Electrical Engineering Answers

f(x,y)=cxy,for x=1,2,3;y=1,2,3

a) Find multiplier values 𝑛1 and 𝑛2 in a indirect WBFM generator (the Armstrong method)

using two step multiplier where the message signal 𝑚(𝑡) has bandwidth 500 Hz and

narrowband modulator has a modulation index 0.2 and carrier frequency 120 KHz.

The output frequency is to be 120 MHz with the modulation index of 720.

b) The output WBFM signal in (a) can also be generated by a variant of the Armstrong

method, as shown below, where carrier frequency of 𝑣3(𝑡) is lowered by amount of 𝜔2.

In other words, two multipliers are separated by mixer. Find multiplier values 𝑚1 and 𝑚2

with 𝜔1 = 100 𝑘𝐻𝑧 and 𝜔2 = 4 𝑀𝐻𝑧 .(Note: Here two BPFs that follow the frequency

multiplier are not shown)

c) Comment your results. Which generator is more practical? Justify your conclusion.

(3) The transfer characteristic of MOS transistor is the dependence of ( ). 

A. Drain voltage on gate-source voltage B. Drain voltage on drain-source voltage

C. Drain current on drain-source voltage D. Drain current on gate-source voltage

(4)The drain of an n-channel MOSFET is shorted to the gate so that VGS = VDS. The 

threshold voltage (VT) of the MOSFET is 1 V. If the drain current (ID) is 1 mA for 

VGS = 2 V, then for VGS = 3 V, ID is ( ). 

A. 2 mA B. 3 mA C. 9 mA

(1) An NMOS transistor starts to conduct when the potential difference between

( ) is higher than the threshold voltage VT.

A. the drain and the source terminals B. the gate and the source terminals

C. the gate and the drain terminals D. the drain and the base terminals

(2) Which of the following is NOT true? ( ).

A. QOX is a function of applied gate voltage.

B. Threshold voltage is a function of tox.

C. P+ Poly silicon gate is usually used for n-MOS capacitor.

D. Once the strong inversion occurs, Qd (=the depletion charge) is approximately

unchanged with VGS.

Consider an n+-poly-Si-gated n-MOSFET with substrate dopant concentration NA = 

1016 cm-3, gate-oxide thickness tox = 0.12 μm, and Qox/q = 9 × 1010 cm-2. Calculate 

the threshold voltage, VT, of the MOS transistor.

Consider an n-channel MOSFET with W = 15 μm, L = 2 μm, and COX = 6.9×10-8

F/cm2. Assume that the drain current in the linear region for VDS = 0.10 V is IDS = 35 

μA at VGS = 1.5 V and IDS = 75 μA at VGS = 2.5 V. Determine the inversion carrier 

mobility and the threshold voltage from experimental results.

Consider an n+-poly-Si-gated long-channel n-MOSFET with W/L = 10, effective 

gate-oxide thickness Toxe = 2 nm, and substrate (body) dopant concentration NA = 

1018 cm-3. εSi02 = 3.9, εSi = 11.9. 

(1) Calculate the body effect parameter, γ. 

(2) How can the body effect be minimized?