Power Amplifier Bypass Circuit for Low-Distortion Attenuation
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Solution Overview
Problem
Existing power amplifiers face challenges in reducing impedance mismatch between stages, minimizing minimum operating voltage, and suppressing distortion when large power is inputted in the attenuation mode, particularly due to the limitations of GaAs-HBT power amplifiers used in mobile phones and wireless LAN applications.
Innovation Solution
A power amplifier design incorporating a matching attenuation circuit with BC diodes and a current mirror circuit to reduce impedance mismatch and independently design the power amplifier and bypass circuit, while a serial resonant circuit and switch are used to manage the amplification and attenuation modes, reducing distortion by controlling the BC diodes' operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bypass circuit is provided in the amplification stage to realize step attenuation function, then the attenuation function is achieved, but impedance mismatch between stages increases and distortion characteristics degrade when large power is inputted
Solution Approach 1:
The patent divides the bypass circuit into two independent functional parts: an impedance matching circuit (with inductor L and capacitor C) and an attenuation circuit (with resistor Rf and capacitor Cf). This segmentation allows each part to perform its specific function optimally - the matching circuit maintains impedance continuity between stages while the attenuation circuit provides signal attenuation, thereby resolving the contradiction between achieving attenuation and maintaining low distortion.
Solution Approach 2:
The patent introduces an intermediate impedance matching circuit between the power amplifier stage and the attenuation circuit. This intermediary matching circuit acts as a buffer that maintains proper impedance matching between stages even when the attenuation circuit is active, preventing the impedance mismatch that would otherwise cause signal reflections and distortion.
2Device complexity
If BC diodes are used to compose RF switch elements, then single power source operation is enabled, but impedance mismatch between input and output increases in attenuation mode
Solution Approach 1:
The patent introduces an intermediate impedance matching circuit (with inductor L and capacitor C) between the BC diode-based attenuator and the power amplifier stage. This intermediary matching network compensates for the impedance transformation effect of the BC diodes, maintaining proper 50-ohm impedance matching between input and output even when the attenuator is in the attenuation state, thus resolving the impedance mismatch problem.
3Use of energy by moving object
If the power amplifier stage is turned off for attenuation, then current consumption is reduced, but distortion characteristics degrade when large power is inputted due to self-bias effect
Solution Approach 1:
The patent segments the signal path into an amplification stage and an attenuation stage that can operate independently. When attenuation is needed, the power amplifier can be turned off (saving current) while the attenuation circuit remains active and properly impedance-matched through the matching circuit, preventing the self-bias distortion that would occur if the amplifier stage alone handled the attenuation.
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 solution effectively lowers the minimum operating voltage, reduces impedance mismatch, and suppresses distortion characteristics during high-power input in the attenuation mode, enabling more flexible design and improved performance.
Implementation Method 1
a serial resonant circuit connected between the base of said amplifying transistor and a grounding point, whose resonance frequency is set in the operating frequency band of said amplifying transistor
Implementation Method 2
a switch using a base-collector junction diode (BC diode) having a junction close to a p-i-n junction is used
Data Source
AI summary
A power amplifier includes: an amplifying transistor; a bias circuit; a first diode; a second diode; a matching attenuating circuit; a first current mirror circuit; a serial resonant circuit, and a switch. In an amplification mode, the bias circuit supplies a bias current to the amplifying transistor, and the first current mirror circuit turns off the first and second diodes, and the switch. In an attenuation mode, the bias circuit supplies no bias current to the amplifying transistor, and the first current mirror circuit turns on the first and second diodes and the switch.