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Block 5
Wave shaping Circuits
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3c. Identify Sawtooth Generator Operating
Principles
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SAWTOOTH
PURPOSE To produce a sawtoothwaveform. One input cycle will
produce
one output cycle.Also known as sweep, time/base,time/division,
seconds/division, or ramp
generator.
This circuit is considered a relaxation
oscillator.
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Parts of sawtooth waveform
Sweep time/electrical length
(Time allowed to charge)
Rest or flyback time (Discharge Time)
Physical length (Amplitude)
Slope (Rate of rise/percent of curve) PRT
PRF
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The Sawtooth Generator, produces a waveform that
will have a linear rise characteristic. RISE over RUN
SLOPE
2 2
2
1
1
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Simple Sawtooth Circuit
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100
90
80
70
60
50
40
30
20
10
0.5 1 2 3 4 5
CURVE RC CIRCUIT LR CIRCUIT
A
B
CAPACITOR VOLT AGEON CHARGE
INDUCTOR CURRENTOR RESISTOR VOLTAGEON BUILD-UP
CAPACITOR VOLT AGEON DISCHARGE
INDUCTOR CURRENTOR RESISTOR VOLTAGEON DECAY
RESISTOR VOLTAGEOR CAPACITOR CUR-RENT ON CHARGE ORDISCHARGE
INDUCTOR VOLTAGE ONBUILD-UP OR DECAY
A
B
0.5 1 2 3 4 5
AQR30020010-9307-999
TIME IN THE TIME CONSTANTS
Universal Time Constant Chart
Referring to theUniversal Time
Constant Chart,you will find thatthe most linearpart of the
curve
is the first 10%of the first timeconstant.
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Sawtooth Generator
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Purpose of Components
R1 Provides forward bias for Q1.
C1
Input signal coupling capacitorQ1 Serves as charge and
discharge
switch for the RC network consisting of
R2 and C2.
R2/C2 RC network that produces the
slope/ramp portion of the output wave.
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Sawtooth Generator Operation
C2 charges through R2 developingthe output slope when Q1 is
cutoffby the negative gate.
+1.2V
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Sawtooth Generator Operation
C2 discharges through Q1 when Q1issaturated (conducting) by
thepositive gate and this is the flyback
time.+1.2V
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Relationships
RC
teLengthNegativeGa
Amplitude
teLengthNegativeGaRCLinearity
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Gate Length Linearity
Relationship
TIME
GATE
INCREASE IN
GATE LENGTH
AMPLITUDE
A. INCREASING GATE LENGTH
TIME
GATE
DECREASE IN
GATE LENGTH
AMPLITUDE
B. DECREASING GATE LENGTH
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RC
Linearity Relationship
INCREASINGR OR C
AMPLITUDE
TIME TIME
GATE
A. INCREASING R or C
DECREASINGR OR C
AMPLITUDE
GATE
B. DECREASING R or C
AQR2E020010-9704-1119
Increases Linearity Decreases Linearity
Before After
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Block 5
Summary 3c
Parts of the Waveform
Sawtooth Generator components
Circuit operation
Parameter Changes
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Sawtooth Generator
Appraisal
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Sawtooth Generator
1. In the sawtooth generator circuit, a positive gateapplied to
the base of Q1 will ________ C2.
a. chargeb. discharge
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Sawtooth Generator
2. In the sawtooth generator circuit, the rate of voltagechange
across capacitor C2 is almost linear
during the first ____ of the capacitor charge time.a. 1%
b. 5%
c. 10%
d. 20%
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Sawtooth Generator
3. The linearity of the sawtooth waveform is controlledby
a. R2b. C2
c. negative input gate duration
d. all of the above
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Sawtooth Generator
4. A negative gate applied to the base of Q1 will_____ Q1 and
allow C2 to ______ through R2.
a. cutoff; chargeb. cutoff; discharge
c. saturate; charge
d. saturate; discharge
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Appraisal Answers
1. B
2. C
3. D4. A
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The End
