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Transcript
DELAY TIME In many pulse circuit applications, it is necessary to delay a signal a certain amount of time called delay time. Delay circuits may be classified in two main groups: electronic circuits(e.g mono stable multi vibrator and blocking oscillator elc.)and electromagnetic delay lines. • The electronic circuits operate on the principle of being in a stable until triggered by a pulse. Then they shift to a quasi stable state for a period of time determined usually by the constant or RC circuit. After this period of time, the circuit returns against to its stable state until triggered again by another pulse. If some means is provided to have a pulse generated at a time the circuit returns to its stable state, a time delay circuit results. The output pulse is not necessarily an exact reproduction of the input pulse. Its amplitude and width are dependent upon the circuit producing it and not on the amplitude and width of the input pulse. Types of delay lines • Electronic types • electromagnetic type Electromagnetic delay lines • Electromagnetic delay lines may be further classified as distributed parameter or lumped parameter delay lines. The distributed parameter line more closely approaches a transmission line, whereas the lumped parameter line resembles a filter. Delay ranging from a few nanoseconds to hundreds of micro-seconds are obtainable with electromagnetic lines. For longer delays acoustic delay lines and storage devices are used. Acoustic delay lines employ acoustic wave propagation and electro-mechanical transducers at the input and output. Lumped parameter delay lines • Consists of a number of inductors and capacitors , the inductors are connected in series and the capacitors are through the junction between the inductors to the ground . Distributed Parameter Delay lines • Normally all transmission lines consists of pair of straight conducting wires or coaxial cables. ELECTRONIC DELAY LINE • Electronic delay line is an electronic circuit used to delay a pulse waveform ,Any monostable circuit may be used for this purpose. the input pulse is used to trigger the monostable circuit, the output is generated by the monostable circuit itself • The amplitude and duration Tp of the output pulse is controlled by the monostable circuits . • Hence,a monostable circuit can be used as pulse delay device as well as pulse reshaping device. monostable multivibrator • monostable multivibrator is an electronic circuit that generates an output pulse. When triggered, a pulse of pre-defined duration is produced. The circuit then returns to its quiescent state and produces no more output until triggered again. Monostable multivibrator as atime delay device • The most popularly used circuit as an electronic delay line is the monostable multivibrator . • The monostable multivibrator should be triggered by the negative going edge of the input pulse. • The normally ON transistor at the same time voltage at Vo changes from Vce ON to Vcc it stay at Vcc depends upon the time constant C1R1.if pulse width time tp1 become equal to tp2 and amplitude of both input and output pulses also become equal then the pulse become delay by (one bit time) time tp Uses of delay lines • Delay line are used in distributed amplifiers cathode ray oscilloscope pulse coder and decoder ,measuring instrument ,radar , TV system and computers. CATHODE RAY OSCILLOSCOPE • CRO is an extremely useful and versatile laboratory instrument used for the measurement and analysis of waveforms and other phenoena in electronic circuits. major subsystem of a general purpose CRO consists of the following • 1. Cathode ray tube • 2. Vertical amplifier • 3. Delay line:this circuit is used to, delay the signal for a period of time in the vertical section of CRT • 4. Time base circuit • 5. Horizontal amplifier • 6. Trigger circuit • 7. Power supply. FUNCTION OF DELAY LINE • The diagram shows that when the delay line is not used, the initial part of the signal is lost and only part of the signal is displayed. DUAL TRACE CRO • Two different input signals are used is Channels A & B with attenuators and preamplifiers.A delay line is used between electronic switch & vertical amplifier that alternately connects the input to main vertical amplifiers. .There are two common operating mode for electronic switch called as • 1. Alternate mode • In this mode , the CRO spot traces channel A signal on one sweep & channel B on next . These signals have calibrated input attenuators and vertical position control and also amplitude of these signals can be adjusted individually and two images are placed separately on the screen. • 2. Chop mode • This mode is used for higher frequencies say of order 100kHz •THE END