Stacked Power Amplifier Circuit With Impedance Tuning for Stability
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Solution Overview
Problem
The existing power amplifier circuits for mobile communication devices face stability issues due to parasitic capacitance, leading to potential oscillation and reduced stability of the upper-stage transistor, which affects the maximum output power.
Innovation Solution
A power amplifier circuit design that includes an adjustment circuit with a series connection of a capacitor and resistance elements between the upper-stage transistor and ground, which adjusts the impedance seen from the transistor's third terminal, thereby improving stability and preventing oscillation by canceling negative resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two vertically connected transistors are used to double the voltage amplitude and increase maximum output power, then the power amplifier circuit provides larger maximum output power, but the upper-stage transistor becomes less stable and may oscillate due to parasitic capacitance effects
Solution Approach 1:
An adjustment circuit is introduced as an intermediary between the upper-stage transistor and ground. This circuit includes a capacitor connected to the third terminal (base) of the upper-stage transistor and a resistance element connected between the capacitor and ground. The adjustment circuit mediates the interaction between the transistor and ground, adjusting the impedance to prevent oscillation while maintaining the voltage doubling effect.
Solution Approach 2:
The adjustment circuit changes the impedance parameter seen from the third terminal of the upper-stage transistor. By modifying the impedance through the capacitor and resistance element combination, the circuit optimizes the operating conditions to prevent oscillation caused by parasitic capacitance while maintaining the desired voltage amplitude doubling effect.
2Power
If the upper-stage transistor is connected directly to ground via an inductor to enable AC conduction, then the transistor configuration achieves voltage doubling, but parasitic capacitance causes instability and potential oscillation
Solution Approach 1:
The adjustment circuit serves as an intermediary element that modifies the ground connection path for the upper-stage transistor. The capacitor and resistance element combination acts as a mediator that adjusts the impedance characteristics, preventing direct problematic interactions between the transistor's parasitic capacitance and the ground connection.
Solution Approach 2:
The adjustment circuit converts the harmful effect of parasitic capacitance into a beneficial outcome. By introducing the capacitor and resistance element, the circuit transforms the oscillation-prone configuration into a stable one, where the parasitic capacitance is compensated for rather than causing instability.
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 design achieves increased maximum output power while enhancing the stability of the power amplifier circuit, effectively addressing the stability issues caused by parasitic capacitance.
Implementation Method 1
an adjustment circuit that adjusts impedance seen from the third terminal of the upper-stage transistor. The adjustment circuit includes a second capacitor and at least one resistance element, which are connected in series with the ground path between the third terminal of the upper-stage transistor and ground
Implementation Method 2
an inductor that connects the second terminal of the upper-stage transistor to ground
Implementation Method 3
the second terminal is connected to the first terminal of the lower-stage transistor via the first capacitor
Data Source
AI summary
A power amplifier circuit includes a lower-stage transistor having a first power supply voltage supplied to a first terminal, a second terminal connected to ground, and a first signal supplied to a third terminal; an upper-stage transistor having a second power supply voltage supplied to a first terminal, a second signal obtained by amplifying the first signal being output from the first terminal, a second terminal connected to the first terminal of the lower-stage transistor via a first capacitor, and a third terminal connected to ground via a ground path; an inductor that connects the second terminal of the upper-stage transistor to ground; and an adjustment circuit that adjusts impedance seen from the third terminal of the upper-stage transistor. The adjustment circuit includes a second capacitor and at least one resistance element connected in series with the ground path between the third terminal of the upper-stage transistor and ground.