This paper presents a Class-D audio amplifier, fully compatible with standard BCD technologies, that features in the direct signal path an ADC ($\Sigma\Delta$ modulator), a digital third-order loop-filter and digital PWM. The overall closed-loop mixed-signal architecture pushes most of the signal processing towards the digital domain, thus allowing the use of scaled technologies to reduce cost and size. Moreover, the high gain developed by the digital filter and by the integrator inside the $\Sigma\Delta$ modulator, attenuates the residual high frequency ripple around the loop and concurrently improves the THD+N in the audio band. In this paper the feedback is closed after the output LC filter, thus mitigating the influence of its components on the amplifier transfer function and on the linearity. The proposed architecture achieves in simulation 120 dB of SNR and a THD of 0.01\%-0.001\%, even in wide input signal conditions.