sweep

The diode D13 is responsible for providing different timings for the forward sweep and the retrace, with the retrace occurring at a faster rate than the forward sweep. It generates outputs that inform the blanking circuit when to blank and unblank the cathode ray tube (CRT). The sync trigger input delivers pulses that synchronize the beginning of the sweep to the voltage level chosen by the user. Additionally, the sync trigger input continuously retriggers a 74123 retriggerable one-shot, ensuring that pin 4 of U9 remains in a high state. If the synchronized trigger is not activated due to the input signal not reaching the selected sync level, the retriggerable one-shot will time out, allowing the sweep generator to operate in a free-running mode. A truth table for the 7476 is essential for analyzing this circuit and is provided in the accompanying table.

The circuit described involves several critical components that work in tandem to manage the timing and synchronization of the CRT's sweep operations. The diode D13 plays a pivotal role in differentiating the timing sequences for the forward sweep and the retrace. The forward sweep is typically slower, while the retrace, which is the return of the electron beam to the starting position, can occur more rapidly. This functionality is crucial for maintaining a stable and flicker-free display.

The outputs generated by D13 are directed to a blanking circuit, which controls the visibility of the CRT's output. The blanking circuit ensures that the CRT does not display any unwanted artifacts during the retrace period by effectively turning off the beam when necessary. This is essential for achieving a clean visual output.

The synchronization of the sweep is managed through the sync trigger input, which receives pulses that dictate the timing of the sweep initiation. The ability to synchronize the sweep to a user-selected voltage level enhances the versatility of the circuit, allowing it to adapt to different input signals and display requirements.

The 74123 retriggerable one-shot timer is a critical component in maintaining the timing integrity of the sweep generator. By continuously retriggering, it ensures that pin 4 of U9 remains high, which is necessary for proper operation. In scenarios where the sync trigger is not activated—perhaps due to the input signal being below the required threshold—the one-shot will eventually time out. This timeout allows the sweep generator to enter a free-running mode, which may be beneficial in certain applications where synchronization is not critical.

In addition to these components, the truth table for the 7476 flip-flop is an invaluable tool for analyzing the circuit's behavior. It provides insight into the logic states and transitions that occur within the circuit, enabling engineers to troubleshoot and optimize performance effectively. The truth table outlines how different input combinations affect the output states, which is crucial for ensuring reliable operation in a variety of scenarios. Overall, the described circuit is a sophisticated assembly of components that work together to deliver precise control over the CRT's display timing.Diode, D13, provides different timings for the forward sweep, and the retrace which can be faster than the forward sweep. Outputs are generated to tell the blanking circuit when to blank the CRT and when to unblank the CRT.

The sync trigger input provides pulses that synchronize the start of the sweep to the voltage level selected by the user. The sync trigger input constantly retriggers a 74123 retriggerable one-shot so that pin 4 of U9 is always high. If synchronized trigger is not selected because the value of the input signal never reaches the selected sync level, then the retriggerable one-shot will time out allowing the sweep generator to free-run.

A truth table for the 7476 is vital for analyzing this circuit and is given in the table below. 🔗 External reference