Programmable Capacitance Multiplier with DAC

Capacitance multiplier simulate high capacitance capacitor for analog signal signal processing. By using DAC (Digital-to-Analog Converter), we can simulate variable capacitance with very wide range, which can be used in digitally controlled analog processor (programmable filters for example). The following circuit shows a DAC0830 connected as a capacitance multiplier. This circuit is a DAC controlled amplifier (used capacitance multiplication) to give microprocessor control of system time domain or frequency domain response. Here is the schematic diagram of the circuit:

The digital input is controlled to the DAC by microprocessor, which controls the amplifier to rpoduce a variable capacitance. We can use the capacitance to vary the time constant of RC circuits varying either time or frequency. The DAC adjust the capacitance multiplied by 1 plus the amplifier gain in this circuit. 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.