Envelope Tracking DC-DC Power Supply for a Piezoelectric MEMS-Based Earbuds System

An energy-saving Envelope Tracking (ET) circuit, which is part of an integrated system for Bluetooth Ear-buds, is presented in this paper. The full system is composed of a piezoelectric Micro- Electro- Mechanical Systems (MEMS) speaker, a Fully Differential Class-AB Power Amplifier (PA) to drive the speaker and a digital front-end, all powered by a power management circuit. The ET architecture is based on two primary blocks: a switched capacitor circuit and a dynamic latch comparator. Whenever the output signal value of the PA reaches the supply voltage value, the comparator sends a control signal to the logic of the full system, which then modulates the supply voltage in order to keep this as low as possible, minimizing power consumption. The circuit has been implemented at the transistor level employing a BCD 180 nm technology. The simulated power consumption of the ET block is lower than 100 µW.