Ch(1) Signal Processing Circuits
WAVESHAPING CIRCUITS
Major virtue of electronic circuits F the ease of z
Controlled F Voltage Û current waveforms
Some of the basic waveshaping functions z
radar pulse – train generator
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Ch(1) Signal Processing Circuits
Clipping ‫ﺗﺸﺬﻳﺐ‬
Removing F undesired portion of a signal
The waveshape function performed by the circuit
components arranging
Consisting F diode Û resistance Û voltage source
Input signal F V1 F varies with time
Output signal F VD Û VR
The sum of the voltage around the loop = zero
vD + vR = v1 – V
vR = v1 – V - vD
vD = v1 – V - vR
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Ch(1) Signal Processing Circuits
The behavior of the circuit F depends on the
state of the diode F switch F (S)
) (S) F closed when F vD + vR = v1 – V
F positive F Fig-b F then vD =0
and
vR = v1 – V
) (S) F open F vD F negative
and
vR = 0 F clipping the signal
) the battery shifts F signal down
and
) the diode cuts F signal off
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Ch(1) Signal Processing Circuits
Practice Problem 3-9
Homework
Common type of clipping
v2 = v1 Û v2 ∝ v1 Fup to V
(a) Desired transfer characteristic v2 versus v1
(b) Diode circuit
The bias voltage set F so that
) DA F conducts F v1 > VA
) DB F conducts F v1 < - VB
VR = v2 – v1 
When
- VB < v1 < VA
DA Û DB F don't conduct
V2 = v1 = vo
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Ch(1) Signal Processing Circuits
Clamping
‫ﺗﺜﺒﻴﺖ‬
Provide satisfactory pictures F TV receivers
The peak values F of F v(t) F clamped at
predetermined levels
In passing through amplifiers F dc reference level
F lost Û clamper F return F signal to its original form
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Ch(1) Signal Processing Circuits
R F small F C charge up to F +Vm of v1
When F +v1 change to -v1 F Vc = Vm F diode
prevents current flow in opposite direction
V2 = v1 - Vm
Signal form F unaffected
dc = Vm F positive peak F clamped at zero
If Vm F changes F Vc F changes F v2 again F
touches the axis
If D F reversed F - Vm F clamped at zero
If B F in series with D F the reference of v2 F VB
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Ch(1) Signal Processing Circuits
Clamping Û rectifying F related waveshaping
function F combination F D Û C
Rectifier
Variable component F rejected F dc value F
transmitted
Clamper
Variable component F transmitted dc value F
rejected
Homework F P.P F 3 – 10
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Ch(1) Signal Processing Circuits
Differentiating
Circuit (a) F provides F v2 derivative of v1
v2
∝
to
the capacitor charging current F in
response to a step of F rectangular wave F v1
Linear circuit transforms F rectangular wave
F
into F series of short pulse F if
RC F small F compared to F T F the period of the
input wave
General operation
Applying Kirchhoff's voltage law F to the left-hand
loop
v1 = vC + vR ≅ vC
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Ch(1) Signal Processing Circuits
vR small compared to vC
iC = C
∴
d vC
dt
v 2 = v R = Ri = RC
d vc
dt
≅ RC
d v1
dt
v2 ∝ F to the derivative F v1
Integrating
If differentiating is possible Fintegrating is also
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Ch(1) Signal Processing Circuits
Square wave of V F applied long enough F for
cyclic operation to be established
RC F little grater than F 1/2 T F of the square
wave
C F charged Û discharged F on alternate F
1/2 T F v2 F shown in Fig. b
If RC F large compared to F T
Only straight portion of the exponential F appears
∴
v2 F sawtooth wave ∝ time
In general
v1 = vR + vC ≅ vR = iR
If vC F small F compared to F vR F RC >T
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Ch(1) Signal Processing Circuits
1
v2 =
C
1
∫ idt ≅ RC
∫v
1
dt
V2 ∝ ∫ v1
Op Amp Integrator
General feed back network F contains C Û L Û R
C F feedback element
V1 ≅ 0
n F at ground potential
I1 ≅ 0
The sum of the I into n
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Ch(1) Signal Processing Circuits
dvo
v1
+C
=0
R1
dt
or
v1
dt
dvo = −
R1C
Integrating each term with respect to time and
solving
1
vo = −
R1C
∫ v dt
1
+ a consanct
This F an integrator device F very useful in computing
signal processing Û signal generating
Op Amp Differentiator
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Ch(1) Signal Processing Circuits
R Û C F interchanged F Differentiator device
The sum of the current
C1
dv1 vo
+ =0
dt R
solving
vo = −RC1
dv1
dt
Vo ∝ dvi
Differentiator device is not so useful as the integrator
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