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Increased Feedback-Stabilized Amplifier

2015-01-01 02:44  
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The usual method for using a current-feedback amplifier to drive a capacitive load isolates the loa
Increased Feedback-Stabilized Amplifier

d with a resistor in series with the amplifier`s output. A better solution involves only the amplifier`s feedback resistors (Fig. 58-3(a)). Because the feedback resistors determine the amplifier`s compensation, you can select the optimal value for these feedback resistors for almost any capacitive load. Feedback resistance RF sets the amplifier`s bandwidth. Increasing RF reduces the amplifier`s bandwidth, which significantly improves the amplifier`s ability to drive capacitive loads. Feedback resistor RG sets the amplifier`s gain. You cannot get the data necessary to calculate alternate values for RF from most data sheets. However, a few minutes at the bench with a network analyzer will generate the data to make a graph of the value of the feedback resistor vs. the amount of capacitive load the amplifier can drive (Fig. 58-3(b)). Start with the recommended data-sheet value for feedback resistor RF and measure the amplifier`s frequency response without any capacitive load. Note the bandwidth, then add capacitive loading until the response peaks by about 5 dB. Record this value of capacitance; it is the maximum amount for that feedback resistor. Then, increase the value of the feedback resistor and repeat the procedure until you develop a graph like the one in diagram.



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