寄生振荡（Parasitic oscillation）.doc

寄生振荡（Parasitic oscillation） For example, the interference caused by positive feedback Amps A tube is composed of a plurality of vacuum tubes, between circuits and components at all levels will inevitably exist in electric, magnetic and electromagnetic And other parasitic feedback through which these outputs are coupled to the control gate of the input stage. This is known to all Parasitic feedback degrades the amplifiers technical specifications and performance, and even amplifies the amplifiers power. So in the tube, the Parasitic feedback at all levels of the circuit must be reduced to the extent that it does not affect the performance and performance of the amplifier. 1. capacitive coupling In any two amps components and wires are asked distributed capacitance, audio signals pass through these capacitance from high potential to Low potential, for example, from the power amplifier output stage coupled to the first level control gate circuit, as shown in figure 7. In Figure 7, when the distribution of capacitive coupling between the input and output of AMPS, is equivalent to adding a parallel in the tube in The feedback voltage is the feedback factor of the feedback signal: The Z is the input impedance of the feedback circuit, and the C0 is the distributed capacitance of the feedback network. In order not to affect the normal work of the parasitic feedback amps, must reduce the distributed capacitance (1/5 ~ 1/10), which is not allowed More than (1 ~ 2) * 103pF, it should be paid more attention in the assembly, between the output stage and the distance to the input stage Far away, the components at all levels and the same level of vacuum tubes together, do not mix and fall, ground suspension applications The method is separated by metal plates at all levels, and the bare copper wires are enclosed by one ring in the vacuum, and the other end is welded on the bottom plate, This allows parasitic feedback to be reduced. Parasitic oscillation analysis The parasitic osci