Efficient microphone bias amplifier with high output voltage/current capability and excellent PSRR

An output stage for an amplifier circuit, comprising:

• a first transistor;
• a feedback loop comprising an amplifier coupled to said first transistor;
• a second transistor coupled to said amplifier and to said first transistor;
• a current source conducting through said second transistor;
• a third transistor coupled to a voltage source providing a source current;
• said amplifier driving said third transistor and the third transistor provides said source current to said first transistor and to an output of said output stage;
• and
• said feedback loop is adapted to control the current conducted through said first transistor such that the current conducted by the first transistor is equal to the current conducted by the second transistor.

An output stage for an amplifier circuit, comprising:

• a first transistor;
• and
• a feedback loop comprising an amplifier coupled to said first transistor;
• a second transistor coupled to said amplifier and to said first transistor;
• a current source conducting through said second transistor;
• a third transistor coupled to a voltage source providing a source current;
• said amplifier driving said third transistor and the third transistor provides said source current to said first transistor and to an output of said output stage;
• and
• said amplifier comprises a negative input terminal, a positive input terminal and an output terminal, said first transistor comprises a gate, source and drain, said second transistor comprises a gate, source and drain, said third transistor comprises a gate, source and drain, wherein said first and second transistor drains are coupled to a return voltage, said first and second transistor gates are coupled together, said second transistor source is coupled to said current source and said amplifier negative input terminal, said first transistor source is coupled to said amplifier positive input terminal and said third transistor drain, said amplifier output terminal is coupled to said third transistor gate, and said third transistor source is coupled to said voltage source.

An output stage for an amplifier circuit, comprising:

• a first transistor;
• a feedback loop comprising an amplifier coupled to said first transistor;
• a second transistor coupled to said amplifier and to said first transistor;
• a current source conducting through said second transistor;
• a third transistor coupled to a voltage source providing a source current;
• said amplifier driving said third transistor and the third transistor provides said source current to said first transistor and to an output of said output stage;
• and
• said amplifier comprises a negative input terminal, a positive input terminal and an output terminal, said first transistor comprises a gate, source and drain, said second transistor comprises a gate, source and drain, said third transistor comprises a gate, source and drain, wherein said first and second transistor drains are coupled to a return voltage, said first and second transistor gates are coupled together, said second transistor source is coupled to said current source and said amplifier negative input terminal, said first transistor source is coupled to said amplifier positive input terminal and said third transistor drain, said amplifier output terminal is coupled to said third transistor gate, and said third transistor source is coupled to said voltage source and an output voltage is generated at said first transistor source.

A microphone bias amplifier circuit, comprising:

• an input stage having an input node;
• an output stage-coupled to said input stage and providing an output voltage, said output stage comprising a first transistor coupled to a first feedback loop;
• said first feedback loop comprising a first amplifier coupled to said first transistor;
• a second transistor coupled to said first amplifier and to said first transistor;
• a current source conducting through said second transistor;
• a third transistor coupled to a voltage source providing a source current;
• said first amplifier driving said third transistor, and the third transistor provides said source current to said first transistor and to an output of said output stage;
• and
• said first feedback loop is adapted to control the current conducted through said first transistor such that the current conducted by the first transistor is equal to the current conducted by the second transistor.

A microphone bias amplifier circuit, comprising:

• an input stage having an input node;
• an output stage coupled to said input stage and providing an output voltage, said output stage comprising a first transistor coupled to a first feedback loop;
• said first feedback loop comprising a first amplifier coupled to said first transistor;
• a second transistor coupled to said first amplifier and to said first transistor;
• a current source conducting through said second transistor;
• a third transistor coupled to a voltage source providing a source current;
• said first amplifier driving said third transistor, and the third transistor provides said source current to said first transistor and to an output of said output stage;
• said first feedback loop is adapted to control the current conducted through said first transistor, and
• said input stage is adapted to receive an input voltage from said input stage, wherein said first transistor comprises a gate, source and drain, wherein said third transistor comprises a gate, source and drain, wherein said output voltage is generated at said first transistor source, wherein said output voltage is substantially equal to said input voltage.

