Analysis of Specially Doped Varactors for Direct Frequency Tripling

Specially doped (N = N0/√x) varactors offer a cubic relation between voltage and charge. Frequency tripling is thus possible without an idler frequency excitation at twice the input frequency. Here we have investigated a frequency tripler from 2.115 to 6.345 GHz without an idler frequency at 4.23 GHz, thus hopefully reducing the cost and complexity of the tripler. The results from such varactors indicate that, although frequency tripling is possible over a wide band, the efficiency and power-handling capacity are considerably lower than conventional frequency tripling with abrupt junction varactors excited at 4.23 GHz. The impedance matching is harder for these specially doped varactors, even though the mechanical construction is greatly simplified.