Adaptive and Robust Digital Harmonic-Reject Mixer With Optimized Local Oscillator Spacing

Harmonic-reject mixers (HRM) are commonly used in wideband receivers to suppress the effects of spurious harmonic interferers. Both analog and digital HRMs have been proposed in the literature. In existing works, the local oscillator (LO) phases are assumed to be equally spaced. When viewed as a multiuser access system, the drawback of equally-spaced LO phases is that the signature vectors of the desired signal and some harmonic interferers become aligned, limiting the number of interferers that can be attenuated. In this paper, a digital HRM with non-uniform phase spacing that can suppress additional harmonics while being robust to gain and phase mismatches is described. This paper also presents a low-complexity, adaptive and robust digital HRM receiver that enables the fewest LOs and analog-to-digital converters necessary depending on the interference environment for low power. The performance of the adaptive non-uniformly spaced HRM is shown to be significantly superior to existing HRMs with equal LO phase spacing.