A Coin-Battery-Powered LDO-Free 2.4-GHz Bluetooth Low-Energy Transmitter With 34.7% Peak System Efficiency

Abstract

This brief reports a 2.4-GHz Bluetooth low-energy (BLE) transmitter (TX) that can operate against a coin-battery voltage discharging from 1.5 to 1 V, corresponding to a 99.2% battery capacity usage. Specifically, a class-B/C push–pull power amplifier with dual feedback control loops is proposed to dynamically adjust two gate biases, ensuring stable output power and low output HD2. The TX fabricated in 65-nm CMOS occupies a die area of 0.5 mm2 and achieves three stable power levels: $\text{P}_{{\mathbf{ out,H}}}$ (2.7 ± 0.4 dBm), $\text{P}_{{\mathbf{ out,M}}}$ (−0.1 ± 0.6 dBm), and $\text{P}_{{\mathbf{ out,L}}}$ (−2.5 ± 0.8 dBm). At $\text{P}_{{\mathbf{ out,H}}}$ , the system efficiency reaches 34.7%. The 1-Mb/s GFSK output ( ${\mathbf{ m = 0.5}}$ ) and HD2,3 comply with the BLE specifications, and the FSK error is 8.2%. A tiny demo board with an antenna, a crystal, and a coin battery (Nanfu LR44) verifies the feasibility of the TX over-the-air, achieving 27.5 h of continuous operation for a 1-dB reduction of the received power.