| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the need of the supply of current of an operational amplifier at time except rise/fall time and to reduce power consumption by installing a means supplying current to the operational amplifier at output rise/fall time and a means varying impedance between the operational amplifier and an output terminal. SOLUTION: In a load reset period, an SRCc signal BIAS-S and an STB signal S3 are turned on and control signals S1 and S2 are turned off. Then, whole output terminals are shorted-circuited. Since the SRC signal BIAS-S is turned on, an operational amplifier 1 has high amplitude performance and has high through rate. In a next high speed writing period, the control signals S1 and S2 are changed to on and the STB signal S3 to off. The short-circuit of the output terminals is released. Since the control signals S1 and S2 are turned on, the load of the operational amplifier 1 drops and the SRC signal BIAS-S is turned on, output voltage changes at high speed. Impedance between the operational amplifier 1 and the output terminal can be changed to two stages by switch elements 3a and 3b, desired output can be obtained at high speed and the through rate becomes high.
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