Question: What is the ClockPhase parameter in the ADC? How do I set this?
Answer: The output of a Switch Capacitor block is not a continuous signal. SC blocks have two phases of operation. Phase-1 is the charge acquisition phase when the input signal is sampled. During this phase, the output of the SC block is 0. Phase-2 is the charge transfer phase when the acquired charge is transferred to the output and the output is proportional to the ratio of input and output switch capacitor cell values. So, the output of the SC block is valid only during Phase-2. Application Note “AN2041 - Understanding Switched Capacitor Blocks” is a very good source of information on this subject.
If an ADC’s input is connected to the output of another SC Block,
say a 3 Op-Amp Instrumentation Amplifier or a Filter, the output of this source SC block is 0 during Phase-1 of the SC Block operation. The ADC which is also an SC Block samples the input signal on Phase-1. Because of this, the ADC will always see 0V at its input and will always produce an output of 0.
So, when the input of an ADC comes from an SC Block, the ClockPhase parameter of the ADC should be set to “Swapped”. Now, the ADC modulator will sample its input on Phase-2 of the SC Block cycle when the input is valid. This will produce the correct ADC result. If the input to the ADC is a continuous signal from a CT block, the Analog bus, or a direct port pin, then the ClockPhase parameter can be set to either “Normal” or “Swapped”.