## Analogue Electronices;

Analogue Electronices;

APPROVED

___________________________________________________________________________________

EXAMINATION PAPER: ACADEMIC SESSION 2011/2012

Campus

Medway

School

Engineering

Department

Engineering Systems

Programme

BEng Engineering Suite

COURSE TITLE

Analogue Electronics

COURSE CODE

ELEE0052

LEVEL

Two

Date and Duration

(incl. reading time)

May 2012, 2 Hours

Paper Set By

Dr R Wu

INSTRUCTIONS TO CANDIDATES

&

INFORMATION FOR INVIGILATORS

The attention of the students is directed to the instructions printed on the

answer book.

Answer THREE of the following four questions.

All questions carry equal marks.

———-

___________________________________________________________________________________

Date & Duration of Exam:

May 2012, 2 Hours

Course Title:

Course Code:

Analogue Electronics

ELEE0052

Page 1 of 7

APPROVED

___________________________________________________________________________________

Q1.

(a)

If a BJT transistor is operating in the active mode, what is the DC

biasing requirement for the PN junctions?

[4 marks]

(b)

An amplifier circuit is shown in Figure Q1(b).

(i)

What is the role of the resistor RE? Why?

[5 marks]

(ii)

Discuss the role of the capacitor CE in terms of voltage gain.

[5 marks]

+VCC

R1

RS

RC

CC2

CC1

CE

vS

R2

RL

vo

RE

Figure Q1(b)

(c)

In the RC filter shown in Figure Q1(c)(i) (see page 3): R2=R4=1k?,

RL=4.7k?, C1=1µF, C3=0.1µF. The Op-Amp is 741 type. The OpAmp can be modeled as a voltage-controlled voltage source, as shown

in Figure Q1(c)(ii) (see page 3). Ri and Ro are the input and output

resistances, respectively. Ao is the open-loop DC voltage gain. For

µA741 Op-Amps, Ri=2M?, Ro=75?, Ao=2 × 105.

If the input to the filter is a 100mV AC voltage source whose frequency

will be varied between 1Hz and 1MHz logarithmically with

100 points-per-decade, write the PSPICE input file to calculate the

frequency response of this filter. (In the Op-Amp model, a DC voltage

source with V=0 can be connected between node 1 and the ground to

simulate the grounded non-inverting terminal).

[11 marks]

Cont’d…..

___________________________________________________________________________________

Date & Duration of Exam:

May 2012, 2 Hours

Course Title:

Course Code:

Analogue Electronics

ELEE0052

Page 2 of 7

APPROVED

___________________________________________________________________________________

Question 1(c) Continued.

C3

C1

R4

R2

vi

RL

vo

Figure Q1(c)(i)

5

2

vd

Ri

Ro

3

Aovd

vo

0

1

Figure Q1(c)(ii)

___________________________________________________________________________________

Date & Duration of Exam:

May 2012, 2 Hours

Course Title:

Course Code:

Analogue Electronics

ELEE0052

Page 3 of 7

APPROVED

___________________________________________________________________________________

Q2.

(a)

Figure Q2(a) shows a differential amplifier fed by a common-mode

voltage signal vCM. If the output is taken single ended, assuming

R>>rbe, ß/(ß+1)˜1, derive the voltage gain vc1/vCM or vc2/vCM by using

the concept of the common-mode half-circuit.

[10 marks]

VCC

RC

RC

vc 1

vc2

Q1

v

Q2

v

CM

R

CM

I

-VEE

Figure Q2(a)

(b)

In the differential amplifier shown in Figure Q2(b) (see page 5),

RC=5.1k?, R=100k?, I=1mA, ß=145.

(i)

What is the requirement for Q1 and Q2 in semiconductor device

manufacturing? What is the role of the current source I?

[5 marks]

(ii)

Determine the input differential resistance Rid.

[4 marks]

(iii)

Determine the differential-mode gain Ad.

[3 marks]

(iv)

Determine the common-mode rejection ratio (CMRR) in dB.

[3 marks]

Cont’d…..

___________________________________________________________________________________

Date & Duration of Exam:

May 2012, 2 Hours

Course Title:

Course Code:

Analogue Electronics

ELEE0052

Page 4 of 7

APPROVED

___________________________________________________________________________________

Question 2(b) Continued.

VCC +5V

RC

RC

Vo

Q1

Q2

Vi

R

I

VEE -5V

Figure Q2(b)

___________________________________________________________________________________

Date & Duration of Exam:

May 2012, 2 Hours

Course Title:

Course Code:

Analogue Electronics

ELEE0052

Page 5 of 7

APPROVED

___________________________________________________________________________________

Q3.

(a)

How to determine the type of feedback in terms of the gain of a

system?

[3 marks]

(b)

In the common-emitter amplifier shown in Figure Q3(b): Rs=4k?,

R1=10k?, R2=5k?, RE=1k?, RC=2k?, RL=5k?, VCC=12V. The

transistor parameters are: ß=100, Cp=10pF, Cµ=2pF.

(i)

In this amplifier, the gain falloff in the high frequency band is

due to the effects of which capacitors?

[3 marks]

(ii)

Find its DC equivalent circuit, and hence determine IC, VB,

VC and VE.

[7 marks]

(iii)

Find the small signal equivalent circuit (gm, rp) for the

transistor, and hence determine the midband gain.

[5 marks]

(iv)

Find its high-frequency equivalent circuit. Use the miller-effect

method to determine the total input capacitance and hence the

upper 3-dB frequency fH (the dominant high-frequency).

[7 marks]

+VCC

R1

Rs

CC2

RC

CC1

CE

Vs

R2

RL

RE

Figure Q3(b)

___________________________________________________________________________________

Date & Duration of Exam:

May 2012, 2 Hours

Course Title:

Course Code:

Analogue Electronics

ELEE0052

Page 6 of 7

APPROVED

___________________________________________________________________________________

Q4.

(a)

An amplifier shown in Figure Q4(a) is intended to supply a voltage to

floating loads (those for which both terminals are ungrounded) while

making greatest possible use of the available power supply. Assuming

that ideal Op-Amps are used;

(i)

Determine its voltage gain: vo/vi.

[10marks]

If R1=10k?, R2=5k?, R3=15k?, what is the voltage gain?

Sketch the output voltage waveform vo for a 1V peak-to-peak

sine wave applied at A.

[8 marks]

(ii)

R2

R1

B

R1

A

v?

R3

R1

v?

R1

C

Figure Q4(a)

(b)

For the Wien-bridge oscillator shown in Figure Q4(b).

(i)

If C=0.01µF, what is the value of R to generate an oscillation

frequency of fo=10kHz?

[4 marks]

(ii)

If R2=10k?, determine the value for R1.

[3 marks]

R2

R1

Vo

R

Vi

R

C

C

Figure Q4(b)

___________________________________________________________________________________

Date & Duration of Exam:

May 2012, 2 Hours

Course Title:

Course Code:

Analogue Electronics

ELEE0052

Page 7 of 7

PLACE THIS ORDER OR A SIMILAR ORDER WITH US TODAY AND GET AN AMAZING DISCOUNT 🙂