Topic: Electronic Devices
An NPN transistor has a beta cut-off frequency $f_{\beta}$ of 1 MHz, and a common emitter short circuit low frequency current gain $\beta_{0}$ of 200, its unity gain frequency $f_{T}$ and the alpha cut-off frequency $f_{\alpha}$ respectively are
- A. 200 MHz, 201 MHz
- B. 200 MHz, 199 MHz
- C. 199 MHz, 200 MHz
- D. 201 MHz, 200 MHz
Answer: A. 200 MHz, 201 MHz
Explanation: $f_{T}=f_{\beta}\cdot\beta=(1\times200)MHz=200MHz$. $f_{\alpha}=\frac{f_{T}}{\alpha}=\frac{200}{0.99}=201MHz$ (since $\alpha = \beta/(1+\beta) = 200/201 \approx 0.995$).