BLOCKING OSCILLATORS AND TIMEBASE GENERATOR
1. Sketch & Define slope error and displacement error.
Slope error (or) sweep speed error (es):
Slope error is defined as the ratio of the difference in slope at beginning and end sweep to the initial value of the slope. It is also called as sweep speed error(es)
It is defined as the maximum difference between the actual sweep voltage and linear sweep which passes through the beginning and end points of the actual sweep.
The displacement error is given as
2. Mention two applications of blocking oscillators.
ü Used as a main device to supply triggers for synchronization of a system having pulse type waveforms
ü Used as a Frequency Divider or Counter
ü Used to produce large peak power pulses.
ü As a low impedance switch
3. State any two applications of pulse transformer.
· To act as a coupling element in certain pulse generating circuits such as blocking oscillators
· To invert the polarity of pulse
· To provide dc isolation between source and a load
· To produce pulse in a circuit having negligible dc resistance
· To differentiate a pulse
4. What are 'Restoration time' and 'Sweep time' of a time base signal?
Restoration time (Tr):
It is the time required for the return to its intial value. It is also called as return time or flyback time.
It is the period during which voltage increases linearly
5. List the applications of time base generators.
· Used in CRO(Cathode Ray Oscilloscope)
· Used in Television and radar displays
· Used in precise time measurements
· Used in time modulation
6. What are tha advantages of core saturation method of frequency control in a blocking oscillator?
The pulse duration depends on the supply voltage and characteristics of the core and not on the transistor parameters (hfe).
The pulse width is given by
7. State any two methods of achieving sweep linearity of a time-base waveform.
ü Exponential charging
ü Constant current charging
ü Miller circuit
ü Bootstrap circuit.
8. Draw the equivalent circuit of a pulse transformer. Name the various elements in it.
R1=Primary winding and source resistance
R2=Total resistance reflected to primary side
C=Total effective shunt capacitance
9. What is the function of time base circuit?
A linear time base generator produces an output waveform, which produces a portion which exhibits a linear variation of voltage or current with respect to time.
10. What is blocking oscillator?
The circuit which uses a regerative feedback, producing a single pulse or pulse train is called a blocking oscillator.
11. Which are the two important elements of a blocking oscillator?
1. Active element like transistor.
2. A pulse transformer.
12. What is the function of pulse transformer in blocking oscillator?
A pulse transformer is used to couple output of the transistor back to the input.The nature of such feedback through pulse transformer is controlled by relative winding polarities of a pulse transformer.
13. What is pulse transformer?
A pulse transformer is basically a transformer which couples a source of pulses of electrical energy to the load, keeping the shape and other properties of pulses unchanged.The voltage level of the pulse can be raised or lowered by designing the proper turns ratio for the pulse transformer.
14. Draw a transistorized bootstrap time base generator circuit?
15. Draw the circuit diagram of astable blocking oscillator.
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