  Complimentary metal-oxide-semiconductor (CMOS) compatible quantum technology
enables scalable integration with the classical readout and control electronics
needed to build quantum computers. Homodyne detectors have applications across
quantum technologies including quantum computers, and they comprise photonics
and electronics. Here we report a quantum noise limited monolithic
electronic-photonic integrated homodyne detector, with an overall footprint of
$80~\mu\mathrm{m} \times 220~\mu\mathrm{m}$, fabricated in a 250~nm lithography
bi-polar CMOS process. By monolithic integration of the electronics and
photonics, overall capacitance is suppressed -- this is the main bottleneck to
high bandwidth measurement of quantum light. We measure a 3~dB bandwidth of
19.8~GHz and a maximum shot noise clearance of 15~dB. This exceeds bandwidth
limits of detectors with macroscopic electronic interconnects, including
wirebonding and flip-chip bonding. This demonstrates CMOS electronic-photonic
integration enhancing performance of quantum photonics.
