EE251 Lectures
Application Specific Circuits
Section 06
Contents
• Generators
– Square Wave Generator / Sine Wave Generator – Pulse Generators
• AC/DC Converters
• Protection Circuits
– Voltage/Current Limiter – Reverse Polarity
– ESD Protection
• Math Circuits
– General adders
– Integrators, Differentiator
• Analog-Digital Converters
• Filters
– Low/High Pass Filters
– Band Pass/Stop Filters
Electrical & Computer
Engineering King Abdulaziz University
Slide 3
Format
1. Circuits Schematic
2. Function
3. Usage
4. Design Equations
5. Design Example
Note!!
• Some are Conceptual Designs
• Consider Ready-Made IC’s available
• Or even PCBs
Electrical & Computer
Engineering King Abdulaziz University
Slide 5
Op-Amp
• Needs Dual Power Supply
• Multiple op-amps in one IC
Square Wave Generator
f RC
2 . 2
≈ 1
Electrical & Computer
Engineering King Abdulaziz University
Slide 7
Pulse Generator
( )
C R
t
C R
R t
×
×
=
× +
×
=
2 2
2 1
1
2 ln
2
ln
AC/DC Converter
optional
D ac
dc V
n v n
v = − 2 ⋅
1 2
load dc R C f r v
⋅
⋅
≈ ⋅
2
Electrical & Computer
Engineering King Abdulaziz University
Slide 9
Example
• design an AC/DC converter to:
– Produce 8.4 VDC – Ripples 1%
– Diodes available V D =0.6V
– Maximum load expected 2kΩ
D ac
dc V
n v n
v = − 2 ⋅
1 2
load dc R C f
r v
⋅
⋅
≈ ⋅
2
Clipping Protection
+
−
− +
+
=
+
=
f z
l
f z
u
v v
V
v v
V
Electrical & Computer
Engineering King Abdulaziz University
Slide 11
ESD Protection
• Simple Parallel Discharging Zener Diode
• Special Diodes for High speed Lines
Reverse Polarity Protection
optional L
L R B
I ≈ v
Electrical & Computer
Engineering King Abdulaziz University
Slide 13
General Adder (Mixer)
∑
∑ = =
−
= m
i
ni i
n
i
pi i
o A v B v
V
1 1
ni f i
pi f
i
R
B R R
A = R , =
1 ,
, = = − −
= ∑ A B ∑ B C A B
A
Let
i i
∞
=
−
=
<
=
∞
=
≥
y f
x
f y
x
C R R R
C
C R R
R C
0
0
Integrator
>
−
≤
−
= ∫ 0
0
)
1 v ( t dt f f C
R
f R f
R v
s S
o S
f RC
= π 2
0 1
Electrical & Computer
Engineering King Abdulaziz University
Slide 15
Differentiator
>
−
≤
= −
0
) 0
(
f r f
R
f f
t dt v
RC d
v o s
f rC
= π 2
0 1
Filters
Electrical & Computer
Engineering King Abdulaziz University
Slide 17
Filter Shape
Designing a Filter
1. Select the shape
2. Set cut-frequency f0 3. Select Filter Order
4. Generate Filter Poles Using Filter Equations
5. Implement Poles
Electrical & Computer
Engineering King Abdulaziz University
Slide 19
Example
• Butterworth Low Pass Filter
– Specs:
• A max = 1 dB
• A min = 25 dB
• f p = 10 kHz
• f s = 15 kHz
Solution
9 17 , 2
9 15 , 2
9 13 , 2
9 11 , 2
, 2 9 7 , 2 9 5 , 2 9 3 , 2 9 1 2
730 ,
5088 67 .
0 000 1
, 10 2
5088 .
0 1
10
9 7609
. 8 000
, 10 2
000 ,
15 log 2
1 10
1 log 10
9 1
0
10 1 10
10 1 10 25
10
π π
π π
π π
π π
θ π
π ω
ε
π π
=
=
×
⋅
=
=
−
=
→
=
⋅
⋅
−
−
≥
k
n
Electrical & Computer
Engineering King Abdulaziz University
Slide 21
Solution
730 ,
67
165 ,
23 645
, 63
536 ,
43 884
, 51
656 ,
58 865
, 33
701 ,
66 761
, 11
−
±
−
±
−
±
−
±
−
=
j
j
j
j
p k
The Design
Expect:
Errors in Specs due to Resistors Tolerances!!
Electrical & Computer
Engineering King Abdulaziz University
Slide 23
Process Check
• What circuits did you face in your field?
• Do you need more details?
• Where to find more Designs?
