Patent ID: 8456337

Claim:
A system to interface an analog-to-digital converter (ADC) to inputs with arbitrary common-modes, comprising: a common-mode voltage amplifier circuit, including: a first capacitor having a first terminal that receives a first analog input signal by way of a first switch and a second terminal that receives an amplifier output voltage by way of a second switch; a second capacitor having a first terminal that receives a second analog input signal by way of a third switch, and a second terminal that receives the amplifier output voltage by way of a fourth switch; and a first operational amplifier having a positive terminal that receives a common-mode voltage, a negative terminal connected to the second terminal of the first and second capacitors by way of fifth and sixth switches, respectively, and an output terminal for providing the amplifier output voltage based on the first and second analog input signals, wherein the output terminal is connected to the negative terminal by way of a seventh switch and to the first terminal of the first and second capacitors by way of eighth and ninth switches, respectively, wherein the amplifier output voltage is equal to the common-mode voltage in first and third operating phases, and to the arbitrary common-modes in a second operating phase; and a programmable gain amplifier (PGA) circuit having a first input terminal connected to the output terminal of the first operational amplifier and a second input terminal that receives the first and second analog input signals, wherein the PGA circuit eliminates the arbitrary common-modes from the first and second analog input signals to generate first and second analog output signals that are differential about the common-mode voltage.