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Abstract

A digitally programmable Bessel filter includes a plurality of serially connected stages or biquads with each biquad including a plurality of programmable operational transconductance amplifiers. The first stage of the filter provides an all pass equal amplitude response. Two stages provide pulse slimming (first and second derivatives of an input pulse), and three stages provides a sixth order Bessel low pass function. The operational transconductance amplifiers are controlled by a fine tuning control signal, and an array of integrating capacitors are selectively controlled by a coarse tuning signal. The fine tuning and coarse tuning signals are generated in a phase locked loop from a reference clock and a reference biquad which receives the reference clock. The phase locked loop includes a phase detector responsive to the reference clock and the reference biquad, whose output is integrated.

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First Claim