--- title: "CRO block diagram and working" subject: "Basic Electronics Engineering" chapter: 7 key: "semester_2/basic_electronics_engineering:cro-block-diagram" source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/cro-block-diagram site: BCT Engineering --- # CRO block diagram and working Basic Electronics Engineering · Chapter 7: Application of Electronic System - Asked in: 2067 Chaitra, 4 marks - Video: [Cathode Ray Oscilloscope ( CRO )- Block Diagram - CRT](https://www.youtube.com/watch?v=X2lqQzi4b9w) — EzEd Channel - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/cro-block-diagram - Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-7 ## Question Draw the block diagram of (CRO) oscilloscope. And explain its working function. ## Short answer A CRO displays voltage vs. time on a CRT. The input signal is amplified and applied to vertical deflection plates, while a triggered time-base generator produces a sawtooth sweep for horizontal plates. The electron beam traces the waveform on the phosphor screen, allowing measurement of amplitude, period, and frequency. ## Answer The **cathode-ray oscilloscope (CRO)** displays a time-varying voltage as a waveform on a screen: voltage on the Y-axis and time on the X-axis. #### Block diagram ```text +----------+ +-----------+ Input signal --->| Attenuator|->| Vertical |---> Y-plates +----------+ | amplifier | | | +-----------+ [CRT] +----v-----+ +-----------+ | | Trigger |-->| Time-base |---> X-plates | circuit | | generator | (Horizontal +----------+ +-----------+ amplifier) Power supply (HV for CRT, LV for circuits) ``` #### Working 1. The input signal passes through an attenuator and the **vertical amplifier**, which raises it to a level high enough to deflect the electron beam; it is then applied to the vertical (Y) deflection plates. 2. The **trigger circuit** takes a sample of the signal (or an external trigger) and starts the sweep at the same point of each cycle, so the picture is stable. 3. The **time base generator** produces a sawtooth voltage. After the horizontal amplifier, it goes to the X plates and moves the beam uniformly from left to right, then quickly back. 4. In the **CRT**, the electron gun emits a focused beam, which strikes the phosphor screen and makes a bright spot. The vertical plates move it up and down with the signal, and the horizontal plates move it across with time. Together, the spot traces the waveform. 5. The **power supply** gives high voltage (kV) to the CRT and low voltages to the circuits. Measurements: voltage (amplitude), time period T, frequency f = 1/T, and phase difference. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. The signal being displayed is applied to which plates (after the vertical amplifier)? A. Vertical (Y) deflection plates B. Horizontal (X) plates C. The electron gun D. The screen Answer: A. The input signal moves the beam up and down through the Y plates. (Key point: Vertical deflection) 2. What is applied to the X plates to move the beam across the screen? A. The input signal B. A DC level C. A sawtooth voltage from the time base generator D. A square wave from the trigger Answer: C. The sawtooth moves the beam uniformly from left to right and quickly back. (Key point: Time base) 3. Which block makes the picture stable? A. Attenuator B. Trigger circuit, which starts the sweep at the same point of each cycle C. Power supply D. Phosphor screen Answer: B. Starting the sweep at the same point of every cycle makes the waveform overlap exactly. (Key point: Stable display) 4. If the period of a waveform read on the CRO is T, the frequency is: A. f = T B. f = T^2 C. f = 2T D. f = 1/T Answer: D. Frequency is the reciprocal of the time period, f = 1/T. 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