Methods and apparatuses for implementing variable bandwidth RF tracking filters for reconfigurable multi-standard radios

摘要

A variable bandwidth filter includes a first filter branch in parallel with a second filter branch. The first filter branch includes a first resistance in series with an input and a first output, and N parallel paths across the first output. The second filter branch includes a second resistance in series with the input and a second output, and N parallel paths across the second output. A clock tunes the first and second filter branches to a center frequency. A combiner produces a difference signal including a difference between the output of the first filter branch and the output of the second filter branch to provide a filter output having an adjustable bandwidth with reference to a center frequency. The bandwidth is adjusted by changing a value of at least one resistor or at least one capacitor in one or more of the first filter branch or the second filter branch.

主权项

1. A variable-bandwidth filter comprising:
a first filter branch in parallel with a second filter branch; the first filter branch comprising a first resistance in series with an input and a first output, and a first plurality of N parallel paths across the first output, each of respective paths of the first plurality of N parallel paths comprising a corresponding capacitor in series with a corresponding switch and a common terminal; the second filter branch comprising a second resistance in series with the input and a second output, and a second plurality of N parallel paths across the second output, each of respective paths of the second plurality of N parallel paths comprising a corresponding resistor-capacitor (RC) network in series with a corresponding switch and a common terminal; a clock tuning the first and second filter branches to a center frequency by selectively controlling with clock signals the switches of the first and second filter branches to switch at the center frequency, in which the clock signals that selectively control all the switches of the N parallel paths in the first filter branch have a same frequency and a different phase with reference to the clock signals that selectively control all the switches of the N parallel paths in the second filter branch, and in which the clock signals of the first filter branch have a first on-time duration that is different than a second on-time duration of the clock signals of the second filter branch; a combiner for producing a difference signal comprising a difference between the first output of the first filter branch and the second output of the second filter branch; and the difference signal providing a filter output for the variable bandwidth filter wherein the filter bandwidth is adjusted with reference to a center frequency, the filter bandwidth being adjusted by changing a value of at least one resistor or at least one capacitor in one or more of the first filter branch or the second filter branch.