06-08-2013, 02:47 PM
TIME BASE GENERATORS
TIME BASE .ppt (Size: 839.5 KB / Downloads: 94)
INTRODUCTION
Circuits which is used to generate a linear variation of voltage with time are called voltage time base generators.
Circuits which produce a current which linearly increases with time are called current time base generators.
Since these circuits provide an output waveform which exhibits a linear variation of voltage with time are called linear time base generators.
Important application is in CRO which is used to sweep the electron beam horizontally across the screen is called sweep circuits.
Errors of generation of sweep waveform
There are three most commonly used measures of sweep voltage:
Sweep speed error
Displacement error
Transmission error
These are called sweep parameters.
Sweep Speed Error (es):
Sweep generator to keep sweep speed (rate of change of sweep voltage with time)constant. Any change in sweep speed deviates sweep voltage from maintaining linear slope. The error due to sweep speed is called sweep speed error or slope error.
Boot strap circuit: A const. current is obtained by maintaining nearly const. voltage across a fixed resistor in series with a capacitor.
Compensating network: A compensating circuit is added to improve the linearity of the bootstrap & the miller time base generators.
Inductor circuit: Linear capacitor charging is achieved by introducing RLC series circuit.
practical bootstrap sweep circuit
Point A in fig(b) will exactly follow point B. This bootstrap action results vol drop across pt A &B const. hence iR is const.since this const current is used to charge C increases linearly with time