  We present the design and the performance of MUX64, a 64-to-1 analogue
multiplexer ASIC for the ATLAS High Granularity Timing Detector (HGTD). The
MUX64 transmits one of its 64 inputs selected by six address lines for the
voltages or temperatures being monitored to an lpGBT ADC channel. The prototype
ASICs fabricated in TSMC 130 nm CMOS technology were prepared in wire-bonding
and QFN88 packaging format. A total of 280 chips was examined for functionality
and quality assurance. The accelerated aging test conducted at 85 degrees
celsius shows negligible degradation over 16 days.
