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大模块的交叉反馈线路中有正反馈。
http://www.douglas-self.com/ampins/balanced/balanced.htm
准浮动输出使用的电路相当精细，电流和电压的正负反馈混合在一起。这种方法可以很好地实现所需的功能；唯一的缺点是容易增加电路容差，因此通常需要一个预设电阻来设置输出为等幅度；通常的布置如图6所示。如果未正确调整平衡预设，输出的一侧将先于另一侧削波，从而减少总输出裕量。出厂设置后，无需再操作该预设值，除非更换电路中的电阻；更改运算放大器不会产生任何影响。平衡网络由一个负载电阻组成，每个输出端接地；在这方面，输出特性与真正的浮空输出不同，后者完全与地隔离。这些负载电阻低于典型平衡输入的输入阻抗，因此，如果使用输入阻抗不相等的简单差分放大器（参见下面的线路输入部分），输出平衡不会受到严重干扰，冷热输出的削波仍保持对称。
Quasi-floating outputs use a rather subtle circuit with an intimate mixture of positive and negative feedback of current and voltage. This performs the required function admirably; its only drawback is a tendency to accentuate circuit tolerances, and so a preset resistor is normally required to set the outputs for equal amplitude; the usual arrangement is shown in Fig 6. If the balance preset is not correctly adjusted one side of the output will clip before the other and reduce the total output headroom. After factory setting this preset should not need to be touched unless the resistors in the circuit are replaced; changing the opamp should make no difference. The balancing network consists of a loading resistor to ground on each output; in this respect the output characteristics diverge from a true floating output, which would be completely isolated from ground. These loading resistors are lower than the input impedance of typical balanced inputs, so if simple differential amplifiers are used with unequal input impedances, (see the section on line inputs, below) the output balance is not significantly disturbed and clipping remains symmetrical on the hot and cold outputs.
http://www.douglas-self.com/ampins/balanced/balfig6.gif
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楼主
发表于 2023-10-30 17:35
