Controlling the bandwidth of an analog filter

In a wireless device, a method for obtaining a desired bandwidth for an analog filter, the analog filter having an input, an output, a bandwidth-determining component and a quality factor, comprising the steps of:

• a) predetermining a difference between an amplitude of a magnitude response of the analog filter at a first frequency and another amplitude of the magnitude response of the analog filter at a second higher frequency, based on ideal responses of the analog filter at each of said frequencies calculated from design of the analog filter;
• b) increasing the quality factor of the analog filter from a normal Q to a high Q to produce a peak response at a peaking frequency between the first frequency and the second frequency;
• c) sequentially setting a value of the bandwidth-determining component to one of a plurality of values, and, while the bandwidth-determining component is set to each value:
• c1) concurrently applying to the input of the analog filter a first input signal at the first frequency and a second input signal at the second frequency, thereby producing a magnitude response at the output of the analog filter, and
• c2) calculating a difference between an amplitude of the magnitude response at the first frequency and another amplitude of the magnitude response at the second frequency;
• d) comparing each of a plurality of differences calculated in step c to the predetermined difference to obtain a plurality of errors, wherein each error represents a numerical separation between each difference calculated in step c and the predetermined difference for a same value of the bandwidth-determining component;
• e) based upon the plurality of errors, selecting one value from the plurality of values as an optimal value for the bandwidth-determining component, the selected one value being a value of the bandwidth-determining component associated with a smallest error;
• and
• f) setting the value of the bandwidth-determining component to the selected one value, to obtain the desired bandwidth for the analog filter when the quality factor is at the normal Q.