Draw and explain the block diagram of general purpose CRO.
1 Answer

The major block circuit is shown in the fig below for a general purpose CRO, is as follows:

  • CRT
  • Vertical Amplifier
  • Delay line
  • Time Base
  • Horizontal amplifier
  • Trigger Circuit
  • Power Supply

The function of various blocks is as follows


This is cathode ray tube which emits electrons that strikes the phosphor screen internally to provide a visual display of signal.

Vertical Amplifier:

This is wide band amplifier used to amplify signals in the vertical section.

Delay Line:

It is used to delay the signal for some time in the vertical sections.

Time Base:

It is required to generate the sawtooth voltage required to deflect the beam in the horizontal section.

Horizontal Amplifier:

This is used to amplify the sawtooth voltage before it is applied to horizontal deflection plates.

Trigger Circuit:

This is used to convert the incoming signal into trigger pulses so that the input signal and the sweep frequency can be synchronized.

Power Supply:

There are two power supplies a negative high voltage and a positive low voltage. The two voltages are generated in the CRO.The positive low volt supply is from +300 to 400V.The negative high voltage supply is from -1000 to -1500 volts. This voltage passed through a bleeder resistor at a few mA. The intermediate voltages are obtained from the bleeder resistor for intensity focus and position control.

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