A low power high precision mixed signal analog to digital converter is provided for processing biometric signals in the presence of a large interferer signal for cableless patient monitoring； a capacitive difference circuit produces an analog difference signal by differencing an analog feedback loop signal and an input signal； an analog-to-digital converter sigma delta converter produces a digital version of the difference signal, a digital feedback loop includes a digital integrator and a capacitive digital-to-analog converter configured to produce the analog loop feedback signal based upon the digital version of the difference.
