Video Signal Emphasizer and Amplifier Circuit

Figure 1 

The construction of the circuit was focused on emphasizing and amplification of video signals to obtain more clarity of picture frequencies.

• BC547 – NPN small signal transistors designed for general purpose switching and amplification due to its low voltage, low current and three different gain selections
• 1N4148 – a small-signal silicon epitaxial planar diode used for fast switching applications with a reverse voltage of 100 V and forward current of 150 mA

In a video output, the high signal of picture frequency is selected for amplification to provide a more fine output. This is made possible by placing the circuit between the video unit and the reception input where the video plug of television receiver is inserted. The construction is done by simply utilizing the operation of three transistors, instead of ICs, and other supporting components.

An isolator operates in the first stage of Q1, which provides an interface for the input impedance. Q2 handles the second stage where it conducts in common base configuration. In this stage, the 250 ohm trimmer TR2 determines the gain of the circuit. To regulate TR2, it should be positioned where an output voltage of 1 Vp-p is present, with a 75 ohm load. The frequency response is being regulated by the combination of R6, C3, and 500 ohm TR1. An output buffer is performed by Q3 in the third stage, providing a line driver of 75 ohms. The supply of the circuit is well stabilized with 12 V and 50 mA.

Figure 2 

The theory of the circuit can be used in signal processing system for use in television formats like PAL, pseudo-SECAM, and NTSC. This is to ensure the improvement of performance and rationalization in the design of VCRs through the use of digital technology. This process will provide more benefits to millions of users who are habitually watching videos, movies, and television programs.

Source:users.otenet.gr/~athsam/video_signal_emphasis.htm