Delta sigma analog-to-digital converter with increased dynamic range

Abstract

A delta sigma analog-to-digital (A/D) converter includes a digitally-controlled multiplying digital-to-analog converter (MDAC) in a feedback configuration. The MDAC is driven by a digital signal obtained from the output (or an intermediate output) of the A/D converter. An incremental feedback quantum to the first stage integrator is a function of the input values that immediately precede it. In the most general implementation, a table look-up permits an arbitrary relation between the input values and feedback quantum size. In another implementation, the A/D converter output (or intermediate output) signal drive the MDAC and the compression curve of the A/D converter bears a square-root relationship to the input analog signal; a linear relationship is restored by squaring the output signal. In a third implementation, the MDAC is driven by a digital signal obtained from the output (or an intermediate output) of the A/D converter together with an added small positive constant number. In this implementation, the compression curve starts out approximately linear and approaches a square-root relationship at the high end of the scale, while a linear relationship is restored by providing the feedback loop, in the digital domain, with the same value of signal as employed in the analog domain.