Circuit technique for cancelling non-linear capacitor-induced harmonic distortion
First Claim
1. A method for reducing harmonic distortion in an amplifier including a first transistor having a first non-linear collector-to-substrate capacitance, the method comprising the steps of:
- (a) applying a small signal input voltage to a first conductor coupled to a base of the first transistor and to the base of a second transistor, the second transistor having a second non-linear collector-to-substrate capacitance;
(b) producing a first variation in a collector voltage of the first transistor and a second variation in a collector voltage of the second transistor in response to the input voltage, and producing a first non-linear current in the first non-linear collector-to-substrate capacitance in response to the first variation and a second non-linear current in the second non-linear collector-to-substrate capacitance in response to the second variation;
(c) causing the first non-linear current to flow in a second conductor connected to the collector of the first transistor;
(d) causing the second non-linear current to flow in a control conductor of a current mirror, and operating the current mirror to produce a correction current in an output conductor of the current mirror in response to the second non-linear current;
(e) causing the correction current to also flow in the second conductor and thereby cancel at least a portion of the first non-linear current therein, thereby reducing harmonic distortion due to the first non-linear collector-to-substrate capacitance.
1 Assignment
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Accused Products
Abstract
Circuitry for reducing harmonic distortion in an amplifier includes a first transistor having a first non-linear collector-to-substrate capacitance, a first load device coupled to a collector of the first transistor, a first current source coupled to an emitter of the first transistor, a first conductor conducting an input voltage coupled to a base of the first transistor, and a second conductor coupled to the first load device and conducting an output voltage of the amplifier. The first transistor produces a first non-linear current in the first non-linear collector-to-substrate capacitance in response to the input voltage. A second transistor has a second non-linear collector-to-substrate capacitance. A second current source is coupled to an emitter of the second transistor. The first conductor is coupled to apply the input voltage to a base of the second transistor. The second transistor produces a second non-linear current in the second non-linear collector-to-substrate capacitance in response to the input voltage. A current mirror receives a collector current of the second transistor. The current mirror produces in the second conductor a correction signal substantially equal and opposite to the first non-linear current.
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Citations
15 Claims
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1. A method for reducing harmonic distortion in an amplifier including a first transistor having a first non-linear collector-to-substrate capacitance, the method comprising the steps of:
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(a) applying a small signal input voltage to a first conductor coupled to a base of the first transistor and to the base of a second transistor, the second transistor having a second non-linear collector-to-substrate capacitance; (b) producing a first variation in a collector voltage of the first transistor and a second variation in a collector voltage of the second transistor in response to the input voltage, and producing a first non-linear current in the first non-linear collector-to-substrate capacitance in response to the first variation and a second non-linear current in the second non-linear collector-to-substrate capacitance in response to the second variation; (c) causing the first non-linear current to flow in a second conductor connected to the collector of the first transistor; (d) causing the second non-linear current to flow in a control conductor of a current mirror, and operating the current mirror to produce a correction current in an output conductor of the current mirror in response to the second non-linear current; (e) causing the correction current to also flow in the second conductor and thereby cancel at least a portion of the first non-linear current therein, thereby reducing harmonic distortion due to the first non-linear collector-to-substrate capacitance. - View Dependent Claims (2, 3, 4, 5)
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6. Circuitry for reducing harmonic distortion in an amplifier including a first transistor having a first non-linear collector-to-substrate capacitance, a first load device coupled to a collector of the first transistor, a first current source coupled to an emitter of the first transistor, a first conductor conducting an input voltage coupled to a base of the first transistor, and a second conductor coupled to the first load device and conducting an output voltage of the amplifier, the first transistor producing a first non-linear current in the first non-linear collector-to-substrate capacitance in response to the input voltage, the circuitry comprising in combination:
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(a) a second transistor having a second non-linear collector-to-substrate capacitance, a second current source coupled to an emitter of the second transistor, the first conductor being coupled to apply the input voltage to a base of the second transistor; (b) a current mirror having a current control conductor and a current output conductor, the current control conductor being coupled to receive a collector current of the second transistor, and the current output conductor being coupled to the second conductor, the second transistor producing a second non-linear current in the second non-linear collector-to-substrate capacitance in response to the input voltage, the current mirror producing in the second conductor a correction signal substantially equal and opposite to the first non-linear current, in response to the second non-linear current, thereby substantially reducing harmonic distortion produced by the first non-linear collector-to-substrate capacitance. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. A method for reducing effects of a first parasitic capacitance of a first transistor in an amplifier, the method comprising the steps of:
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(a) applying a small signal input voltage to a first conductor coupled to a control electrode of the first transistor and to a control electrode of a second transistor, the second transistor having a second parasitic capacitance; (b) producing a first variation in a current-carrying electrode voltage of the first transistor and a second variation in a current-carrying electrode voltage of the second transistor in response to the input voltage, and producing a first parasitic current in the first parasitic capacitance in response to the first variation and a second parasitic current in the second parasitic capacitance in response to the second variation; (c) causing the first parasitic current to flow in a second conductor connected to a current-carrying electrode of the first transistor; (d) causing the second parasitic current to flow in a control conductor of a current mirror, and operating the current mirror to produce a correction current in an output conductor of the current mirror in response to the second parasitic current (e) causing the correction current to also flow in the second conductor and thereby cancel at least a portion of the first parasitic current therein, thereby reducing the effects of the first parasitic capacitance.
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15. An instrumentation amplifier having low harmonic distortion, comprising in combination:
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(a) a first amplifier; (b) a second amplifier; (c) a difference amplifier having a first input coupled to an output of the first amplifier and a second input coupled to an output of the second amplifier, wherein each of the first and second amplifiers includes circuitry for reducing harmonic distortion in an amplifier including i. a first transistor having a first non-linear collector-to-substrate capacitance, a first load device coupled to a collector of the first transistor, a first current source coupled to an emitter of the first transistor, a first conductor conducting an input voltage coupled to a base of the first transistor, and a second conductor coupled to the first load device and conducting an output voltage of the amplifier, the first transistor producing a first non-linear current in the first non-linear collector-to-substrate capacitance in response to the input voltage, ii. a second transistor having a second non-linear collector-to-substrate capacitance, a second current source coupled to an emitter of the second transistor, the first conductor being coupled to apply the input voltage to a base of the second transistor; iii. a current mirror having a current control conductor and a current output conductor, the current control conductor being coupled to receive a collector current of the second transistor, and the current output conductor being coupled to the second conductor, the second transistor producing a second non-linear current in the second non-linear collector-to-substrate capacitance in response to the input voltage, the current mirror producing in the second conductor a correction signal substantially equal and opposite to the first non-linear current, in response to the second non-linear current, thereby substantially reducing harmonic distortion produced by the first non-linear collector-to-substrate capacitance.
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Specification