Method and apparatus for robust biasing of bipolar and BiCMOS differential architectures

A method for biasing a bipolar transistor comprising the steps of:

• driving emitter current from a current source through a primary bipolar transistor;
• generating a bias voltage by tracking current through the current source in a current mirror circuit the current received through the current mirror circuit by a primary biasing bipolar transistor having a β which tracks the β of the primary bipolar transistor;
• tracking changes in current to the primary biasing bipolar transistor by a secondary biasing circuit comprising a secondary biasing bipolar transistor having a β which tracks the β of the primary bipolar transistor, the secondary biasing bipolar transistor receiving current from the current mirror circuit, changes in base current to the secondary biasing bipolar transistor causing changes in current to the primary biasing transistor;
• and
• applying the bias voltage through a base resistor to the base of a primary bipolar transistor.

An apparatus for biasing a bipolar transistor comprising:

• means for driving emitter current from a current source through a primary bipolar transistor;
• means for generating a bias voltage by tracking current through the current source in a current mirror circuit the current received through the current mirror circuit by a primary biasing bipolar transistor having a β which tracks the β of the primary bipolar transistor;
• means for tracking changes in current to the primary biasing bipolar transistor by a secondary biasing circuit comprising a secondary biasing bipolar transistor having a β which tracks the β of the primary bipolar transistor, the secondary biasing bipolar transistor receives current from the current mirror circuit, changes in base current to the secondary biasing bipolar transistor causing changes in current to the primary biasing transistor;
• and
• means for applying the bias voltage through a base resistor to the base of a primary bipolar transistor.

A bipolar transistor circuit comprising:

• a primary bipolar transistor;
• a base resistor through which a bias voltage is applied to the base of the primary bipolar transistor;
• a current source that drives emitter current through the primary bipolar transistor;
• and
• a base bias circuit generating the bias voltage and comprising:
• a current mirror circuit which tracks current through the current source;
• a primary biasing bipolar transistor having a β which tracks the β of the primary bipolar transistor and which receives current through the current mirror circuit to develop the bias voltage;
• and
• a bias resistor coupled between the bias voltage and the base of the primary biasing bipolar transistor, the bias resistor tracking resistance variations in the base resistor.