Stability and enhanced gain of amplifiers using inductive coupling
AssigneeConexant Systems, Inc.
InventorJames Burr Hecht
Life of this patent
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Abstract
The present invention improves the stability and enhances the gain of amplifiers, particularly transistor amplifiers, by using mutual inductive coupling to partially cancel feedback current. Inductors at the input and output of an amplifier are positioned so that a mutual inductance is created between the two inductors. The mutual inductance is used to cancel the inherent capacitive feedback of transistor amplifiers. The use of mutually coupled inductors allows a large value of effective inductance to be obtained by using relatively small inductors. The use of mutually coupled inductors also avoids the problem of low-frequency instability.
Claims39
An amplifier wherein capacitive feedback is neutralized without adding elements, the amplifier comprising:
- a transistor having an input terminal and an output terminal, wherein inherent capacitance exits between the input terminal and the output terminal to generate the capacitive feedback;
- a first inductor coupled to the input terminal of the transistor, wherein value of the first inductor is selected to provide a desired input impedance of the amplifier;
- and
- a second inductor coupled to the output terminal of the transistor, wherein value of the second inductor is selected to provide a desired output impedance of the amplifier and wherein the first inductor and the second inductor are positioned near each other to create mutual inductance between the output terminal and the input terminal to neutralize the capacitive feedback.
An apparatus wherein capacitive feedback is neutralized without adding components, the apparatus comprising:
- an amplifier having an input terminal and an output terminal, wherein inherent feedback capacitance between the input terminal and the output terminal generates the capacitive feedback;
- a first inductor coupled to the input terminal of the amplifier, wherein the first inductor is selected to provide a desired input impedance of the amplifier;
- and
- a second inductor coupled to the output terminal of the amplifier, wherein the second inductor is selected to provide a desired output impedance of the amplifier and wherein the first inductor and the second inductor are positioned relative to each other to create a mutual inductance which cancels at least a portion of the capacitive feedback in the amplifier.
A method of reducing feedback in an amplifier without adding components, the method comprising the acts of:
- coupling a first inductor to an input terminal of the amplifier, wherein the first inductor tunes input of the amplifier;
- coupling a second inductor to an output terminal of the amplifier, wherein the second inductor tunes output of the amplifier;
- and
- positioning the first inductor and the second inductor relative to each other to create a mutual inductance which cancels at least a portion of the feedback between the input terminal and the output terminal of the amplifier.
An apparatus to neutralize capacitive feedback without adding components, said apparatus comprising:
- amplifying means having an input and an output;
- first inductive means coupled to the input of the amplifying means, wherein the first inductive means tune the input of the amplifying means;
- and
- second inductive means coupled to the output of the amplifying means, wherein the second inductive means tune the output of the amplifying means and wherein the first inductive means and the second inductive means are positioned relative to each other to create a mutual inductance between the output of the amplifying means and the input of the amplifying means, the mutual inductance neutralizing the amplifying means.
An amplifier wherein capacitive feedback is neutralized without adding components, the amplifier comprising:
- a transistor having an input terminal and an output terminal, wherein an inherent capacitance exits between the input terminal and the output terminal to generate the capacitive feedback;
- a first inductor coupled to the input terminal of the transistor;
- and
- a second inductor coupled to the output terminal of the transistor, wherein the first inductor and the second inductor facilitate biasing of the transistor and wherein the first inductor and the second inductor are positioned near each other to create mutual inductance between the output terminal and the input terminal to neutralize the capacitive feedback.
A method of neutralizing feedback in an amplifier without adding components comprising the acts of:
- coupling a first inductor to an input of the amplifier;
- coupling a second inductor to an output of the amplifier, wherein the first inductor in combination with the second inductor bias the amplifier;
- and
- placing the first inductor near the second inductor to create mutual inductance, wherein the mutual inductance neutralizes feedback between the input and the output of the amplifier.
An apparatus to neutralize capacitive feedback without adding components, said apparatus comprising:
- amplifying means having an input and an output;
- first inductive means coupled to the input of the amplifying means;
- and
- second inductive means coupled to the output of the amplifying means wherein the first and the second inductive means provide biasing for the amplifying means, and wherein the first and the second inductive means are placed close to each other to create a mutual inductance to neutralize capacitive feedback between the input and the output of the amplifying means.
Dependencies are inferred from the claim text.