Horizontal Deflection System in CRO:

The Horizontal Deflection System in CRO consist of a Time Base Generator and an output amplifier.

Sweep or Time Base Generator:

A continuous sweep CRO using a UJT as a time base generator is shown in Fig. 7.8. The UJT is used to produce the sweep. When the power is first applied, the UJT is off and the C_T changes exponentially through R_T. The UJT emitter voltage V_E rises tow­ards V_BB and when V_E reaches the peak voltage V_P, as shown in Fig. 7.9, the emitter to base ‘1’ (B₁) diode becomes 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 a high voltage supply for the R_TC_T circuit.

R_T is used for continuous control of frequency within a range and C_T is var­ied or changed in steps for range changing. They are sometimes called as timing resistor and timing capacitor respectively.

The sync pulse enables the sweep frequency to be exactly equal to the input signal frequency, so that the signal is locked on the screen and does not drift.