Two-step beat frequency quantizer based ADC with adaptive reference control for low swing bio-potential signals

A two-step fully digital beat frequency quantizer based continuous time ADC is demonstrated in a 65nm test chip to achieve high resolution (6-7 ENOB) for direct conversion of low swing (<;10mV) bio-potential signals. The resolution of ADC can be adaptively controlled depending on the input signal swing. A triple-sampling technique generates a synchronous ADC output from an asynchronous beat frequency quantizer. The proposed two-step ADC achieves a 44.5dB SNDR which is 5.6dB higher than the previously proposed single step architecture for a 10mVpp, 300Hz differential input signal.