milk>試卷(2021/09/16)

110 年 - 110 國立臺灣大學_碩士班招生考試_電信工程研究所甲組:電子學(C)#101290

【非選題】
1.

1. The closed-loop circuit in Fig. 1 can be used as an oscillator. 【題組】(a) Please derive the condition to satisfy the Barkhausen criterion. What is the oscillation frequency? [10%]

【非選題】
2.【題組】

(b) Given that R = 10 kΩ, how do you choose RFand C to have an oscillation frequency of 100 kHz? [10%]

【非選題】
3.
2. For a MOSFET, the parameters are given as In Cox(W/L ) = 8 MA/V2, Vt= 1V and VA = 20 V. If the MOSFET is operated in saturation with a dc current of I, the transconductance is identical to that of a BJT operating in active mode with a dc current of 0.1I.

【題組】(a) Find the value ofI. [5%]

【非選題】
4.【題組】(b) What is the small-signal output resistance (ro) of the MOSFET? [5%]

【非選題】
5.【題組】(c) Find the intrinsic gain of the MOSFET. [5%]

【非選題】
6.【題組】(d) If the BUt has the same value of Vo, find the intrinsic gain of the BJT operating at a dc current of 0.1I. [5%]

【非選題】
7.

3. At higher frequencies, the MOSFET is characterized by its small-signal model by including  【題組】(a) The high-frequency current gain of the MOSFET is typically evaluated by the circuit in Fig. 3. Derive the transfer function of the current gain T(s) = Io/Is. [5%]

【非選題】
8.【題組】

(b) Based on T(s), find the unity-gain frequency ωt by assuming is relatively small. [5%]

【非選題】
9.【題組】

(c) For fixed DC voltage , how does ωt  change as channel width doubles? Why? [5%]

【非選題】
10.【題組】(d) For fixed DC voltage , how does  ωt  change as channel length doubles? Why? [5%]

【非選題】
11.

4. For the circuit in Fig. 4, assume the op-amp is ideal and the resistors are given as R = 5 kΩ, R1 = 10 kΩ, and R2 - 20 kΩ. 【題組】

(a) Given A for the diodes, find the output voltage when b,VI = 1 V. [5%]

【非選題】
12.【題組】(b) If the diodes are ideal, plot the voltage transfer curve (plot of Vo versus VI). Find the output voltage when  V= 1 V. [10%]

【非選題】
13.

5. Assume C1 and C2 are ideal coupling capacitors for the circuits in Fig. 5.  【題組】

(a) For the circuit in Fig. 5(a), find the input resistance , output resistance (RO) and open-circuit voltage gain of the amplifier. [15%]

【非選題】
14.【題組】(b) For the circuit in Fig. 5(b), find the bias current I needed to obtain a voltage gain (vo/vs) of 15. [10%]

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