This is one of the topic from e&tc syllabus of diploma students. Hope the ppt will help them to understand the concepts better.

1. TYPES OF
TIME BASE GENERATORS
1) UJT as RELAXATION OSCILLATOR.
2) MILLER SWEEP GENERATOR.
3) BOOTSTRAP RAMP GENERATOR.
4) CURRENT TIME BASE
GENERATOR.

2. UJT as RELAXATION OSCILLATOR

3. Equivalent circuit.
 Discharging of capacitor through UJT generates saw-
tooth waveform.
 When VBB is connected, it will start charging the
capacitor through R1.
 The capacitor keeps on charging until the voltage
across it becomes equal to 0.7V .

4.  We take output across the capacitor ‘C’.
 During the charging process, the voltage across
capacitor increases until it reaches its peak value.
 At the peak value the UJT is switched ON and it
starts conducting.

5.  When the UJT starts conducting , the capacitor
starts discharging between emitter and B1.
 When the capacitor voltage become zero, the
capacitor again starts charging.
 The frequency of the o/p saw-tooth waveform can
be varied by changing the value of R1 resistor, since
this controls the time constant(R1C) of the
capacitor charging circuit.
FORMULA
 t=2.3R1Clog10(1/1-ŋ)
 t=R1Cloge(1/1-ŋ)
 VC=VBB[1-e^(-t/R1C)]

6. MILLER SWEEP GENERATOR

7.  Q1 acts as a switch and Q2 acts as a CE configuration
high gain amplifier.
 When Q1 is ON, Q2 is OFF.
 At this instance o/p voltage across capacitor is
equal to VCC.
 If a pulse of negative polarity is applied, then Q1 is
reverse biased and it is switched OFF. Q2 then is
switched ON.
 Since Q2 conducts, o/p voltage begins to decrease
towards zero.
 When the i/p pulse is removed the capacitor again
begins to charge.

8. FORMULA
 tS=CRC(β+1)
where tS=sweep time(rising time).

9. BOOTSTRAP RAMP GENERATOR

10.  The transistor Q1 acts as a switch and Q2 as an unity
gain amplifier.
 Suppose the transistor Q1 is ON and Q2 is OFF.
 The capacitor C1 begins to charge to VCC through the
diode forward resistance RE.
 At this instant, the output voltage Vo is zero.
 When negative pulse is applied to the base of transistor
Q1, it turns OFF.
 The output voltage (Vo) is the same as the base voltage
of transistor Q2.
Diode is reversed biased. Capacitor ‘C’ starts charging.
 Output voltage begins to increase from zero.

11.  Since the value of capacitor C1 is much larger than that
of capacitor C, therefore the voltage across capacitor
C1 practically remains constant.
 Thus the voltage drop across the resistor R also remains
constant because of this, the current iR through the
resistor also remains constant.
 This causes the voltage across the capacitor C (and
hence the output voltage) to increase linearly with time.

12. CURRENT TIME BASE GENERATOR

13.  There are 3 important blocks-constant current source,
capacitor and a switch.
 During the sweep interval, the capacitor ‘C’ is charged by
the constant current.
 When the sweep waveform reaches to its maximum
value VS the switch opens and does not allow the current
to flow further.
 The capacitor ‘C’ starts discharging.
 The o/p voltage waveform is measured across the
capacitor.