Question 7.SP.20: For the amplifier of Example 7.6, (a) use (7.9) to evaluate ......
For the amplifier of Example 7.6, (a) use (7.9) to evaluate the plate resistance and (b) use (7.10) to find the transconductance.
Plate resistance r_{p} \equiv {\frac{\partial v_{P}}{\partial i_{P}}}\Bigg|_{Q} \simeq {\frac{\Delta v_{P}}{\Delta i_{P}}}\Bigg|_{Q} (7.9)
Transconductance g_{m} \equiv {\frac{\partial i_{P}}{\partial v_{G}}}\bigg|_{Q} \simeq {\frac{\Delta i_{P}}{\Delta v_{G}}}\bigg|_{Q} (7.10)
(a) r_{p} \approx {\frac{\Delta v_{p}}{\Delta i_{p}}}\bigg|_{v_{G} = -4} = {\frac{218 – 152}{(14.7 – 8.1) \times 10^{-3}}} = 10\,\mathrm{k\Omega}
(b) g_{m} \approx {\frac{\Delta i_{P}}{\Delta v_{G}}}\bigg|_{v_{P} = 186} = {\frac{(14.7 – 8.1) \times 10^{-3}}{-2 – (-6)}} = 1.65\,{\mathrm{mS}}