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We propose a novel low-harmonics low-noise modulation scheme for switched-mode dc–dc converters. The proposed scheme is a hybrid of a randomized modulation scheme, namely, the randomized wrapped-around pulse position modulation scheme (RWAPPM), and a noise-shaper. The RWAPPM mitigates the switching-frequency harmonics in the input current, whereas the noise-shaper mitigates the low-frequency noise therein. We derive an analytical expression for the input current spectrum of the hybrid scheme. We benchmark the hybrid scheme against the conventional pulse width modulation scheme (PWM) and the RWAPPM without the noise-shaper. At 0.5 duty cycle, 3.3-V input voltage, 100-kHz average switching frequency, and with the second-order noise-shaper, the peak spectral power in the input current spectrum of the hybrid scheme is 18.1 dB lower than the PWM. Other randomized and spread-spectrum modulation schemes, in general, have undesirably higher input noise current than that of the PWM. However, the input noise current of the proposed hybrid scheme, obtained at ~73-mA rms (integrated over a 200-kHz bandwidth without an input filter), is comparable with that of the PWM, and is lower by ~16-mA rms compared with that of the RWAPPM without the noise-shaper. We also benchmark the hybrid scheme against other well known randomized and spread-spectrum modulation schemes. We further propose a novel pulse generator structure that embodies the hybrid scheme. We realize a dc–dc converter employing the pulse generator, and measure the converter to verify the derived expression and the characteristics of the hybrid scheme. We also measure the output voltage spectrum, the transient-response, and the operating range of the converter. [ABSTRACT FROM PUBLISHER]

We present a novel randomized wrapped-around pulse position modulation (RWAPPM) scheme for digital modulators of dc–dc converters. Unlike the reported modulation schemes that require a varying switching period (thereby resulting in high attenuation or complete elimination of discrete harmonics), the proposed RWAPPM conversely requires only a constant switching period (thereby advantageous in terms of easy realization in hardware), and yet, its discrete harmonics are negligible. We derive an expression for the spectrum of the RWAPPM scheme to analytically obtain the peak spectral power and ripple noise voltage of RWAPPM. This expression further provides insight to the parameters that influence the RWAPPM spectrum. We benchmark the RWAPPM scheme against the ubiquitous conventional pulsewidth modulation scheme and six reported (randomized and frequency modulation) schemes. The RWAPPM scheme features negligible discrete harmonics [\leq -158 dB relative to full scale (dBFS)], and among the modulation schemes, it features the lowest peak spectral power at -26.6 dBFS (before low-pass filtering) and relatively low ripple noise at 2 mVrms (after low-pass filtering) for a 3.6–2.5-V conversion and an effective switching frequency of 120 kHz. We verify the derived expression and attributes of the RWAPPM spectrum by computer simulations and on the basis of experimental measurements on a dc–dc converter. [ABSTRACT FROM PUBLISHER]

We present a micropower digital modulator for class-D amplifiers for power-critical digital hearing aids. The modulator design embodies a proposed Lagrange interpolation (a combined first- and second-order Lagrange) algorithmic pulsewidth modulation (PWM) and a third-order ΔΣE noise shaper. By means of double-Fourier-series analysis, we analyze and determine the harmonic nonlinearities of the proposed algorithmic PWM. At 48-kHz sampling, 96-kHz PWM output, 997-Hz input, and input modulation index = 0.9, the modulator circuit achieves a total harmonic distortion + noise (THD + N) of -74 dB (0.02%) over an 8-kHz voice bandwidth-a 12-dB THD + N improvement over a reported design and yet dissipates only ∼50% of the power. The proposed modulator dissipates the lowest power dissipation of all modulators compared, and by means of a proposed figure of merit, the proposed modulator exhibits very competitive performance. The modulator IC is fabricated in a 0.35-μm digital CMOS process with a core area of 0.46 mm². [ABSTRACT FROM AUTHOR]

A digital Class-D amplifier comprises a pulsewidth modulator (PWM) and an output stage. In this paper, we simplify the time-domain expression for the algorithmic PWM linear interpolation (LI) sampling process and analytically derive its double Fourier series expression. By means of our derivation, we show that the nonlinearities of the LI process are very low, especially given its modest computation complexity and low sampling frequency. In particular, the total-harmonic distortion (THD) ≈0.02 % and fold-back distortion is -98.4 dB (averaged from modulation indexes M = 0.1 to 0.9) for the 4-kHz voiceband bandwidth @1-kHz input, 48-kHz sampling. We also describe a simple hardware for realizing the LI process. We propose a frequency doubler (with small overheads) for the pulse generator for the PWM, thereby reducing the counter clock rate by 2, leading to a substantial r.∼47% power dissipation reduction for the Class-D amplifier. By means of computer simulations and on the basis of experimental measurements, we verify our double Fourier series derivation and show the attractive attributes of a Class-D amplifier embodying our simplified LI sampling expression and reduced clock rate pulse generator. We show that our Class-D amplifier design is micropower (∼60 μW @1.1 V and 48-kHz sampling rate, and THD ≈0.03%) and is suit- able for practical power-critical portable audio devices, including digital hearing aids. [ABSTRACT FROM AUTHOR]