The ADC32RF8x can be used in dc-coupling applications. However, the following points must be considered when designing the system:

1. Ensure that the correct common-mode voltage is used at the ADC analog inputs.

   The analog inputs are internally self-biased to V_CM through approximately a 33-Ω resistor. The internal biasing resistors also function as a termination resistor. However, if a different termination is required, the external resistor R_TERM can be differentially placed between the analog inputs, as shown in Figure 9-5. The amplifier V_OCM pin is recommended to be driven from the CM pin of the ADC to help the amplifier output common-mode voltage track the required common-mode voltage of the ADC.

   

   Set the INCR CM IMPEDANCE bit to increase the RCM from 0 Ω to > 5000 Ω.

   R_DC is approximately 65 Ω.

   Figure 9-5 The ADC32RF8x in a DC-Coupling Application
2. Ensure that the correct SPI settings are written to the ADC.

   As shown in Figure 9-6, the ADC32RF8x has a digital block that estimates and corrects the offset mismatch among four interleaving ADC cores for a given channel.

   Figure 9-6 Offset Corrector in the ADC32RF8x

   The offset corrector block nullifies dc, f_S / 8, f_S / 4, 3 f_S / 8, and f_S / 2. The resulting spectrum becomes free from static spurs at these frequencies. The corrector continuously processes the data coming from the interleaving ADC cores and cannot distinguish if the tone at these frequencies is part of signal or if the tone originated from a mismatch among the interleaving ADC cores. Thus, in applications where the signal is present at these frequencies, the offset corrector block can be bypassed.