A Low Power Bluetooth Low-Energy Transmitter with a 10.5nJ Startup-Energy Crystal Oscillator

Abstract

This paper presents a low power, fully-integrated Bluetooth Low-Energy (BLE) transmitter (TX) for Internet-of-Things (IoT) applications. The complete BLE TX achieves a total energy per bit of 3.5nJ in an open-loop transmission scheme due to the ultra-low startup energy of the system. The overall system architecture of the BLE TX includes an RF front-end, a 16 MHz crystal oscillator (XO), a GFSK modulator, and a digital baseband including a SPI interface. An enhanced capacitively loaded three-stage inverter chain XO is proposed, featuring a 10.2nJ startup-energy, a 150μs startup time, and a 70μW steady-state power. The steady-state frequency inaccuracy of the XO is 14 ppm with less than 26ps cycle-to-cycle jitter. The BLE TX is fabricated in 65nm CMOS technology and it consumes an average power of 2.17mW to transmit an advertisement packet consisting of 368 bits entirely over 600μs including the startup time. Duty-cycling operation is implemented through power gating achieving an average power consumption of 3.72μW (1.86× sleep power) when transmitting a BLE advertising message every 753ms. In our target application, by using these techniques, we are able to extend a common coin battery’s lifetime to more than 20 years.