CM Charge Pumping
Stable and Simple
Circuit Structure and Operation
- CM signal sensed at the input of the front-end LNA
- If the CM signal exceeds the desired CM range, the displacement current from the CM input absorbed by a CMCP
- Input swing kept within the desired CM range, even in the presence of excessively large CM interferences going beyond supply rails
Block Diagram
Pros
No stability issue caused by the variation of electrode impedances
No additional electrode for VDRL application or VCM sensing required
- VIN,CM itself suppressed
Input CM range (or input swing) requirement relaxed
Input CM range extended beyond supply rails
Cons
CMRR still limited by circuit and electrode mismatches and not improved much
Significant power overhead caused by the CMCP
Input-referred noise of the front-end LNA increased due to the contribution from CMCP
Suffers from a trade-off between the input CM range improvement and input-referred noise degradation
Linearity of the recording circuit degraded due to the intermodulation between the CM and DM signals à Can be mitigated at the cost of higher power consumption