Cover Sheet Quiz #4 STC frequency domain analysis
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Transistor topologies:
1. General Purpose topology 2. Voltage follower
3. Current follower g m

40 I for BJT g m

2

I for jFET g m

2 KI for MOSFET K

1
2

0
C
OX
W
L
Single-time constant analysis:
Low freq corner: p
L
 p
L 1
 p
L 2
 p
L 3
  
Parasitic (high freq) capacitances:
C


C
JC
1
High freq corner: p
H
C


C
JE
 g m
 
Miller
C
GD
(capacitance multiplication)

C
GDO

W
effect: C
'
12

C
Cs
12

2


 1
3

C
OX v v
2
1



W

L

1 p
H 1

1 p
H 2

1 p
H 3
  
- for BJT
- for MOSFET

ECE3424 Quiz #4: STC analysis and frequency response 24 Apr 2009
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Instrux: Show work in space provided Be neat, concise, encircle answers Else –10 pts
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Defaults:

F
= 100, Resistances in k

, T = 300K, 4 kT = 1.6 x 10 -20 J
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Figure Q1: CE configuration
C-1. (14 pts) The above circuit is identical to the pSPICE homework part I except that source resistance R
S
=
60k instead of 120k. Determine the RC time constants (ms) and the low frequency poles (kr/s) for the capacitances C
1
, C
2
, and C
3
. In each case identify the resistance value used with the capacitance. Identify which pole is dominant by means of an *
(a)

1
= _____________ p
L1
__________
(b)

2
= _____________
(c)

3
= _____________ p
L2
__________ p
L3
__________
C-2 (14 pts) Figure Q1: Assume that C
JC
= 3.6pF and C
JE
= 4.5pF. Determine the values of:
(a) C 

(b) C 
’
(due to Miller effect)

(c) p
H1
associated with node N1 (base node)


Figure Q2: BJT Cascode configuration
C-3. (14 pts) The above circuit is identical to the pSPICE homework part II except that the source resistance
R
S
= 100k instead of 25k. Determine RC time constants (ms) and the low frequency poles (kr/s) for capacitances C
1
, C
2
, and C
3
.. Identify which pole is dominant by means of an *
(a)

1
= _____________
(b)

2
= _____________ p
L1
__________ p
L2
__________
(c)

3
= _____________ p
L3
__________
C-4. (14pts) Figure Q2. Assume that C
JC
= 3.6pF and C
JE
= 4.5pF. Determine the high frequency RC time constants (ns) and poles in Mr/s and identify which pole is dominant by means of an *
(a)


1
= _____________ p
H1
__________
(b)

H2
= _____________
(c)

H3
= _____________ p
H2
__________ p
H3
__________
C-5 (5pts) What is the gain-bandwidth product for figure Q2? GB = ________________

C-6 For the T54J MOSIS parameters shown (cover sheet 2) and the circuit of figure M-1 determine:
(a) the values of K and g m
(6 pts)
K = _____________ g m
= _____________
(Note : W/L = 12
 m/0.6
 m)
(b) the values of the parasitic capacitances (6pts)
(a)
(b)
C
C
GS
GD
= _________________
= ________________
Figure M-1: MOSFET CS configuration
(c) The values of the low frequency time constants and poles (14pts). Identify which pole is dominant.
(a)

1
= _____________ p
L1
__________
(b)

2
= _____________
(c)

3
= _____________ p
L2
__________ p
L3
__________
(d) (10pts) Figure M-1. Determine the high frequency the RC time constants and poles in Mr/s and identify which pole is dominant by means of an *
(a)


1
= _____________ p
H1
__________
(b)

H2
= _____________ p
H2
__________
(e) (5pts) What is the gain-bandwidth product for figure Q2? GB = ________________

B-1 (18pts) For the circuit topology of figure M1 identify the effect on the frequency characteristics of the circuit by means of an (X)
Double the value of R
L
(Decrease) (~No change) (Increase)
(a)
(b)
(a) f f
L
H
GB
( )
( )
( )
( )
( )
( )
( )
( )
( )
Double the value of Ix
(a) f
L
(b) f
H
(a) GB
( )
( )
( )
Double the size of W (width of the transistor)
(a) f
L
(b) f
H
( )
( )
(a) GB ( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
A-1: Bonus questions (Miscellaneous)
(a) (3 pts) What is the value of the (naperian) e to 50 decimal places?
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(b) (3 pts) What is the value of 1 2 to 50 decimal places?
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(c) (4 pts) The earth (1.0AU) is 500sec from the sun (by light speed). Venus is 0.72AU from the sun and
Mars is 1.52AU from the sun. If Sam is visiting Mars and Susie is visiting Venus, what is the minimum time for which Sam can expect a reply to an email to Susie if they are in planetary quadrature (and she is not mad at him)?
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