Delta-sigma converter with bandpass filter for noise reduction in receivers
AssigneeGEC-Marconi Limited
InventorAndrew M. Thurston
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Abstract
Analogue signals are converted to digital data by use of a Sigma-Delta modulator including a pair of bandpass filters and a feedback loop including a digital to analogue converter. The tendency of such a circuit to instability is reduced or eliminated by making small variations in the phase of a clock controlling feedback pulses relative to a clock controlling data output pulses. As an alternative, corrections may be made to the feedback pulses by an additional feedback loop providing pulses for correcting the feedback pulses.
Claims26
Analogue-to-digital converter comprising bandpass filter means for filtering a signal derived from an analogue input signal, digitising means for producing, at sampling instants, samples at one of a discrete number of values corresponding to a signal derived from the output of the bandpass filter means, a feedback loop feeding a signal derived from the output of the digitising means to the bandpass filter means, the circuit being arranged to produce a minimum in quantisation noise in the passband of the filter means, in which there is provided means for producing a phase offset between the fedback pulses and the sampling instants of the digitising means to produce a desired response of the bandpass filter means at the sampling instants to a single fedback pulse.
Analogue-to-digital converter comprising bandpass filter means for filtering a signal derived from an analogue input signal, digitising means for producing, at sampling instants, samples at one of a discrete number of values corresponding to a signal derived from the output of the bandpass filter means, a feedback loop feeding a signal derived from the output of the digitising means to the bandpass filter means, the circuit being arranged to produce a minimum in quantisation noise in the passband of the filter means, in which there is provided an additional corrective feedback loop for feeding correction pulses delayed with respect to and derived from the output of the digitising means to the bandpass filter means in order to produce a desired response of the bandpass filter means at the sampling instants to a single fedback pulse.
Dependencies are inferred from the claim text.