Predistorter Circuit With Variable Capacitance for Amplifier Linearity
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Solution Overview
Problem
Amplifiers in communication systems face challenges in compensating for linearity issues, particularly amplitude and phase distortions, which affect communication distance, quality, and standby time, due to the complexity of compensating for the interrelated nature of these distortions.
Innovation Solution
A predistorter is used, comprising a capacitor and an impedance conversion circuit with a bipolar junction transistor or field-effect transistor, to provide variable capacitance and adjust linearity by isolating direct-current signals and performing impedance conversion, thereby compensating for amplitude and phase distortions without significantly altering the amplifier's original design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional amplifiers are used to amplify signals, then communication distance and power can be extended, but amplitude distortion and phase distortion increase, degrading linearity and communication quality
Solution Approach 1:
The predistorter applies preliminary distortion compensation to the input signal before it enters the amplifier. By pre-distorting the signal in the opposite direction of the amplifier's expected distortion, the overall system achieves linear output despite the amplifier's nonlinear characteristics. This preliminary action prevents distortion rather than correcting it after the fact.
Solution Approach 2:
The predistorter acts as an intermediary device between the signal source and the amplifier. It processes the signal to anticipate and counteract the amplifier's nonlinear behavior, serving as a mediator that prepares the signal for the amplifier's specific distortion characteristics, thereby improving overall system linearity.
2Manufacturing precision
If complex predistortion circuits are used to compensate for both amplitude and phase distortion, then linearity improves, but device complexity and volume increase
Solution Approach 1:
The patent combines amplitude distortion compensation and phase distortion compensation into a single integrated predistorter circuit. By merging these functions and utilizing the amplifier's existing output signal to control the predistortion process, the design achieves comprehensive distortion compensation without requiring separate complex circuits for each function, thereby reducing overall device complexity and volume.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The predistorter effectively compensates for amplitude and phase distortions, reducing issues such as large volume, low gain, and narrow bandwidth in amplifiers, while allowing for fine-tuned linearity adjustments to meet various design requirements.
Implementation Method 1
The predistorter comprises a first capacitor, a first bias input circuit and an impedance conversion circuit. The first capacitor has a first end coupled to a first node of the amplifier. The impedance conversion circuit is configured to perform an impedance conversion to provide a variable capacitance.
Implementation Method 2
The impedance conversion circuit is configured to perform an impedance conversion to provide a variable capacitance. The impedance conversion circuit comprises a bipolar junction transistor (BJT).
Implementation Method 3
The impedance conversion circuit is configured to perform an impedance conversion to provide a variable capacitance. The impedance conversion circuit comprises a bipolar junction transistor (BJT). The BJT has a base coupled to an output end of the first bias input circuit and a second end of the first capacitor, a floating collector, and an emitter coupled to a second node of the amplifier.
Implementation Method 4
The impedance conversion circuit is configured to perform an impedance conversion to provide a variable capacitance. The impedance conversion circuit comprises a first resistor and a field-effect transistor (FET). A gate of the FET is coupled to an output end of the first bias input circuit, one of a source and a drain of the FET is coupled to a second end of the first capacitor and a first end of the first resistor, another of the source and the drain of the FET is coupled to an output end of the second bias input circuit, a first end of the second capacitor and a second end of the first resistor, and a second end of the second capacitor is coupled to a second node of the amplifier.
Implementation Method 5
The impedance conversion circuit is configured to perform an impedance conversion to provide a variable capacitance. The impedance conversion circuit comprises a first bias input circuit and a diode. The first bias input circuit is configured to receive a first bias. An anode of the diode is coupled to an output end of the first bias input circuit and a second end of the first capacitor, and a cathode of the diode is coupled to a second node of the amplifier.
Data Source
AI summary
A predistorter has a first capacitor, a first bias input circuit, a second bias input circuit, a second capacitor and an impedance conversion circuit. A first end of the first capacitor is coupled to a first node of the amplifier. The impedance conversion circuit has a first resistor and a field-effect transistor (FET) and is used to perform an impedance conversion to provide a variable capacitance. A gate of the FET is coupled to an output end of the first bias input circuit, one of a source and a drain of the FET is coupled to a second end of the first capacitor and a first end of the first resistor, and another of the source and the drain of the FET is coupled to an output end of the second bias input circuit, first end of the second capacitor and a second end of the first resistor.