A microphone bias amplifier circuit, comprising:

• an input stage having an input node;
• an output stage coupled to said input stage and providing an output voltage;
• said output stage comprising a first transistor coupled to a first feedback loop;
• said first feedback loop comprising a first amplifier coupled to said first transistor;
• a second transistor coupled to said first amplifier and to said first transistor;
• a current source conducting through said second transistor;
• a third transistor coupled to a voltage source providing a source current;
• said first amplifier driving said third transistor, and the third transistor provides said source current to said first transistor and to an output of said output stage;
• said first feedback loop is adapted to control the current conducted through said first transistor, and
• said input stage comprises a second amplifier, and said second amplifier drives said first and second transistors.

A microphone bias amplifier circuit, comprising:

• an input stage having an input node;
• an output stage coupled to said input stage and providing an output voltage;
• said output stage comprising a first transistor coupled to a first feedback loop;
• said first feedback loop comprising a first amplifier coupled to said first transistor;
• a second transistor coupled to said first amplifier and to said first transistor;
• a current source conducting through said second transistor;
• a third transistor coupled to a voltage source providing a source current;
• said first amplifier driving said third transistor, and the third transistor provides said source current to said first transistor and to an output of said output stage;
• said first feedback loop is adapted to control the current conducted through said first transistor,
• said input stage comprises a second amplifier, and said second amplifier drives said first and second transistors;
• and
• a global feedback loop coupled between said output voltage and said input stage input node.

A microphone bias amplifier circuit, comprising:

• an input stage having an input node;
• and
• an output stage coupled to said input stage and providing an output voltage, said output stage comprising a first transistor coupled to a first feedback loop, said first feedback loop comprising a first amplifier coupled to said first transistor, a second transistor coupled to said first amplifier, a current source conducting through said second transistor, a third transistor coupled to a voltage source providing a source current, said first amplifier driving said third transistor, said first and second transistors being coupled together, wherein the third transistor provides said source current to said first transistor and to an output of said output stage;
• a global feedback loop coupled between said output voltage and said input stage input node;
• and
• said global feedback loop further comprises a first resistor, and a second resistor coupled between said second amplifier and ground.

A method of biasing a microphone with an amplifier circuit having an output and including an input stage coupled to an output stage, said output stage having a feedback loop coupled to a first transistor in said output stage,and said feedback loop includes an amplifier coupled to said first transistor, a first current source conducting through a second transistor and coupled to said amplifier, said amplifier driving a third transistor conducting a source current from a voltage source, said first and second transistors being coupled together, and said input stage is adapted to receive an input voltage, wherein said first transistor and third transistors each include a gate, source and drain, said method comprises the steps of:

• controlling a current conducted through said first transistor with said output stage feedback loop;
• providing the source current from said third transistor to the first transistor and to said amplifier circuit output;
• and
• generating an output voltage at said first transistor source and said amplifier circuit output, wherein said output voltage is substantially equal to said input voltage.

A method of biasing a microphone with an amplifier circuit having an output and including an input stage coupled to an output stage, said output stage having a feedback loop coupled to a first transistor in said output stage, and said feedback loop comprises an amplifier coupled to said first transistor, a first current source conducting through a second transistor and coupled to said amplifier, said amplifier driving a third transistor conducting a source current from a voltage source, said first and second transistors being coupled together, and said input stage is adapted to receive an input voltage, wherein said first and third transistors each comprise a gate, source and drain, and the source current conducted through said first transistor equals the current conducted through said second transistor, said method comprising the steps of:

• controlling a current conducted through said first transistor with said output stage feedback loop;
• providing the source current from said third transistor to the first transistor and to said amplifier circuit output;
• and
• generating an output voltage at said first transistor source and said amplifier circuit output, wherein said output voltage is substantially equal to said input voltage.