SBAS706D April 2015 – April 2019 ADS54J60
PRODUCTION DATA.
The ADS54J60 employs eight dc offset correction blocks (four per channel, one per interleaving core). Figure 142 shows a dc correction block diagram.
The purpose of the dc offset correction block is to correct the dc offset of interleaving cores that mainly arise from the amplifier in the first pipeline stage. Any mismatch in dc offset among interleaving cores results in spurs at fS / 4 and fS / 2. The dc offset correction blocks estimate and correct the dc offset of an individual core, to the ideal mid-code value, and thereby remove the effect of offset mismatch.
The dc offset correction block can correct the dc offset of an individual core up to ±1024 codes.
In applications involving dc-coupling between the ADC and the driver, the dc offset correction block can either be bypassed or frozen because the block cannot distinguish the external dc signal from the internal dc offset. Figure 143 shows that when bypassed, the internal dc mismatch appears at dc, fS / 4, and fS / 2 frequency points and can be as big as –40 dBFS.