Paralleling Amplifiers and Transmission Lines for Driving Capacitive Loads Fast

Certain video and other technologies require driving planar conductive surfaces fast. Unfortunately, the surfaces can have high capacitance, which means that driving them fast takes high currents. This complicates the amplifier design but the situation extends beyond just the amplifier. Between the amplifier and the capacitive load, there is necessarily some length of transmission line.

Most engineers are familiar with the use and design of transmission lines of 50 or 75 Ohms or 100 Ohms. Such impedances can be immediately problematic from at least two perspectives. First, when driving a capacitive load the transmission characteristic impedance necessarily creates an RC, limiting speed. Second, the characteristic impedance necessarily dictates the ratio of voltage to current during propagation. The specified settling time at the capacitive load may dictate currents that are simply impractical in a normal transmission line. This video shows you how to design a fast capacitive load driver through the use of distributed parallel LT1397 amplifiers and aggressive transmission line design.

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