Due 2pm Monday 31st August 2015

Department of Electronic Engineering

La Trobe University

ELE2ANI – Analog Circuits & Interfacing

Assignment 2

Name: …….....................................……… Student Number: ……….................................

Subject: ELE2ANI Lecturer: Adam Console

Assignment: 2

DECLARATION: I certify that the above assignment is my original work and that no part of it has been

copied or reproduced from any other person’s work without acknowledgement.

Signed: …………………………………… Date: …………………………………………

1. In the amplifier circuit below all transistors have β = 100 and VBE(ON) = 0.7V. Q1 and Q2 have

r0 ∞ and Q3 and Q4 have |VA| = 200V.

(a) Describe the function of the transistors Q3 and Q4 and calculate the value of R required to ensure

the circuit supplies the 2mA emitter biasing current.

[3 marks]

I REF

Q3 Q4

R

Q1 Q2

a

v o + _

I = 2mA EE

1k 1k

5k 5k

v v 1 2

V = 15V CC

Rout

(b) Using the Hybrid- model in the small-signal circuit, calculate the small-signal output resistance

outR seen from the junction “a” connecting the emitter circuits of Q1 and Q2.

[3 marks]

(c) Use the Hybrid- model to draw the small signal equivalent half-circuits for both the differential

mode and common-mode inputs.

[4 marks]

1. 2. For the NMOS transistors in the circuit below, all transistors have 2'n V/mA2k , Vt = 0.7V,

W = 9µm, L = 2 µm and Q3 and Q4 have r0 ∞ and Q1 and Q2 have |VA| = 100V.

(a) What is the function of Q1 and Q2? Determine the value of R required to give a drain current in

Q2 of 1mA.

[3 marks]

1mA

I REF

V GS

+

_

Q1 Q2

R Q3 Q4

2k 2k

I D1

v o

+ _

v i1 v i2

V = 10V DD

Rout

a

(b) Using the Hybrid- model in the small-signal circuit, calculate the small-signal output resistance

outR seen from the junction “a” connecting the source circuits of Q3 and Q4.

[3 marks]

(c) Use the Hybrid- model to draw the small signal equivalent half-circuits for both the differential

mode and common-mode inputs.

[4 marks]

3. For the amplifier circuit below:

Assume VBE = 0.7V, β = 100, |VA| = 200V and VT = 25mV.

(a) Name the type of amplifier configuration.

[1 mark] (b) Find the Thevenin equivalent circuit of the base-biasing circuit and then calculate the DC currents

IB, IC and IE and the DC voltages VE, VB and VC.

[3 marks]

v sig + _

10V

v C

C

C

C1

C2

E

o

43k

2.4k

6.2k

4.3k

4.3k

10V

75k

i i

750

i o

Ri

Ro

RL Rsig

(c) Draw the AC equivalent circuit.

[2 marks]

(d) Use the T-model to draw the small signal equivalent circuit.

[3 marks]

(e) Calculate the input resistance Ri.

[1 mark]

(f) Ignoring r0 calculate Av the voltage gain from base to collector. (including RL)

[2 marks] (g) Again ignoring r0 calculate Gv, the overall voltage gain.

[4 marks]

(h) Calculate Ai, the overall current gain.

[4 marks]

4. For the amplifier circuit below:

+ 12V

7.5k

2k

10k

vovgs

3M

6M

+

_sig

v

100k

Rin

(a) Name the type of amplifier configuration.

[1 mark]

(b) If Vt = 1.8388V and 2'n V/mA2

L

Wk

, verify that the bias circuit establishes VGS = 2.658V, ID

=0.671mA and VD ≈ +6.97V.

(c) Find the Thevenin equivalent circuit of the gate-biasing circuit and then calculate the DC currents

IG, ID and IS and the DC voltages VS, VG and VD.

[3 marks]

(d) Draw the AC equivalent circuit.

[2 marks]

(e) Use the T-model to draw the small signal equivalent circuit. (VA = 200V)

[3 marks]

(f) Calculate the input resistance Ri.

[1 mark]

(g) Including r0 calculate Av the voltage gain from base to collector. (including RL)

[2 marks]

(h) Again including r0 calculate Gv, the overall voltage gain.

[4 marks] (i) Calculate Ai, the overall current gain.

[4 marks]