US Patent 9998131 Hybrid analog-to-digital converter

An analog-to-digital converter (ADC) circuit includes a first ADC stage comprising a first successive approximation register (SAR) circuit that is configured to convert a current analog input signal into a first digital signal corresponding to a most-significant-bits (MSB) portion of a current digital output signal, and to generate a residual voltage corresponding to a voltage value difference between the current analog input signal and the first digital signal; a second ADC stage, coupled to the first ADC stage, comprising an amplifier circuit that is configured to amplify the residual voltage; and a third ADC stage, coupled to the second ADC stage, comprising a second SAR circuit that is configured to convert the amplified residual voltage into a second digital signal corresponding to a least-significant-bits (LSB) portion of the current digital output signal when the first SAR circuit receives a subsequent analog input signal.