Power Supply Noise in Analog Audio Class D Amplifiers

Abstract

A potential drawback of class D amplifiers (CDAs) is their relatively poor tolerance to power supply noise. It has been recently established by means of a linear model that the manifested nonlinearities due to the supply noise are the fundamental noise frequency component and second-order intermodulation components, qualified by the power supply rejection ratio (PSRR) and intermodulation distortion (IMD), respectively. In this paper, multidimensional Fourier series analysis is applied to open-loop, single-, and double-feedback pulsewidth modulation CDAs, and expressions for PSRR, IMD, and fold-back distortion (FBD) are derived. This analysis takes into account the nonlinear pulse modulation process (unaccounted for in the linear model), and all components of PSRR and IMD nonlinearities are hence modeled. It is shown that the first-harmonic PSRR and third-order IMD components, which are usually ignored in CDAs and linear amplifiers, are significant and that, under certain conditions, the third-order IMD components can be higher than the second-order IMD components. It is also shown that the loop gain should be high for high PSRR and low IMD. Furthermore, significant FBD can arise due to the intermodulation between the supply noise, the input signal, and the carrier, and interestingly, the FBD in closed-loop CDAs is more serious than that in open-loop CDAs. The analyses herein are verified by computer simulations and on the basis of measurements on a prototype CDA IC and on other hardware realizations.

Modeling based on Elman Wavelet Neural Network for Class-D Power Amplifiers

“…It is known that these phenomena come from the memory effects [7], which means that the output depends not only on the input signal at the moment but also on the history of past input levels. Adding a sinusoidal power ripple to the power supply of the open-loop CDPA circuit, the expression of the PWM signal before the low-pass filter is given in [4]. It shows that the PS-IMD should be symmetrical in the output signal.…”

A 15nV/√Hz noise 0.2μV offset chopper conditioning amplifier for monolithic infrared sensing systems

“…Infrared (IR) sensing systems are widely employed in various commercial and military applications including photography, video & audio systems [1,2], security devices, night-vision, etc. In a general IR sensing system, an IR sensor senses the IR radiation and outputs a photovoltage signal, and Read-Out Integrated Circuit (ROIC) subsequently conditions the photovoltage signal and provides amplification.…”

A novel high-fidelity analog class-D amplifier based on self-oscillation for earphones/headphones

“…At this juncture, the FBD in CDAs is not well understood, remains unreported and the mechanisms thereof are unknown. According to our research group [40], FBD is less significant in the amplifier with higher carrier frequency (>250 kHz).…”

“…Note that in conventional PWM CDA, the comparator loop gain is typically 6-10dB [40] This is largely because the triangular carrier applied to the PWM CDA (Vp is ~VDD/2 or VDD/3) has larger amplitude than the amplitude in selfoscillating CDA (Vp is in the range of tens of mV and << VDD (5V)). Thus, by applying equation 3-7, the comparator loop gain can be estimated and the loop gain of the PWM is generally much smaller (50-60dB) than that of the selfoscillating CDA.…”