Zarlink Semiconductor Limited

Philip Ching

Robertus Laurentius Van Der Valk

Gerrit Dijkstra

A resampler filter for use in an analog phase-locked loop has a charge pump and one or more switched capacitors switched by signals derived from a voltage controlled oscillator in the phase locked loop.

Analog PLL with switched capacitor resampling filter

An apparatus for detecting a dual tone alert signal in a telephone system capable of at least off hook mode operation includes a processing channel for each tone. Each channel consists of a bandsplit filter for extracting the tone of interest and attenuating the other tone; a comparator for comparing the output of said bandsplit filter with a threshold value; and an adaptive threshold generator for generating said threshold value adapted to the amplitude of the output of said bandsplit filter to reject speech and music imitations. The apparatus offers improved talkdown and talkoff immunity.

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Philip Ching