An accumulation-mode MOS varactor is formed with a standard CMOS process and having an anti-symmetric-CV curve. The asymmetric varactor (ASVAR) can efficiently generate even-order harmonics while simultaneously suppressing odd-order harmonics over broad bandwidths. This is achieved without degradation of dynamic cut-off frequency. The improved cut-off frequency of the asymmetric varactor results in efficient even-harmonic generation well into sub-millimeter or terahertz frequencies. This and the inherent adaptive-CV features of the asymmetric varactor result in even-harmonic generation with process variation resilience and can also be utilized for frequency response shaping and for optimizing performance at various driving conditions.