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  1. It is desired to design a phase shift oscillator using an FET having a gm = 5000 μSiemen, rd = 40 kΩ and feedback circuit value of R = 10 K. Then value of C for oscillator operation at 1 kHz and that of RD for A = 40 to ensure oscillator action are

    2. A.
    6.4 nF, 80 K
    B.
    6.5 nF, 10 K
    C.
    6.5 pF, 10 K
    D.
    65 pF, 80 K

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    Answer : Option B

    Explanation :

    For a FET oscillator, the oscillator frequency is

    ∴

    C = 6.4 nF

    For FET Oscillator,

    |A| = gmRL = 5000 x 10-6 RL

    i.e., 40 = 5000 x 10-6 x RL

    ∴ = 8 KΩ

    Now,

    Using RL = 8 K and rd = 40 K (given)

    We find RD as follows:

    ∴

    ∴ = 10 K

    RD = 10 K.

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