ZHCSPF7A march 2023 – june 2023 ADS127L21
PRODUCTION DATA
An IIR filter designed for stable operation requires the pole radius of the polynomial H(z) denominator to be on or within the unit circle (that is, the pole radius r must be ≤ 1). However, resulting from the finite resolution of the ADS127L21 IIR filter, the IIR filter can exhibit artifacts such as dead-band effects at zero signal input and rounding noise not contained in the original signal when the pole radius of H(z) is > 0.98. Figure 8-22 shows the unit circle in the z-plane and the IIR filter 0.98 pole radius.
The pole radius of the H(z) prototype filter design is computing by √a2, where a2 is the coefficient of the 1 + a1z–1 + a2z–2 polynomial in the H(z) denominator. The pole radius is reduced by decreasing the ratio of the data rate to the filter frequency. Evaluate the suitability of the prototype IIR filter design by testing the filter in the ADC.