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Since the open loop gain of the opamp is extremely high and difficult to measure without being affected by noise the parameter associated with open loop gain is measured by another method as the large amplitude voltage gain (NULL amp method). Measurement of the frequency characteristics is carried out by supplying negative feedback with a 40dB inverting amplifier circuit in order to stabilize the DC operating point. By conducting measurements under these conditions the phase and gain of the high region near the 0dB intersection are equivalent to those in an open loop.