The device includes a 20-bit output
resolution mode which can be used for high order decimation (such as: 64x, 128x) to
avoid SNR degradation due to quantization noise limitation. In this mode, no additional
JESD204B output lanes are added but the output data is transmitted at 2x the output rate
and two consecutive 16-bit samples are filled with one 20-bit sample. So for example, a
single band complex decimation would go from LMFS = 4841 (16-bit output mode) to LMFS =
48
81 (20-bit output mode) as illustrated in
Table 6-18.
The 20-bit output
mode is enabled by setting D7 in 0x2C (DIGITAL page) and selecting viable decimation
and LMFS mode.
Table 6-18 JESD Frame Assembly Comparison between 16-bit and 20-bit Output ModeLMFS = 4841 | | LMFS = 4881 |
---|
xI0[15:8] | xI0[7:0] | xQ0[15:8] | xQ0[7:0] | | xI0[31:24] | xI0[23:16] | xI0[15:8] | xI0[7:0] | xQ0[31:24] | xQ0[23:16] | xQ0[15:8] | xQ0[7:0] |
| | | | | 20-bit sample I | 0000 00000000 | 20-bit sample Q | 0000 00000000 |