Digital compensation method for Sine filters in data acquisition systems based on sigma-delta ADCs

Abstract

Modern day high resolution data acquisition systems essentially uses sigma delta converters to achieve superior performance. These data converters utilize inbuilt Sine filtering (low pass) to remove high frequency noise shaped by sigma delta modulators. Sine filters are also called cascaded integrated-comb (CIC) digital filters. Sine filters implementation does not require multiplication therefore their realization in hardware devices is convenient. Nevertheless, these filters suffer from the problem of pass band droop (non-flat pass band), which worsens with increasing order of the filter and also from stop band ripples. This paper introduces a design and implementation of equiripple FIR filter to compensate the pass band droop in Sine filter response. The design can be implemented in any simple microcontroller such as PIC microcontroller, without using the multiplier unit. Paper also presents the results of the simulated equiripple FIR on PIC microcontroller simulator environment MPLAB IDE. The stop band ripple characteristics of the compensated filter are also discussed. This kind of implementation is suitable for high resolution telemetry system which uses embedded Sigma delta converters along with microcontroller or DSP processors. sheet.