Question

For the circuit below lambda is about 0, k is 32 mA/V^2.

1. Find a value for Rs1 so that Id=1mA, if voltage threshold, Vt= 0.75V. Is the FET in the active operating region?
2. Assuming that Id= 1mA as in part 1, estimate the midband voltage gain. (Capacitors are replaced with short circuits)
3. If Rs1 is the same as you found in part 1 and k = 32 mA/V^2, BUT Vt=0.65V, estimate Id.
4. Repeat part 2 if C3 is removed.
5. Repeat part 2 if lambda is about 0.1 V^-1.

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Answer 1

DC analysis (open ckt all capacitors) V_G = 60/150 times 6 = 12/5 = 2 . 4 v Let assume Fet is in saturation I_0 = 1/2 k n (V_Gs - V_E)^2 I_0 = 1/2 k n (V_G - I_0 R_G - V_t)^2 1 = 32/2 (2 . 4 - R - 0 . 75)^2 1/16 = (1 . 65 - R)^2 = 2 . 7225 + R^2 - 3 . 3 R R^2 - 3 . 3 R + 2 . 66 = 0 R = 3 . 3/2 plusminus 0 . 25 R = 1 . 9 k, 1 . 4 k V_Gs > V_t