SBASB89 May 2025 ADS117L14 , ADS117L18
PRODUCTION DATA
Figure 9-1 shows an input anti-alias filter using the THS4551 fully-differential input signal driver. The goal of this design is an anti-alias filter at the ADC input to attenuate out-of-band signals at the modulator sample rate (fMOD). The filter requirement is 90dB attenuation at the fMOD frequency (12.8MHz in high-speed mode) using OSR = 32 (fDATA = 400kHz) in wideband filter mode. The other filter design goals are flat amplitude response and low group delay error within the pass band of the signal.
Table 9-1 lists the target design values and the actual values achieved in this design.
| FILTER PARAMETER | TARGET VALUE | ACTUAL VALUE |
|---|---|---|
| Voltage gain | 0dB | 0dB |
| Alias rejection at 12.8MHz | 90dB | 90dB |
| –0.1dB frequency | 250kHz | 260kHz |
| –3dB frequency | 500kHz | 550kHz |
| Pass-band amplitude peaking | 20mdB | 12mdB |
| Group delay linearity | 0.1μs | 0.017μs |
| Total noise of the filter and ADC (165kHz bandwidth) | 12μV | 11.8μV |