Avalanche photodetectors (APDs) integrated in a silicon platform have the potential to significantly improve the link budget of optical links compared with conventional p-i-n photodetectors, while only requiring CMOS-friendly biasing voltages. We demonstrate an optical receiver based on a 1310nm <5V Germanium APD and a low-power transimpedance amplifier that offers a 5 to 6 dB sensitivity improvement compared with operation in PIN-mode. Sub-FEC transmission using PAM-4 in an amplifier-less link over more than 42km at 40Gb/s and over 10 km at 50 Gb/s is shown with a commercial directly modulated laser as transmitter.