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wideband VCO design using HBT

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zicothec

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Which configuration can be used for wideband VCO design?
common base ,common emitter or commn collector.
can you give me any example of calculs.

thanks
 

As the impedance of a tuned circuit is l/CR, sweeping a large frequency, means a wide variation of L or C, so the circuit impedance will vary a lot. Hence the need for high loop gain to ensure the oscillator actually oscillates right across the band. So I would go for common emitter. Though I fancy cross coupled FET oscillators because of the two terminal coil, earthed tuning capacitor and the loop gain of two transistors.
Frank
 
Thanks u frank , I read in many articles that the CB configuration can be the best one but really I don't see why.
U chose the CE , you have right that the common emitter provides the highest loop gain , but we don't need a highest one , only we need is a loop gain greater than one in order to have an oscillation.

zico
 

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