Effect of Out-of-Band Blockers on the Required Linearity, Phase Noise, and Harmonic Rejection of SDR Receivers Without Input SAW Filter

Abstract

The required linearity of wideband receivers for applications, such as software-defined radio in the absence of input surface-acoustic wave (SAW) filters, is studied. It is shown that the required linearity of wideband SAW-less receivers is surprisingly higher than what has been commonly assumed. For these receivers, although the out-of-band blockers can reduce the compression point of the receiver, they can also potentially generate interferers that appear in the desired frequency band, resulting in higher noise floor and signal corruption. The required out-of-band IIP2 and IIP3 of low-noise amplifier (LNA) and mixer for single and concurrent applications are analytically derived. The required wideband SAW-less receiver phase noise is also studied, and it is shown that blockers located at the frequencies of the local oscillator harmonics can significantly increase the noise floor of the receiver. The effects of input and intermediate filters on the above applications along with the conditions under which they help to alleviate the limitations of LNA and mixer are defined. The validity of the models and subsequent derivations is verified by actual measurements using a wideband SAW-less receiver.