Digitally programmable active-RC filter
AssigneesKind Fahd University of Petroleum and Minerals, King Abdulaziz City Science and Technology
InventorHussain Alzaher
Life of this patent
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Abstract
The digitally programmable active-RC filter provides an active-RC filter having programmable time constants. An inherently linear current division network (CDN) provides the programmable time constants while preserving a high linearity property of the active-RC filter. Using this approach, wide tuning characteristics are achieved. The programmable active-RC filter uses two op-amps per integrator. Cross-coupling two of the units configured with I and Q inputs provides the reconfigurable filter with a complex bandpass and normal lowpass response. One embodiment is formed as a fourth-order filter fabricated in a standard 0.18 μm CMOS process. The complex and lowpass filters achieve in-band spurious-free dynamic ranges (SFDRs) of about 70 dB and 71 dB for bandwidths of 1 MHz and 5.5 MHz, respectively.
Claims5
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.
Dependencies are inferred from the claim text.