CRO Time Base Generator – Function | New Topic

In this note, we are going to know about CRO Time Base Generator and Function of Time Base Generator in CRO. Welcome to Poly Notes Hub, a leading destination for engineering notes for diploma and degree engineering notes.

Author Name: Arun Paul.

About CRO Time Base Generator

A Time Base Generator in CRO (Cathode Ray Oscilloscope) produces a sweep signal that travels the electron beam horizontally across the screen at a consistent speed. This guarantees that the waveform seen on the screen is correct and proportional to time.

The time base generator is required in a CRO for proper time-based signal representation, which ensures that waveforms are displayed correctly in relation to time.

There are two types of time base generator in CRO –

• RC Time Base Generator: It is used in low frequency applications.
• Miller Time Base Generator: It is used in high frequency applications.

CRO Time Base Generator Circuit Diagram

Here is the circuit diagram of time base generator in CRO –

CRO Time Base Generator Working Principle

A continuous sweep CRO using a Uni Junction Transistor or UJT as a time base generator as shown in the above diagram. The UJT or Uni Junction Transistor is used to produce the sweep. When the power is first applied the UJT is off and C_T charges through R_T. The UJT emitter voltage (V_E) rises towards V_BB when V_E reaches the peak voltage. The emitter to base “1” (B1) diode become forward biased and the UJT triggers ON. This provides a low resistance discharge path and the capacitor discharges rapidly. The emitter voltage V_E reaches the minimum value rapidly and the UJT goes off. The capacitor recharges and the cycle repeats.

To improve sweep linearity, two separate voltage supplies are used, a low voltage supply for UJT and high voltage supply for R_TC_T circuit.

CRO Time Base Generator Waveform

Function of Time Base Generator in CRO

Here we have listed some important function of time base generator in CRO –

1. The time base generator generates a sawtooth waveform that moves the electron beam from left to right at a constant speed.
2. The linear increase in voltage ensures that the beam sweeps across the screen at a constant rate, making the time axis uniform.
3. After reaching the end of the screen, the beam must return to the starting position quickly. The flyback period (retrace) is made invisible by blanking the beam to avoid unwanted distortions.
4. The time base generator can be synced with the input signal to keep the waveform stable and avoid drift.
5. The user can control the sweep speed (time per division) to adjust the display according to different signal frequencies.

Need of Time-Base Generator in CRO

Here we have listed some applications of the circuit in CRO –

• It moves the electron beam at a constant speed for accurate time representation.
• It is used to control sweep speed for signal analysis at various time scales.
• This circuit also stabilizes repeating waves on the screen.
• Blanks the beam during retrace to prevent distortion.
• Allows for the examination of signals with varying frequencies.