Vertical amplifier

The sensitivity (gain) and frequency bandwidth (B.W) response characteristics of the oscilloscope are mainly determine by the vertical amplifier .Since the gain-B W. product is constant, to obtain a greater sensitivity the B.W. is narrowed, or vice-versa.
Some oscilloscopes give two alternatives, switching to a wide bandwidth position, and switching to a high sensitivity position.

Block Diagram of a Vertical Amplifier 

The vertical amplifier consists of several stages, with fixed overall sensitivity gain expressed in V/div. The advantage of fixed gain is that the amplifier can be more easily designed to meet the requirements of stability and B.W. The vertical amplifier is kept within its signal handling capability by proper selection the input attenuator switch. The first element of the pre-amplifier is the input stage, often consisting of a FET source follower whose high input impedance isolates the amplifier from the attenuator.
This FET input stage is followed by a BJT emitter follower, to match the medium impedance of FET output with the low impedance input of the phase inverter.
This phase inverter provides two anti phase output signals which are required operate the push- pull output amplifier. The push-pull output stage delivers equal signal voltages of opposite polarity to the vertical plates of the CRT. The advantages of push-pull operation in CRO are similar to those obtained from push-pull operation in other applications; better voltage cancellation ran the source or power supply (i.e. dc), even harmonic suppression, especially large 2nd harmonic is cancelled out, and greater power output per tube as a suit of even harmonic cancellation. In addition, a number of defocusing and non linear effects are reduced, because neither plate is at ground potential.

HORIZONTAL DEFLETING SYSTEM

The horizontal deflecting system 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 CT charges exponentially through RT. The UJT emitter voltage VE rises towards VBB and when VE reaches the peak voltage VP, as shown in Fig. 4.3, 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 VE 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 RTCT circuit. 

RT is used for continuous control of frequency within a range and CT 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.