Gate Bias Resistor Matching for Low-Distortion Power Amplifiers
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Solution Overview
Problem
Existing power amplifier designs for third-generation mobile communication systems, such as WCDMA and cdma2000, face challenges in improving distortion characteristics, particularly in linear amplifiers, as current gate bias circuits do not adequately address distortion issues and rely heavily on impedance matching circuit adjustments which are insufficient.
Innovation Solution
A semiconductor integrated circuit device with a high-frequency power amplifier that includes a transistor with a gate bias circuit featuring a gate resistor and inductance series-connected between the bias power supply voltage and the transistor gate, where the gate resistor has a resistance value matching the transistor's input impedance, including a feedback capacitance, to optimize the distortion characteristic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a high resistance value gate resistor (10 kΩ or so) is used in the gate bias circuit to avoid leakage of high-frequency signal, then high-frequency signal leakage is reduced, but distortion characteristic improvement is not achieved
Solution Approach 1:
The patent changes the resistance value parameter of the gate resistor from the conventional high value (10 kΩ) to a low value (10 Ω or less), which fundamentally alters the circuit's frequency response and impedance characteristics. This parameter change enables the gate resistor to provide distortion compensation by creating a specific voltage division effect that counteracts nonlinear distortion in the power amplifier stage.
Solution Approach 2:
The gate resistor serves as an intermediary element that mediates between the bias voltage source and the transistor gate. By positioning this low-value resistor in the signal path, it creates a controlled voltage drop that acts as a distortion compensation mechanism, indirectly improving linearity without requiring complex additional circuits.
2Productivity
If impedance matching circuits are adjusted to optimize input-output characteristics, then power transfer is optimized, but distortion characteristic improvement is insufficient
Solution Approach 1:
The patent merges the distortion compensation function with the existing gate bias circuit by incorporating a low-value resistor into the bias network. This combines multiple functions (biasing, impedance matching, and distortion compensation) into a single integrated circuit configuration, eliminating the need for separate distortion correction circuits.
Solution Approach 2:
The gate resistor in this configuration serves multiple functions simultaneously: it provides DC biasing, establishes AC ground reference, optimizes input impedance matching, and compensates for nonlinear distortion. This multi-functionality resolves the contradiction by achieving both power transfer optimization and distortion reduction through a single circuit element.
Data Source
AI summary
The present invention is to provide a technique which optimizes a gate resistor of a bias circuit to thereby make it possible to greatly improve a distortion characteristic of a power amplifier. A bias circuit used as for biasing the gate of a final-stage power transistor is included in a power amplifier provided in a communication mobile system. In the bias circuit, an inductance and a resistor are series-connected between a power supply voltage and the gate of the power transistor. The resistance value of the resistor is set to approximately the same order as an input impedance of the power transistor. When the input impedance of the power transistor is about 10Ω or so, for example, the resistor is set to about a few Ω to about 100Ω. Thus, the gain of the power transistor at a low-frequency band can greatly be suppressed.