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The data transfer speed of a microcomputer bus can be improved by adding an active circuit to the bus. This active circuit amplifies the bus voltage and feeds back to the bus a current which is proportional to the time rate of change of the bus voltage. This circuit effectively adds a negative capacitance to the bus. The practical capacitance canceling capability is limited by the propagation delay time of the operational amplifier in the active circuit. The theory of microcomputer bus structures with negative capacitance including effects of amplifier delay is presented. Typically, an operational amplifier with propagation delay less than one tenth of the bus time constant is required to achieve significant (factor of 2) bus speed improvement. High performance operational amplifiers were used to construct a working model of the negative capacitance bus terminator. The experimental results agree well with the theory.
Date of Publication: Aug 1985