Filterless multi-level delta-sigma class-D amplifier for portable applications

Bandwidth extension techniques for high-efficiency power amplifiers

“…In either case, this technique based on enhanced decoding logic and switching policy allows controlling the commonmode voltage regardless of the modulation; furthermore, it does not require any additional power resources and neither the efficiency nor the tracking fidelity is affected. Similar approaches have also been reported in the literature [52], but constrained to a specific modulator and implementation; other approaches reported in the literature require additional power resources (described in section 1.5.3).…”

“…These designs are based on a high-order Σ∆ modulator (generally mixing both continuous-time and discrete-time implementations), which generates a high-frequency 1-bit datastream. By upgrading the quantiser to multiple levels, multi-level amplification is achieved [52]. In order to control (reduce, in this case) the switching frequency, the hysteresis width of the quantiser is dynamically adapted using a slow control loop (the dynamics of this loop and hence the dynamics of the hysteresis width are much slower than the reference signal's dynamics), so that the average switching frequency is the desired one [53].…”

“…Regarding the common-mode issue in filterless audio amplifiers, a technique to partially shape the waveform of the common-mode voltage signal was recently reported in the literature [52]. This technique consists in using a control loop to determine how the zero level is generated (either by driving both sides of the full-bridge converter to GN D or to the supply voltage V G ).…”

“…both ends of the low-pass filter's input port) to the same voltage level, either GN D or V G . With an appropriate policy, this redundancy can be used to shape the common-mode voltage to high frequency [52] (this is further analysed in section 6.2).…”