Dithered analog-to-digital converter
AssigneeHewlett-Packard Company
InventorManfred U. Bartz
Life of this patent
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Abstract
A dithered analog-to-digital converter includes a correlator to detect dither residue in the output signal. The correlator output is accumulated and used in a feedback loop to control the gain of the dither signal so as to null the residue. Problems associated with the low bandwidth of the feedback loop, and corruption of the accumulator value due to overload, are addressed by provision of a preload register from which the accumulator is initialized on power-up and on detection of an overload. This approach provides quick settling time and avoids statistical anomalies associated with decimation approaches to overload.
Claims16
An analog to digital conversion circuit comprising:
- an input for receiving an analog input signal;
- dither circuitry for producing corresponding analog and digital dither signals;
- an analog summation circuit connected to the dither circuitry and the input for adding the analog dither signal and the analog input signal to produce a summed signal;
- at least one analog-to-digital converter having an input coupled to the analog summation circuit and having an output providing a digital output stream;
- a subtraction circuit coupled to the converter output for subtracting the digital dither from the digital output stream to provide an output signal;
- an accumulator;
- a memory for storing a non-zero initialization value that can be selectably loaded into the accumulator;
- a correlator coupled to the dither source and the subtraction circuit for generating a correlation signal related to dither residue detected in the output signal, the correlator having an output coupled to the accumulator;
- and
- gain control circuitry for controlling the gain of a circuit through which at least one of the dither signals pass responsive to data accumulated in the accumulator.
In an analog-to-digital converter having means for adding a dither signal prior to conversion, and means for removing the dither signal after conversion, an improvement comprising a correlation accumulator and a memory cooperating to initialize a gain of the dither signal to a preestablished value.
In a method of converting an input analog signal to an output digital signal, the method including adding and subsequently removing a dither signal to improve conversion accuracy, an improvement comprising:
- initializing an accumulator with a non-zero initial datum;
- correlating the output digital signal with the dither signal to produce a correlation signal;
- accumulating the correlation signal with the initial datum in the accumulator;
- and
- controlling the gain of a circuit stage through which the dither signal passes in response to the:
- data accumulated in the accumulator.
Dependencies are inferred from the claim text.