Switched-capacitor, fully-differential operational amplifier with high switching frequency

A method for controlling a fully-differential, switched-capacitor, operational amplifier having a first and a second differential input receiving respectively a first and a second differential drive voltage symmetric to a drive common-mode voltage, a first and a second output terminal, supplying respectively a first and a second differential output voltage symmetric to an output common-mode voltage, and a bias control terminal;

• comprising the steps of:
• connecting said first differential output to said first input terminal through a first feedback network, and connecting said second differential output to said second input terminal through a second feedback network;
• detecting said output common-mode voltage, and feeding said bias control terminal with a control signal correlated to said output common-mode voltage, thereby keeping said output common-mode voltage at a desired common-mode voltage;
• wherein said step of detecting comprises the step of detecting said first and second differential drive voltages at said first and second differential inputs of said operational amplifier, and in that said control signal is correlated to said common-mode drive voltage.

A fully-differential operational amplifier circuit, comprising:

• first and second input terminals;
• an operational amplifier having first and second differential inputs, first and second differential outputs, a bias control terminal, and a differential stage with a common node;
• first and second feedback networks connected respectively between the first differential output and the first input terminal, and between the second differential output and the second input terminal, and having first and second intermediate nodes connected respectively to the first and second differential inputs of the operational amplifier;
• and
• an error amplifier having a first input coupled to the common node of the differential stage, a second input coupled to a first reference voltage, and an output coupled to the bias control terminal.