation. Thus, the open-loop modulation approach does not necessitate the use of additional circuits for detecting and compensating frequency offsets. The proposed open-loop modulation consumes 600 \, \mu \text{W} less power than the closed-loop modulation and has been implemented using the 55-nm CMOS process. The chip area is 0.225 mm2, and the total power consumption is 1.22 mW.