Ch(1) Signal Processing Circuits
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WAVESHAPING CIRCUITS Major virtue of electronic circuits the ease of
Controlled Voltage current waveforms Some of the basic waveshaping functions
radar pulse – train generator
Ch(1) Signal Processing Circuits
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Clipping تشذيب
Removing undesired portion of a signal The waveshape function performed by the circuit components arranging
Consisting diode resistance voltage source
Input signal V1 varies with time Output signal VD VR The sum of the voltage around the loop = zero
vD + vR = v1 – V
vR = v1 – V - vD
vD = v1 – V - vR
Ch(1) Signal Processing Circuits
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The behavior of the circuit depends on the state of the diode switch (S)
(S) closed when vD + vR = v1 – V
positive Fig-b then vD =0 and
vR = v1 – V
(S) open vD negative
and
vR = 0 clipping the signal the battery shifts signal down
and
the diode cuts signal off
Ch(1) Signal Processing Circuits
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Practice Problem 3-9 Homework
Common type of clipping
v2 = v1 v2 ∝ v1 up to V
(a) Desired transfer characteristic v2 versus v1 (b) Diode circuit
The bias voltage set so that DA conducts v1 > VA DB conducts v1 < - VB
VR = v2 – v1
When - VB < v1 < VA
DA DB don't conduct V2 = v1 = vo
Ch(1) Signal Processing Circuits
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Clamping تثبيت
Provide satisfactory pictures TV receivers The peak values of v(t) clamped at
predetermined levels In passing through amplifiers dc reference level lost clamper return signal to its original form
Ch(1) Signal Processing Circuits
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R small C charge up to +Vm of v1 When +v1 change to -v1 Vc = Vm diode prevents current flow in opposite direction
V2 = v1 - Vm
Signal form unaffected
dc = Vm positive peak clamped at zero
If Vm changes Vc changes v2 again touches the axis
If D reversed - Vm clamped at zero
If B in series with D the reference of v2 VB
Ch(1) Signal Processing Circuits
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Clamping rectifying related waveshaping function combination D C
Rectifier
Variable component rejected dc value
transmitted Clamper
Variable component transmitted dc value
rejected
Homework P.P 3 – 10
Ch(1) Signal Processing Circuits
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Differentiating
Circuit (a) provides v2 derivative of v1
v2 ∝ to the capacitor charging current in
response to a step of rectangular wave v1
Linear circuit transforms rectangular wave
into series of short pulse if
RC small compared to T the period of the
input wave
General operation Applying Kirchhoff's voltage law to the left-hand
loop v1 = vC + vR ≅ vC
Ch(1) Signal Processing Circuits
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vR small compared to vC
v2 ∝ to the derivative v1
Integrating
If differentiating is possible integrating is also
dtd
RCdtd
RCRivv
dtd
Ci
vvR
vC
c
C
12 ≅===∴
=
Ch(1) Signal Processing Circuits
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Square wave of V applied long enough for cyclic operation to be established RC little grater than 1/2 T of the square wave C charged discharged on alternate 1/2 T v2 shown in Fig. b If RC large compared to T
Only straight portion of the exponential appears
∴ v2 sawtooth wave ∝ time
In general v1 = vR + vC ≅ vR = iR
If vC small compared to vR RC >T
Ch(1) Signal Processing Circuits
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V2 ∝ ∫ v1
Op Amp Integrator
General feed back network contains C L R
C feedback element
V1 ≅ 0
n at ground potential
I1 ≅ 0
The sum of the I into n
∫ ∫≅= dtvRC
idtC
v 1211
Ch(1) Signal Processing Circuits
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Integrating each term with respect to time and solving
This an integrator device very useful in computing signal processing signal generating
Op Amp Differentiator
dtCRvdvor
dtdvC
Rv
oo
1
1
1
1 0 −==+
∫ +−= consanctadtvCR
v o 11
1
Ch(1) Signal Processing Circuits
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R C interchanged Differentiator device The sum of the current
Vo ∝ dvi
Differentiator device is not so useful as the integrator
dtdvRCvsolving
Rv
dtdvC o
o 11
11 0 −==+