The voltage gain for the given common source FET circuit is:
FET Parameters
- Yos = 10 ΞS
- Yfs = 3000 ΞS
Options
- A. -3
- B. -7.9
- C. 2.54
- D. -5
Solution
Given:
Yfs = gm = 3000 ΞS = 0.003 S
Yos = gds = 10 ΞS
Drain resistance of the FET:
ro = 1 / gds
ro = 1 / (10 × 10^-6)
ro = 100 kÎĐ
Given circuit resistances:
- RD = 2.7 kÎĐ
- RS = 2.7 kÎĐ
Since capacitor C2 bypasses RS, the source is AC grounded. Therefore the voltage gain for a common-source amplifier is:
Av = - gm (RD || ro)
Calculate parallel resistance:
RD || ro = (2.7k × 100k) / (2.7k + 100k)
≈ 2630 ÎĐ
Voltage gain:
Av = -0.003 × 2630
Av ≈ -7.9
Correct Answer: B. -7.9