Dynamic spectrum access relying on spectrum sensing requires reliable detection of signals in negative signal-to-noise ratio (SNR) conditions to prevent harmful interference to licensed users. Energy detection (ED) is a quite general solution, which does not require any knowledge of the signals to be detected. Unfortunately, it suffers from noise uncertainty in the receiver, which results in an SNR-wall below which signals cannot be reliably detected. Furthermore, distortion components originating from nonlinearity in the sensing receiver cannot be distinguished from true input signals, and is thus another effect that may obscure weak signals and cause false alarms or missed detections. Cross-correlation was recently proposed to reduce the SNR-wall and, at the same time, allow the receiver to be designed for high linearity. This allows for high-fidelity spectrum sensing, both in the presence of strong interference as well as for signals with a negative SNR. In this work, an integrated complementary metal-oxide-semiconductor prototype exploiting cross correlation is presented and tested in practice. The prototype achieves a high linearity of +25 dBm IIP3 at a sensitivity of -184 dBm/Hz, 10 dB below the kT noise floor. The measured results agree well with theory, and, compared to the traditional ED-approach, show both a significant improvement in sensing time, as well as a reduction of 12 dB in the SNR-wall itself. Overall, cross-correlation makes ED faster, more sensitive, more resilient to strong interferers, and more energy-efficient.