| 摘要 |
A preamplifier circuit is provided in which the feedback resistance is controllably variable according to the output signal. In particular, when the output is saturated, the resistance is decreased to a smaller value by adding a parallel resistor to the feedback resistance to lower the output to below the saturation, but the resistance remains at a larger value if the output is not too large so as to keep a high signal-to-noise (SN). In a preferred embodiment, the feedback resistance can be altered such that the output always reaches a predetermined maximum value.
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