Capacitance_multiplier

Published:2009/7/25 5:35:00 Author:Jessie | From:SeekIC

Figure 9-37 shows a DAC0830 connected as a capacitance multiplier，Actually， thecircuit is a DAC－controlled amplifier (used for capacitance multiplication) to give microprocessor control of system time-domain or frequency-domain response. The microprocessor controls the digital input to the DAC、which controls the amplifier to produce a variable capacitance，The capacitance can be used to varythe time constant of RC circuits varying either time or frequency．In this circuit the DAC adjusts the gam of a stage with fixed capacitive feedback. This produces aMiller-effect equivalent input capacitance equal to the fixed capacitance multiplied by 1 plus the amplifier gain．The voltage across the equivalent input capacitance to ground is limited to the maximum output voltage of op amp A1, divided by 1 plus 2n/D, where:n = the DAC bits of resolution, and D = decimal equivalent of the binary input. NATIONAL SEMICONDUCTOR, APPLICATION NOTE 271, P. 667.



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