A CMOS-Compatible Spectrum Analyzer for Cognitive Radio Exploiting Crosscorrelation to Improve Linearity and Noise Performance

A spectrum analyzer requires a high linearity to handle strong signals, and at the same time a low NF to enable detection of much weaker signals. This is not only important for lab equipment, but also for the spectrum sensing part of cognitive radio, where low cost and integration is at a premium. Often there is a trade-off between linearity and noise: improving one degrades the other. Crosscorrelation can break this trade-off by reducing noise at the expense of measurement time. An existing RF frontend in CMOS-technology with
${{\rm IIP3}}\!=\!{+}11$
dBm and
${\rm NF}\!=\!5.5$
 dB is duplicated and attenuators are put in front to increase linearity to
${\rm IIP3}={+}24$
dBm. The attenuation degrades NF, but by using crosscorrelation of the outputs of the two frontends, the effective NF is reduced to around 5 dB. In total, this results in a spurious-free dynamic range of 88 dB in 1 MHz resolution bandwidth.