SBAS745B December 2015 – January 2023 ADS54J66
PRODUCTION DATA
In this configuration, the DDC block includes a selectable N × fS / 16 complex digital mixer (N from –8 to +7) preceding the decimation-by-2 digital filter also with an IQ passband of approximately ±55 MHz (3 dB) centered at N × fS / 16. A positive value for N inverts the spectrum. In addition, a fS / 8 complex digital mixer is added after the decimation filter transforming the output back to real format and centers the output spectrum within the Nyquist zone.
In addition, the ADS54J66 supports a 0-pad feature where a sample with value = 0 is added after each sample. In this way the output data rate is interpolated to 500 MSPS (real) with a second image inverted at fS / 2 – fIN.
The stop-band attenuation is approximately 90 dB for in-band aliases from negative frequencies and approximately 55 dB for out-of-band aliases. The passband flatness is ±0.1 dB. Figure 7-9 shows the filtering operation in DDC mode 4 and 7. Table 7-5 shows corner frequencies of decimation filter in DDC mode 4 and 7. Figure 7-10 and Figure 7-11 show frequency response of the filter.
CORNERS | LOW PASS |
---|---|
–0.1 dB | 0.102 × fS |
–0.5 dB | 0.105 × fS |
–1 dB | 0.108 × fS |
–3 dB | 0.113 × fS |