  In this work we explore monolithic opto-electronic integration platform for
significant down-scaling of input-referred noise in custom designed low-noise
analog front-end used for balanced photodetection. The performance of such
monolithically integrated approach is compared to heterogeneously integrated
solution designed in the same technology which requires wire-bonding to the
balanced photodetectors. The designed circuits are targeting bandwidth above 1
GHz. The improved noise performance is leveraged against increased secure key
rates and achievable reach in continuous-variable quantum key distribution
(CV-QKD).
