Using FET as a varactor in 5GHz VCO.
时间：04-04
整理：3721RD
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Similarly to https://www.researchgate.net/publica...ESFET_varactor
, I am going to use FET as a varactor.
To test this idea I have added FET varactor to the cut near ground vias of quarterwave "finger" resonator. S21 maximum shifted from 5GHz to 9GHz (FET biased at Vgs=-1v). Simple analysis shows, that for simple quarterwave 5GHz resonator frequency will shift to 9GHz after adding 0.4pF series capactior. Does it mean that FET Cgs is around 0.4pF?
The only way to lower frequency back to 5GHz I see is to increase length of quarterwave resonator, which will become almost half-wavelength, is it reasonable?
, I am going to use FET as a varactor.
To test this idea I have added FET varactor to the cut near ground vias of quarterwave "finger" resonator. S21 maximum shifted from 5GHz to 9GHz (FET biased at Vgs=-1v). Simple analysis shows, that for simple quarterwave 5GHz resonator frequency will shift to 9GHz after adding 0.4pF series capactior. Does it mean that FET Cgs is around 0.4pF?
The only way to lower frequency back to 5GHz I see is to increase length of quarterwave resonator, which will become almost half-wavelength, is it reasonable?
Comparing the varactor capacitance with microstrip line impedance suggests that the varactor end is rather open than short circuit. Respectively the setup is nearer to halfwave resonance, you need to increase the line length for 5 GHz respectively. Halfwave is also the topology in the paper, I presume.