| 摘要 |
PURPOSE:To obtain a buffer amplifier which does not need a phase compensation and actuates at high speed by setting the gains of second and third amplifiers in order that a second pole in total open-loop frequency characteristic becomes less than 0dB not depending on the phase compensation. CONSTITUTION:An AC amplifier 4 is a gain attenuating type amplifier consisting of a PNP type bipolar transistor Q1, and by combining a high gain wide band amplifier 5 with the gain attenuating type AC amplifier 4, it is made to actuate as an attenuator where the gain of the AC amplifier 4 in a former stage is less than 0dB like an open-loop frequency characteristic A in figure. Namely, it is supposed to be load resistance RL<feedback resistance Rf. Since the former stage of the second pole Pb becomes the gain attenuating type like the open-loop frequency characteristic B of the high gain wide band amplifier 5, the second pole Pc is less than 0dB like the total open-loop frequency characterisitc C of two-stage amplifier consisting of the AC amplifier 4 and the high gain wide band amplifier 5. As a result the phase compensation becomes needless.
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