Using Crosscorrelation to Mitigate Analog/RF Impairments for Integrated Spectrum Analyzers

An integrated spectrum analyzer is useful for built-in self-test purposes, software-defined radios, or dynamic spectrum access in cognitive radio. The analog/RF performance is impaired by a number of factors, including thermal noise, phase noise, and nonlinearity. In this paper, we present an integrated circuit with two integrated RF-frontends, of which the outputs are crosscorrelated in digital baseband. We show by theory and measurements that the above-mentioned impairments are mitigated by this technique. The presented 65-nm CMOS prototype operates at 1.2 V, and obtains a noise floor below -169 dBm/Hz, an IIP₃ of +25 dBm, and more than 20 dB of phase-noise reduction. In a special high-impedance mode, an even lower noise floor below -172 dBm/Hz is obtained.