  Synthesis models of the diffuse Cosmic X-ray Background (CXB) suggest that it
can be resolved into discrete sources, primarily Active Galactic Nuclei (AGNs).
Measuring the CXB accurately offers a unique probe to study the AGN population
in the nearby Universe. Current hard X-ray instruments suffer from the
time-dependent background and cross-calibration issues. As a result, their
measurements of the CXB normalization have an uncertainty of the order of
$\sim$15%. In this paper, we present the concept and simulated performances of
a CXB detector, which could be operated on different platforms. With a 16-U
CubeSat mission running for more than two years in space, such a detector could
measure the CXB normalization with $\sim$1% uncertainty.
