A 0.028% THD+N, 91% power-efficiency, 3-level PWM Class-D amplifier with a true differential front-end

Class D Amplifiers (CDAs) : PWM-in-PWM-out CDA, Filterless Bang-Bang CDA, and high-frequency high-efficiency CDA for Envelope Tracking

“…2-4(b), that the modulator in the analog CDA takes analog signal as the input and modulates it into a digital-like output signal. In general, the analog CDAs can be classified into four general types based on their different modulation schemes -Pulse Width Modulation (PWM) [15,19,20,24,54,55], Sigma-Delta Modulation [48,62,89], Bang-Bang Control [38,40,49,61,63] and Self-Oscillating [39,41,47,87,90,91]. They will now be reviewed in turn.…”

“…Interestingly, the Class D Amplifier (CDA) is a common circuit block as an audio amplifier and an amplifier to provide the varying supply voltage to the RF PA [2,[4][5][6][7][8][9][10][11]. In addition to power-efficiency considerations [12][13][14], contemporary audio-related electronic devices are also expected to feature high quality audio, if possible to high-fidelity standards [15] (e.g., qualified by Total Harmonic Distortion, THD [14,[16][17][18][19][20][21][22]), and in the presence of circuit noise (qualified by Power Supply Rejection Ratio, PSRR [19,21,[23][24][25][26][27]).…”

“…Of the various non-linearities, THD [14,[17][18][19][20][21][22] is arguably of the greatest interest because THD is typically quoted and generally easily perceived psycho-acoustically.…”

“…There are a number of reported modulation techniques for CDAs [17,40,41,[47][48][49][50][51][52][53]. Of these modulation techniques, the Pulse-Width-Modulation (PWM) is the most prevalent due to its high power-efficiency, hardware simplicity and superior performance [15,19,20,37,[54][55][56]. In a typical audio output system as depicted in Fig.…”

“…Nevertheless, the digital PWM may suffer some drawbacks arising from the fixed sampling moments, while digital PWM need not to be sampled at fixed intervals. [58,59] At this juncture, the design art [15,19,20,37,38,[54][55][56]60] for conventional PWM CDAs is relatively mature where the methodologies to mitigate their inherent relatively high non-linearities are well established. However, for the PIPO CDA where the input is a PWM signal, the investigations into its inherent non-linearities, including THD and PSRR, and methodologies to mitigate the said non-linearities remain largely unreported.…”