Monday, January 19, 2015

Answers to questions and summary of waveforms and wave generators.

SUMMARY

This chapter has presented information on waveforms and wave generators. The information that follows summarizes the important points of this chapter.

A waveform which undergoes a pattern of changes, returns to its original pattern, and repeats that same pattern of changes is called a PERIODIC waveform.

Each completed pattern of a waveform is called a CYCLE.

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A SQUARE WAVE is identified by, two alternations equal in time that are square in appearance. One alternation is called a PULSE. The time for one complete cycle is called the PULSE REPETITION TIME (prt). The number of times in one second that the cycle repeats itself is called PULSE REPETITION RATE (prr) or PULSE REPETITION FREQUENCY (prf). The length of the pulse measured in the figure (T0 to T1) is referred to as the PULSE WIDTH (pw). The left side of the pulse is referred to as the LEADING EDGE and the right side as the TRAILING EDGE.

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A RECTANGULAR WAVE has two alternations that are unequal in time.

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A SAWTOOTH WAVE has a linear increase in voltage followed by a rapid decrease of voltage at the end of the waveform.

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A TRAPEZOIDAL WAVE looks like a sawtooth wave sitting on top of a square wave. The leading edge is called the JUMP voltage.

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A TRIGGER is a very narrow pulse used to turn on or off another circuit.

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A MULTIVIBRATOR is used to generate a square or rectangular wave. A multivibrator is basically two amplifiers with regenerative feedback.

The ASTABLE MULTIVIBRATOR has no stable state. The transistors alternately switch from cutoff to saturation at a frequency determined by the RC time constants of the coupling circuits.

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The MONOSTABLE MULTIVIBRATOR has one stable state. One transistor conducts while the other is cut off. An external trigger must be applied to change this condition.

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The BISTABLE MULTIVIBRATOR has two steady states. It remains in one of the stable states until a trigger is applied. It then switches to the other stable state until another trigger is applied.

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The bistable multivibrator is also known as a FLIP-FLOP. The two inputs are SET and CLEAR. The two outputs are "1" and "0." A trigger pulse on the set input will cause the "1" output (negative or positive voltage depending on the type transistor used). At the same time the "0" output will equal 0 volts. This is the SET state.

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A CLEAR STATE of a flip-flop exists when the "1" output measures low voltage (or 0 volts) and the "0" output is high voltage. The flip-flop will flop to the CLEAR state only upon application of a trigger pulse to the CLEAR (C) input.

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There is a third lead on some flip-flops. This lead is the TOGGLE (T) input. Every time a trigger pulse is applied to the (T) input, the flip-flop will change states.

BLOCKING OSCILLATORS are used in applications which require a narrow pulse with sharp leading and trailing edges. They are used as TRIGGER GENERATORS or FREQUENCY DIVIDERS.

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A SAWTOOTH GENERATOR voltage waveform has a linear change in voltage and a fast recovery time. The linear change in voltage is generated by taking the output from a capacitor. The sawtooth voltage waveform is used to provide electrostatic deflection in oscilloscopes.

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A TRAPEZOIDAL GENERATOR voltage waveform is used to provide, a linear increase in current through a coil. A trapezoidal wave begins with a step or jump voltage, then a sawtooth wave. A trapezoidal wave of voltage is used in electromagnetic deflection display devices.

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ANSWERS TO QUESTIONS Q1. THROUGH Q14.

A1. Multivibrator.

A2. Astable.

A3. Monostable.

A4. Bistable.

A5. RC coupling networks.

A6. One-shot.

A7. Two.

A8. Two.

A9. SET state. A10. Transformer.

A11. Ten percent.

A12. Decreases linearity.

A13. To allow the capacitor time to discharge. A14. A resistor.