Video-Out Coupling Schematic Circuit Diagram

Utilizing Distribution Amplifiers for Multiple Video Destinations

When you aim to route a video signal to multiple destinations, employing a distribution amplifier becomes essential to align with the 75-ohm impedance of the video cable. The distribution amplifier acts by terminating the incoming cable at 75 ohms and furnishing several outputs, each with a 75-ohm output impedance. Typically, this configuration involves placing a 75-ohm series resistor in the output lead of each video opamp (current-feedback amplifier) to achieve the desired impedance match. Consequently, the opamps need to be configured for a gain of 2, ensuring an insertion gain of 1 (0 dB).

Enhancing Reliability with High Input Impedance Amplifiers

In the existing setup, a significant drawback emerges. If the amplifier or its power supply malfunction, no signal reaches any of the outputs. To address this issue, employing a high input impedance amplifier proves beneficial. Such an amplifier can be integrated into a video line without requiring its own 75-ohm termination resistor. To mitigate hum interference and voltage disparities between the cable screen and the circuit earth. The circuit leverages the opamp’s common mode rejection, enhancing overall reliability.

Optimizing Common-Mode Rejection and Bandwidth

The circuit’s common-mode rejection is fine-tuned using resistor RG1. Utilizing the LT1396 video opamp as indicated, an impressive common-mode rejection exceeding 40 dB can be achieved. Additionally, the signal bandwidth can be tailored to specific needs through the use of trim pots. The circuit attains a bandwidth of over 10 MHz, making it highly suitable for processing video signals. Moreover, thanks to the high-impedance connection to the video line, the video signal remains unaffected even when the power to the coupled amplifier is switched off.

Introducing LT1395/LT1396/LT1397 Amplifiers

The LT1395/LT1396/LT1397 amplifiers are advanced single/dual/quad 400 MHz current feedback amplifiers. With an impressive 800V/µs slew rate and the ability to drive up to 80mA of output current, these amplifiers operate across a wide range of supplies, from a single 4V to ±6V. At ±5V, each amplifier draws a modest 4.6 mA of supply current. Amplifiers, vital in various applications such as wireless communications, broadcasting, and audio equipment, serve the essential function of increasing the voltage, current, or power of a signal and can be broadly categorized as weak-signal amplifiers or power amplifiers.