A4 Ω 2.65W Class-D Audio Ampli fier With Embedded DC-DC Boost Converter, Current Sensing ADC and DSP for Adaptive

Abstract

In this paper a class-D smart speaker driver is pre- sented that can deliver 2.65 W at 1% THD into a 4Ω load. Maximal output power is maintained at low battery voltage by supplying the class-D amplifier from a DC-DC boost converter. Speaker damage is avoided by a speaker protection algorithm that runs on an em- bedded DSP. The protection al gorithm estimates the membrane excursion and voice coil temperature using a speaker model that tracks the speaker impedance whi ch is determined by measuring the speaker current with less than 2% relative error. A sample & hold technique is presented that rejects the load current ripple by sampling at the moments where t he instantaneous load current equals the average current. At full output power the combined efficiency of the class-D ampli fier and DC-DC boost converter is higher than 80%. The complete system is implemented on a single chip that measures 6.6 mm² and is fabricated in a 0.14 µm CMOS technology with a 5 V gate-oxide option.