Revised Scope: Design and Implementation of a Portable Bus-Powered Dual-Mono USB-C DAC/AMP on the XMOS XU208 Platform

Abstract

This thesis documents the design and implementation of a portable, bus-powered USB-C digital-to-analog converter and headphone amplifier (DAC/AMP) on a 4-layer mixed-signal PCB. A review of the commercial portable DAC/AMP market shows that budget and mid-range devices typically rely on single-stereo DAC architectures, PLL-derived clocks and limited power distribution, while XMOS XU208-based designs have so far been restricted to desktop devices.

The design evolved through two architectures and three revisions. Version 1, a desktop architecture, produced simulation work including a MOSFET-based capacitance multiplier achieving -112.12 dB power-rail SNR. Version 2 initially used the CT7601CR MCU, which was replaced by the open-source XMOS XU208 USB audio processor due to its closed firmware ecosystem. The final design implements a true dual-mono architecture with two independent CS43131 DAC/AMP chips, three independent crystal oscillators for jitter-free master clock distribution, and a cascaded power distribution network (TPS7A9101, LT3045 and SGM2036 regulators) that isolates the analog supply chain from USB VBUS noise. It provides both 3.5 mm single-ended and 4.4 mm balanced outputs within the USB 2.0 500 mA current budget.

Design decisions were based on manufacturer design guides, datasheets and established EMC literature, and a failure mode and effects analysis (FMEA) was performed on the final revision. The fabricated board is ready for assembly, and a three-phase verification methodology (power-on, firmware bring-up and audio performance measurement) is defined to validate the theoretical performance in hardware.