AD7746 Principle: how do you measure the charge on the capacitor?

I am now using AD7746 in a medical telemetry system, the performance is really impressive. However, I do not fully understand the operation principle.

In the datasheet on Page 20, it says"A square-wave excitation signal is applied on the CX during the conversion and the modulator continuously samples the charge going through theCX."

I am wondering how to you implement a circuit to detect the charge on the sensor? Does other products such as AD7148 has the similar circuitry for capacitance detection? Is it possible to show some details of the charge sensing circuitry?I feel very interest in this part.

Thank you for your attention.