Patent ID: 7279976

Claim:
An apparatus including a differential amplifier circuit with a controlled common mode output voltage, comprising: first and second power supply electrodes to convey a power supply voltage; a bias electrode to convey a DC bias voltage; and differential amplifier circuitry including first and second circuit stages, coupled between said first and second power supply electrodes, and responsive to said power supply voltage and an AC-coupled differential input signal received via first and second input electrodes by providing a differential output signal with first and second output signal phases via first and second output electrodes, respectively, wherein said first and second input electrodes are DC-coupled to said bias electrode, said first circuit stage includes said first input electrode, said first output electrode, a first feedback electrode and first feedback circuitry DC-coupled between said first output and feedback electrodes, and said second circuit stage includes said second input electrode, said second output electrode, a second feedback electrode and second feedback circuitry DC-coupled between said second output and feedback electrodes; wherein said first and second output electrodes and said first and second feedback electrodes are maintained at a plurality of respective DC voltages each of which is substantially equal to a predetermined value related to said DC bias voltage.