A 28-W, −102.2-dB THD+N Class-D Amplifier Using a Hybrid ΔΣM-PWM Scheme

Abstract

This paper presents a 28W Class-D amplifier for automotive applications. The combination of a high switching frequency and a hybrid multi-bit ∆ΣM-PWM scheme results in high linearity over a wide range of output power, as well as low AM-band EMI. As a result, only a small (150kHz cutoff frequency), and thus low-cost, LC filter is needed to meet the CISPR-25 EMI average limit (150kHz-30MHz) with 10dB margin. At 28W output power, the proposed amplifier achieves 91% efficiency while driving a 4Ω load from a 14.4V supply. It attains a peak THD+N of 0.00077% (-102.2dB) for a 1kHz input signal.

A Chopper Class-D Amplifier for PSRR Improvement Over the Entire Audio Band

“…The Class-D amplifier in this work uses a 14.4 V supply for the output stage and switches at 𝑓𝑓 𝑆𝑆𝑆𝑆 = 2.1 MHz to avoid interfering with the AM band and achieve high loop gain [11,13]. A fully differential 3 rd order loop filter based on active RC integrators is employed (Fig.…”

“…A fully differential 3 rd order loop filter based on active RC integrators is employed (Fig. 2) for high loop gain [13,25], with 𝑓𝑓 𝑈𝑈 = 570 kHz. The 1 st stage of A 1 is chopped to boost its CMRR and eliminate its 1/f noise.…”

A -109.1 dB/-98 dB THD/THD+N Chopper Class-D Amplifier with >83.7 dB PSRR Over the Entire Audio Band

“…The charge pump, shown in Fig. 4b, consists of 2 Schottky diodes (D1 and D2), an on-chip capacitor CCP, and reuses two off-chip bootstrap capacitors Cbst1 and Cbst2 that are already required in the floating gate driver circuits of the power transistors [5]. CCP is charged by Cbst1 and Cbst2 in an alternating fashion in each PWM cycle, holding VCP up to ~28 V. The level shifter is shown in Fig.…”

“…A PWM modulator driven by an on-chip oscillator runs at 2.1 MHz, which allows a relatively high loop gain for high linearity. A 3 rd order loop filter [5,7] is employed, which provides >80 dB loop gain within the audio band to suppress the distortion of the output power stage. The input stage of the 1 st integrator's OTA is sized such that its 1/f noise corner frequency is below fCHOP.…”

“…Alternatively, PSRR can be improved by removing feedback resistor mismatch using chopping. However, incorporating chopping into a pulse-width modulation (PWM) high-voltage (HV) CDA [2][3][4][5] is challenging. First, intermodulation between chopping and PWM in the audio band must be minimized.…”