Method and circuit for controlling quiescent current of amplifier

A circuit for controlling a quiescent current of an amplifier, the amplifier including a preamplifier, error amplifiers coupled to the preamplifier, and output devices driven by the error amplifiers, the error amplifiers having an input-referred offset voltage, said circuit comprising:

• a correction voltage generator coupled to an input of the error amplifiers, said correction voltage generator supplying a correction voltage to the input;
• a quiescent current detector coupled to an output of the error amplifiers, said quiescent current detector detecting a quiescent current flowing through the output devices;
• a calibration circuit coupled to said quiescent current detector and to said correction voltage generator, said calibration circuit adjusting the correction voltage so that the quiescent current is calibrated to a predetermined current value;
• and
• a switching circuit coupled between said preamplifier and a signal input port, said switching circuit electrically disconnecting differential inputs of said preamplifier from the signal input port and electrically connecting the differential inputs when said quiescent current detector and said calibration circuit are operating.

An amplifier circuit having a controlled quiescent current, said amplifier circuit comprising:

• an input port for receiving an input signal;
• an output port for outputting an output signal;
• a preamplifier coupled to said input port;
• error amplifiers coupled to said preamplifier, said error amplifiers having an input-referred offset voltage;
• output devices coupled between said error amplifiers and said output port;
• a correction voltage generator coupled to an input of said error amplifies, said correction voltage generator supplying a correction voltage to the input;
• a quiescent current detector coupled to an output of said error amplifiers, said quiescent current detector detecting a quiescent current flowing through said output devices;
• a calibration circuit coupled to said quiescent current detector and to said correction voltage generator, said calibration circuit adjusting the correction voltage so that the quiescent current is calibrated to a predetermined current value;
• and
• a switching circuit coupled between said input signal port and said preamplifier, said switching circuit electrically disconnecting differential inputs of said preamplifier from said input port and electrically connecting the differential inputs when said quiescent current detector and said calibration circuit are operating.

A amplifier circuit having a controlled quiescent current, said amplifier circuit comprising:

• an input port for receiving an input signal;
• an output port for outputting an output signal;
• a preamplifier coupled to said input port;
• a first pair of error amplifiers coupled to a first output of said preamplifier, said first pair of error amplifiers having a first input-referred offset voltage;
• first output devices coupled between said first pair of error amplifiers and said output port;
• a first correction voltage generator coupled to an input of said first pair of error amplifies, said first correction voltage generator supplying a first correction voltage to the input;
• a first quiescent current detector coupled to an output of said first pair of error amplifiers, said first quiescent current detector detecting a first quiescent current flowing through said first output devices;
• a second pair of error amplifiers coupled to a second output of said preamplifier, said second pair of error amplifiers having a second input-referred offset voltage;
• second output devices coupled between said second pair of error amplifiers and said output port;
• a second correction voltage generator coupled to an input of said second pair of error amplifies, said second correction voltage generator supplying a second correction voltage to the input of said second pair of error amplifiers;
• a second quiescent current detector coupled to an output of said second pair of error amplifiers, said second quiescent current detector detecting a second quiescent current flowing through said second output devices;
• and
• a calibration circuit coupled to said first and second quiescent current detectors and to said first and second correction voltage generators, said calibration circuit adjusting the first and second correction voltage so that the first and second quiescent currents are calibrated to a predetermined current value.

An apparatus for controlling a quiescent current of an amplifier, the amplifier including a preamplifier, error amplifiers coupled to the preamplifier, and output devices driven by the error amplifiers, the error amplifiers having an input-referred offset voltage, said apparatus comprising:

• means for applying a calibration voltage to an input of the error amplifiers;
• means for calibrating a quiescent current of the output devices by changing the calibration voltage so that the calibrated quiescent current has a predetermined current value, the calibration voltage corresponding to the calibrated quiescent current being set as a correction voltage;
• means for applying the correction voltage to the input of the error amplifier during operation of the amplifier;
• and
• means for electrically disconnecting differential inputs of the amplifier from a signal input port and short-circuiting the differential inputs during said applying and said calibrating.

A method for controlling a quiescent current of an amplifier, the amplifier including a preamplifier, error amplifiers coupled to the preamplifier, and output devices driven by the error amplifiers, the error amplifiers having an input-referred offset voltage, said method comprising:

• applying a calibration voltage to an input of the error amplifiers;
• calibrating a quiescent current of the output devices, including:
• detecting the quiescent current;
• comparing the detected quiescent current with a reference current having the predetermined current value;
• generating a control signal based on a result of said comparing;
• changing the calibration voltage in accordance with the control signal;
• repeating said detecting, comparing, generating, and changing until the quiescent current substantially equals the reference current;
• and
• setting the calibration voltage corresponding to the calibrated quiescent current as a correction voltage;
• and
• operating the amplifier with the correction voltage applied to the input of the error amplifiers.

A circuit for controlling a quiescent current of an amplifier, the amplifier including a preamplifier, error amplifiers coupled to the preamplifier, and output devices driven by the error amplifiers, the error amplifiers having an input-referred offset voltage, said circuit comprising:

• a correction voltage generator coupled to an input of the error amplifiers, said correction voltage generator supplying a correction voltage to the input;
• a quiescent current detector coupled to an output of the error amplifiers, said quiescent current detector detecting a quiescent current flowing through the output devices;
• and
• a calibration circuit including:
• a comparator having a first input and a second input, the first input being coupled to said quiescent current detector, the second input being coupled to a reference current corresponding to the predetermined current value;
• and
• a calibration engine coupled to an output of said comparator, said calibration engine generating a control signal based on the output of said comparator, the control signal being supplied to said correction voltage generator.

An amplifier circuit having a controlled quiescent current, said amplifier circuit comprising:

• an input port for receiving an input signal;
• an output port for outputting an output signal;
• a preamplifier coupled to said input port;
• error amplifiers coupled to said preamplifier, said error amplifiers having an input-referred offset voltage;
• output devices coupled between said error amplifiers and said output port;
• a correction voltage generator coupled to an input of said error amplifies, said correction voltage generator supplying a correction voltage to the input;
• a quiescent current detector coupled to an output of said error amplifiers, said quiescent current detector detecting a quiescent current flowing through said output devices;
• and
• a calibration circuit including:
• a comparator having a first input and a second input, the first input being coupled to said quiescent current detector, the second input being coupled to a reference current corresponding to the predetermined current value;
• and
• a calibration engine coupled to an output of said comparator, said calibration engine generating a control signal based on the output of said comparator, the control signal being supplied to said correction voltage generator.

An apparatus for controlling a quiescent current of an amplifier, the amplifier including a preamplifier, error amplifiers coupled to the preamplifier, and output devices driven by the error amplifiers, the error amplifiers having an input-referred offset voltage, said apparatus comprising:

• means for applying a calibration voltage to an input of the error amplifiers;
• means for calibrating a quiescent current including:
• means for detecting the quiescent current;
• means for comparing the detected quiescent current with a reference current having the predetermined current value;
• means for generating a control signal based on a result of said comparing;
• means for changing the calibration voltage in accordance with the control signal;
• means for repeating said detecting, comparing, generating, and changing until the quiescent current substantially equals the reference current;
• and
• means for setting the calibration voltage corresponding to the calibrated quiescent current as a correction voltage;
• and
• means for applying the correction voltage to the input of the error amplifier during operation of the amplifier.