SBASB89 May 2025 ADS117L14 , ADS117L18
PRODUCTION DATA
The following figures are produced by the TINA-TI™, SPICE-based analog simulation program. Download the THS4551 SPICE model at the THS4551 product folder.
Figure 9-2 shows the frequency response of the anti-alias filter and the total response of the anti-alias filter and ADC. As shown in this image, the filter provides 90dB stop-band attenuation from the Nyquist frequency to the 12.8MHz fMOD frequency.
Figure 9-3 shows the analog filter group delay. The 0.575μs group delay is small in comparison to the 85μs group delay of the ADC digital filter (34 / fDATA). The analog filter group delay linearity is 0.017μs, peaking at the edge of the 165kHz pass band.
Figure 9-3 Anti-alias Filter Group DelayFigure 9-4 shows the noise density of the anti-alias filter circuit, the noise density of the ADC, and the combined noise density of the filter and ADC. Noise density is the noise voltage per √Hz of bandwidth plotted versus frequency.
Figure 9-5 shows the total noise from the 1Hz start frequency up to the ADC final bandwidth. Below 200Hz, noise is dominated by 1 / f voltage and current noise of the THS4551 amplifier. Above 200Hz, noise is dominated by ADC noise. The integrated noise of the filter and ADC over the 165kHz bandwidth is 11.8μV, meeting the 12μV target value.