Wiring Precautions of Video Amplifier Theory

The mechanical layout of the video amplifier is very important. All leads should be as short as possible. When using a printed circuit board, conductors should be wide and as short as possible. This helps provide low resistance and low inductance connections. In addition, stray signal coupling from the input to the output is minimized.

Grounding is the most important wiring precaution. As with all high frequency circuits, a ground plane and good grounding techniques should be used. The ground plane should connect all areas of the pattern side of the printed circuit board that are not otherwise used. The ground plane provides a low-resistance low-inductance common return path for all signal and power returns. The ground plane also reduces stray signal pick up.

Each power supply lead should have a bypass capacitor to ground as near as possible to the amplifier pins. A 0.1µF capacitor is normally sufficient. In very high-frequency and high-gain circuits, a combination of a 1µF tantalum capacitor in parallel with a 470-pF ceramic capacitor is a suitable bypass.

Single point grounding should be used in cases where point-to-point wiring is used or a ground plane is not used. The input signal return, the load signal return, and the power supply common should all be connected at the same physical point. This eliminates ground loops or common current paths which may cause signal modulation or unwanted feedback.

When designing video amplifier circuits, resistor values from 50Ω to 100Ω should be used for input terminations. Resistors in this range improve circuit performance by reducing the effects of device input capacitance and input noise currents.