An Ultralow-Power Current-Reused Direct-Conversion Bluetooth-Low-Energy Receiver Front-End in 40-nm CMOS

An ultralow-power direct-conversion Bluetooth-low-energy (BLE) receiver (RX) front-end that employs current-reuse and subthreshold techniques is presented. A stacked and self-biased low-noise amplifier (LNA) with active balun consumes $400~\mu \text{W}$ and achieves a noise figure (NF) of 3.2-dB and a high gain (programmable from 18 to 31 dB), meeting the system specifications over the process, supply voltage, and temperature (PVT) variations. The RX front-end has a measured integrated NF of 5.2 dB from 50 KHz to 1 MHz that corresponds to a sensitivity of −95.1 dBm. At an RX gain of 47 dB, IIP3 was measured at −19.7 dBm. The LC VCO operates at twice the carrier frequency with a tuning range of 4.55 to 5.15 GHz in an integer-N phase-locked loop (PLL). An ultralow-power CML divider is used to generate the LO $I/Q$ . The integrated phase noise (IPN) of the LO at 2.4 GHz is 0.83° with spot phase noise of −119.9 dBc/Hz at 3 MHz frequency offset. The PLL is entirely placed inside the VCO inductor resulting in an overall die area reduction of 8%. A 6- $\mu \text{W}$ automatic dc offset-calibrator avoids saturation of consecutive baseband blocks. Multiple $\mu \text{W}$ -level feedback control loops are used in the design to make it robust over PVT variations. The RX front-end prototype is implemented in a 40-nm LP CMOS process and occupies a silicon area of 0.7 mm 2.