The Cause and Eliminate Method of Self-excited Oscillation in Long Cable Amplifier Circuits

Abstract

SMA long cable distributed capacitance is easy to trigger broadband amplifier circuit’s self-oscillation. In this study we design an amplifier circuit based on OPA691 chip, discuss the influence of long cable’s distributed capacitance, then prompt a solution to add 50Ω compensation resistor between the output terminal and the load capacitance. According to the Tina simulation analysis, when 50Ω compensation resistor is added, bode diagrams show amplitude characteristic is smaller than 0 dB at -180 ° phase. The selfoscillation also disappeared in actual circuit measurement, which verify the rationality of this solution.