US 4,612,533 AGranted

Harmonic distortion reduction technique for data acquistion

AssigneeThe United States of America as represented by the Secretary of the Air Force

InventorWilliam P. Evans

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Abstract

An analog to digital converter (ADC) is presented which uses a calibration technique to reduce harmonic distortion in data acquisition systems. This mechanization also allows faster conversion rates than previously possible for high resolution analog-to-digital converters. This converter makes use of a subrange or "half Flash" architecture where the subrange digital-to-analog converter (DAC) is augmented with a software calibrated DAC which removes system nonlinearities. The advantage of this system is that it allows the building of higher speed data acquisition systems with higher spurious free dynamic range than would be possible with conventional techniques. By adding the correction to the input of the subrange ADC, correction resolution can be a fraction of a quanta. A second approach using the same mathematics places at the output of the ADC a RAM or ROM look up table which linearizes the transfer function.

Claims7

Dependent claims

A self-calibrating analog-to-digital converter which receives an analog input signal and outputs a digital signal while reducing harmonic distortion, said self-calibrating analog-to-digital converter comprising:

a sample and hold circuit, which conducts analog signals;
a main range encoder, which produces a digital word signal (N.sub.1) by quantizing analog signals received from said sample and hold circuit;
a subrange digital-to-analog converter which produces an output signal by receiving and converting into analog, said digital word signal from said main range encoder;
a digital calibration means, which receives the digital word signal (N.sub.1) produced by said main range encoder, said digital calibration means outputting a digital harmonic distortion signal by extracting the harmonic distortion from the digital word signal (N.sub.1) signal produced by said main range encoder;
a calibration digital-to-analog converter which produces an analog correction signal by receiving and converting to analog said digital harmonic distortion signal from said digital calibration means;
a differencing means which produces a corrected composite signal by subtracting said output signal received from said subrange digital-to-analog converter and said analog correction signal received from said calibration digital-to-analog converter, from analog signals received from said sample and hold circuit;
a subrange encoder which produces a calibrated output byte signal (N.sub.2) by quantizing said corrected composite signal received from said differencing means;
and
a digital adding means which outputs said digital signal of said self-calibrating analog-to-digital converter by adding the digital word signal (N.sub.1), received from said main range encoder, with said calibrated output byte signal (N.sub.2), received from said subrange encoder.

6 more elements

Dependencies are inferred from the claim text.