Variable supply biasing method and apparatus for an amplifier

An integrated circuit having a supply voltage input, said integrated circuit comprising:

• an amplifier;
• a biasing circuit including:
• a reference voltage circuit having a reference voltage output, said reference voltage circuit to generate a substantially fixed reference voltage at said reference voltage output;
• a comparator coupled to said supply voltage input and to said reference voltage output;
• a first current source coupled to said amplifier, said first current source for biasing said amplifier with a first substantially fixed current when said supply voltage input is within a first predetermined voltage range;
• and
• a second current source coupled to said amplifier and responsive to said comparator, said first and said second current sources for biasing said amplifier with a second substantially fixed current when said supply voltage input is within a second predetermined voltage range.

An electronic device comprising:

• an electronic circuit including:
• an amplifier;
• and
• a biasing circuit coupled to said amplifier, said biasing circuit to bias said amplifier with a first operating current over a first predetermined voltage range corresponding to a first supply voltage, said biasing circuit to bias said amplifier with a second operating current over a second predetermined voltage range corresponding to a second supply voltage, the first and the second operating currents remaining substantially fixed over the first and the second predetermined voltage ranges, respectively.

A method of biasing an amplifier, the amplifier operable at a supply voltage including a first supply voltage and a second supply voltage, the method comprising the steps of:

• generating a reference voltage that is substantially fixed over the first and the second supply voltages;
• comparing the reference voltage and a voltage proportional to the supply voltage;
• detecting, in response to the step of comparing, a first predetermined voltage range corresponding to the first supply voltage;
• detecting, in response to the step of comparing, a second predetermined voltage range corresponding to the second supply voltage;
• in response to the step of detecting the first predetermined voltage range, biasing the amplifier with a first current that remains substantially fixed over the first predetermined voltage range;
• and
• in response to the step of detecting the second predetermined voltage range, biasing the amplifier with a second current that remains substantially fixed over the second predetermined voltage range.

A communication system comprising:

• a base station;
• a mobile station including:
• an electronic circuit including:
• an amplifier;
• and
• a biasing circuit coupled to said amplifier, said biasing circuit to operate said amplifier at a first current when a supply voltage of said electronic circuit is within a first predetermined voltage range corresponding to a first supply voltage, said biasing circuit to operate said amplifier at a second current when the supply voltage is within a second predetermined voltage range corresponding to a second supply voltage, the first and the second currents remaining substantially fixed over the first and the second predetermined voltage ranges, respectively.

A portable electronic device, comprising:

• electronic circuitry to operate at one of a first supply voltage and a second supply voltage;
• an integrated circuit having a supply voltage input, said integrated circuit including:
• an amplifier;
• and
• a biasing circuit coupled to said amplifier, said biasing circuit to bias said amplifier with a first substantially fixed current in response to the supply voltage input being biased within a first predetermined voltage range corresponding to the first supply voltage, said biasing circuit to bias said amplifier with a second substantially fixed current in response to the supply voltage input being biased within a second predetermined voltage range corresponding to the second supply voltage.

An electronic circuit having a supply voltage input, said electronic circuit capable of operating at a first supply voltage and a second supply voltage, the second supply voltage being less than the first supply voltage, said electronic circuit comprising:

• an amplifier;
• a biasing circuit including:
• a detector to detect a first predetermined voltage range corresponding to the first supply voltage and a second predetermined voltage range corresponding to the second supply voltage;
• and
• a variable current source coupled to and responsive to said detector, said variable current source to bias said amplifier with a first current over the first predetermined voltage range, said variable current source to bias said amplifier with a second current that is less than the first current over the second predetermined voltage range, the first and the second currents being substantially fixed over the first and the second predetermined voltage ranges, respectively.