Abstract
In this paper a class-D smart speaker driver is presented 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 embedded DSP. The protection algorithm estimates the membrane excursion and voice coil temperature using a speaker model that tracks the speaker impedance which 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 the instantaneous load current equals the average current. At full output power the combined efficiency of the class-D amplifier 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.
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