Power amplifier bias control circuit and method
AssigneesAlps Electric Co., Ltd., QUALCOMM Incorporated
InventorsRichard K. Kornfeld, Ana L. Weiland, Mitsunari Okazaki
Life of this patent
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Abstract
A control circuit for a multi-stage power amplifier (such as in a portable radio transmitter) compensates for fluctuations in ambient temperature, load, signal level and power supply voltage, The control voltage is set by comparing a biasing level which is related to the amplifier input signal level to a voltage proportional to the power supply current of the last stage of the amplifier. The control voltage resulting from the comparison establishes the operating point of the last stage of the power amplifier.
Claims21
A power amplifier comprising:
- an FET amplifier stage having a power supply terminal and having an input terminal for receiving an externally provided variable amplitude signal and receiving a control signal at a control terminal;
- a current detector connected to said power supply terminal thereby detecting a power supply current provided to said power supply terminal of said FET amplifier stage, said current detector supplying a signal at an output terminal proportional to said power supply current;
- and
- a comparator having a first input terminal connected to a source of a reference signal and a second input terminal connected to the output terminal of said current detector, and providing in response said control signal to said amplifier stage.
A power amplifier comprising:
- an PET amplifier stage for amplifying an externally provided variable amplitude signal and having a control terminal;
- a detector for detecting a power supply current to said FET amplifier stage and providing a signal in response thereto;
- and
- a circuit for supplying a control signal to said control terminal of said FET amplifier stage, said control signal being at least partly determined by said signal provided by said detector;
- wherein said detector comprises a resistance connected between a power supply source and a power supply terminal of said FET amplifier stage.
A power amplifier comprising:
- an FET amplifier stage for amplifying an externally provided variable amplitude signal and having a control terminal;
- a detector for detecting a power supply current to said FET amplifier stage and providing a signal in response thereto;
- and
- a circuit for supplying a control signal to said control terminal of said FET amplifier stage, said control signal being at least partly determined by said signal provided by said detector;
- wherein said control signal is determined by a signal related to an amplitude of said externally provided variable amplitude signal and by said signal provided by said detector.
A method for operating an amplifier for amplifying an externally provided variable amplitude input signal to provide a stable operating point over varying operating conditions and said amplifier having at least one FET amplifier stage, the operating point of said FET amplifier stage being determined by a signal applied to a control terminal of said FET .amplifier stage, the method comprising the steps of:
- providing said FET amplifier stage as having a particular level of gain corresponding to a particular level of a power supply current to said FET amplifier stage, said particular level of gain being independent of said varying operating conditions;
- detecting a level of said power supply current to said FET amplifier stage;
- providing a voltage which is proportional to said power supply current level;
- providing a reference signal;
- comparing said reference signal to said proportional voltage and generating a signal in response;
- and
- applying the generated signal to said control terminal, wherein the generated signal causes said FET amplifier stage to operate at the stable operating point over said varying operating conditions.
A method of operating an amplifier for amplifying an externally provided variable amplitude input signal, the amplifier having at least one FET amplifier stage which amplifies said externally provided variable amplitude input signal and having an operating point set by a control signal provided thereto, and having a particular level of gain corresponding to a particular level of a power supply current to said at least one FET amplifier stage, said particular level of gain being independent of operating conditions, the method comprising the steps of:
- providing a first signal related to a level of said externally provided variable amplitude input signal;
- providing a second signal related to said gain of said at least one FET amplifier stage;
- comparing said first and second signals and generating a signal in response;
- and
- applying said generated signal to said at least one FET amplifier stage as said control signal.
A steady operating point amplifier comprising:
- an FET amplifier, having a drain terminal for receiving a supply current and for providing an output signal, and having a gate terminal coupled to receive an input signal and coupled to a control voltage;
- means for providing an indication of a level of said supply current;
- a terminal receiving a bias control signal indicating a desired operating point of said FET amplifier;
- and
- means for comparing said bias control signal to said level indication and producing said control voltage, said control voltage thereby controlling the level of said supply current;
- wherein a desired operating point of said FET amplifier is maintained constant over variations in operating conditions.
Dependencies are inferred from the claim text.