Ways to suppress click and pop for class D amplifiers

Undesirable audio click and pop may be generated in a speaker or headphone.Compared to linear（class A/B/AB） amplifiers,class D amplifiers that comprise of an input stage and a modulation stage are more prone to producing click and pop.This article analyzes sources that generate click and pop in class D amplifiers,and corresponding ways to suppress them.For a class D amplifier with a single-ended input,click and pop is likely to be due to two factors.One is from a voltage difference（KDIF） between the voltage of an input capacitance（Vcin） and a reference voltage（Vref） of the input stage,and the other one is from the non-linear switching during the setting up of the bias and feedback voltages/currents（BFVC） of the modulation stage.In this article,a fast charging loop is introduced into the input stage to charge F_（CIN） to roughly near VREF.Then a correction loop further charges or discharges V_（CIN）,substantially equalizing it with KREF.Dummy switches are introduced into the modulation stage to provide switching signals for setting up BFVC,and the power switches are disabled until the BFVC are set up successfully.A two channel single-ended class D amplifier with the above features is fabricated with 0.5μm Bi-CMOS process.Road test and fast Fourier transform analysis indicate that there is no noticeable click and pop.

A 0.02% THD and 80 dB PSRR filterless class D amplifier with direct lithium battery hookup in mobile application

This paper presents a fully integrated CMOS filterless class D amplifier that can directly hook up lithium battery in mobile application The proposed amplifier embodies a 2-order feedback path architecture instead of direct feedback of output to input of the integrator to decrease the high frequency intermodulation distortion associated with direct feedback and eliminate the integrator input common mode disturbance from the output in ternary modulation. The prototype class D amplifier realized in 0.35 μm digital technology achieves a THD＋N of 0.02% when delivering 400 m W to an 8 Ω load from V_（DD） =3.6 V. The PSRR of the prototype class D amplifier is 80 dB at217 Hz. Furthermore a filterless method that can eliminate the external LC filter is employed which offers great advantages of saving PCB space and lowering system cost. In addition the prototype class D amplifier can operate in large voltage range with V_（DD）range from 2.5 to 4.2V in mobile application. The total area of the amplifier is 1.7mm^2.

Design of low noise class D amplifiers using an integrated filter

This paper investigates the noise sources in a single-ended class D amplifier（SECDA） and suggests corresponding ways to lower the noise.The total output noise could be expressed as a function of the gain and noises from different sources.According to the function,the bias voltage（V_B） is a primary noise source,especially for a SECDA with a large gain.A low noise SECDA is obtained by integrating a filter into the SECDA to lower the noise of the V_B.The filter utilizes an active resister and an 80 pF capacitance to get a 3 Hz pole.A noise test and fast Fourier transform analysis show that the noise performance of this SECDA is the same as that of a SECDA with an external filter.

An advanced monolithic digitalized random carrier frequency spread-spectrum clock generator for EMI suppression

A novel monolithic digitalized random carrier frequency modulation spread-spectrum clock generator （RCF-SSCG） is proposed.In this design,the output frequency of the proposed RCF-SSCG changes with the intensity of the capacitive charge and discharge current.Its analytical model is induced and the effect of the modulation parameters on the spread spectrum is numerically simulated and discussed.Compared with other works,this design has the advantages of small size,low power consumption and good robustness.The circuit has been fabricated in a 0.5μm CMOS process and applied to a class D amplifier in which the proposed RCF-SSCG occupies an area of 0.112 mm^2 and consumes 9 mW.The experimental results confirm the theoretical analyses.