| 摘要 |
A tuneable filter, for example, an antenna filter in a single chip radio receiver, comprises a frequency selective circuit (12) including passive reactive components. At least some of the reactive components (48 to 52) are arranged as a bank (46) which includes switches (53 to 57) for switching at least one of the reactive components in the bank into the frequency selective circuit. A controller controls the switching means to select the or a combination of the reactive components which provides an optimum sensitivity for an input signal at a first frequency. The switch settings required to optimise the sensitivity for other frequencies is determined by measuring the decrease in sensitivity for other switch settings, with the input signal still at the first frequency, and using stored data about the shape of the frequency response of the tuneable filter.
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