Patent ID: 8508291
Filing Date: 2013-08-13
Classification: H03H

Abstract:
1. A digitally programmable active-RC filter, comprising at least one dual op-amp integrator having: a first differential op-amp having a first differential op-amp inverting input, a first differential op-amp non-inverting input, and a first differential op-amp differential output; a first resistor having a first lead connected to the first differential op-amp inverting input; a second resistor having a first lead connected to the first differential op-amp non-inverting input, the first and second resistors having second leads adapted for accepting a first differential input voltage; a second differential op-amp having a second differential op-amp inverting input, a second differential op-amp non-inverting input, and a second differential op-amp differential output; a first capacitor connected between the second differential op-amp inverting input and a positive portion of the second differential op-amp differential output; a first feedback resistor connected between the positive portion of the second differential op-amp differential output and the non-inverting input of the first differential operational amplifier; a second capacitor connected between the second differential op-amp non-inverting input and a negative portion of the second differential op-amp differential output; a second feedback resistor connected between the negative portion of the second differential op-amp differential output and the inverting input of the first differential operational amplifier; a first CDN having a current input, a first current output, a second current output, and a digital control input, the current input of the first CDN being connected to a positive portion of the first differential op-amp output, the first current output of the first CDN being connected to the second differential op-amp inverting input, the second current output of the first CDN being connected to the first differential op-amp inverting input; a second CDN having a current input, a first current output, a second current output, and a digital control input, the current input of the second CDN being connected to a negative portion of the first differential op-amp differential output, the first current output of the second CDN being connected to the second differential op-amp non-inverting input, the second current output of the second CDN being connected to the first differential op-amp non-inverting input; and wherein binary digital control words applied to the digital control inputs of the first and second CDNs adjust frequency response characteristics of the digitally programmable active-RC filter.