High-Frequency Amplifier Output Matching for Switched Power Levels
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Solution Overview
Problem
Conventional high frequency amplifiers face issues with optimized output load impedance, leading to deteriorated characteristics, increased loss, and oscillations due to insufficient isolation when switching between high and low output power levels, particularly because the impedance of the turned-off amplifier affects the output matching circuit and the high frequency signal can pass around the turned-off amplifier.
Innovation Solution
A high frequency amplifier design featuring two amplifying elements of different sizes connected in parallel, with separate bias control circuits and output matching circuits that include high pass and low pass filter type matching circuits, ensuring the impedance is matched to 50 ohms regardless of the output power level, thereby preventing signal leakage and enhancing isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If two amplifiers of different sizes are connected in parallel and switched according to output level, then efficiency in low output power is improved, but output load impedance is not optimized and characteristics are deteriorated when amplifier is switched
Solution Approach 1:
The output matching circuit is segmented into two separate matching circuits, one for each amplifier size. Each matching circuit is independently optimized for its corresponding amplifier, allowing proper impedance matching in both high and low power modes without compromising characteristics during switching.
Solution Approach 2:
The output matching circuit is dynamically switched between two configurations based on the operating mode. A switch selectively connects either the first matching circuit (for large amplifier, high power) or the second matching circuit (for small amplifier, low power), ensuring optimal impedance matching across all operating conditions.
2Device complexity
If the same matching circuit is used for both amplifiers, then device complexity is reduced, but output load impedance is not optimized and characteristics are deteriorated
Solution Approach 1:
The matching circuit is divided into two separate circuits instead of using one unified circuit. This segmentation allows each circuit to be specifically designed and optimized for its corresponding amplifier size, resolving the contradiction between simplicity and performance.
Solution Approach 2:
The switching mechanism provides multi-functionality by selectively connecting different matching circuits based on operating conditions. The switch itself becomes a universal component that adapts the system to different configurations, managing complexity while enabling optimized performance.
3Device complexity
If the impedance of the turned-off amplifier is low, then circuit simplicity is maintained, but loss in the output matching circuit increases and characteristics are deteriorated
Solution Approach 1:
The harmful impedance effect of the turned-off amplifier is extracted and isolated from the active signal path. By using a separate matching circuit for the turned-off amplifier and properly switching it out, its low impedance no longer loads down the active circuit, eliminating the loss mechanism while maintaining circuit simplicity.
4Device complexity
If isolation of the turned-off amplifier is insufficient, then device complexity is reduced, but high frequency signal passes around and causes oscillation
Solution Approach 1:
The switch acts as an intermediary component between the amplifiers and the output matching circuit. It provides high-frequency isolation by completely disconnecting the turned-off amplifier from the signal path, preventing oscillation while adding minimal complexity to the overall system.
Data Source
AI summary
Provided is a high frequency amplifier including two amplifying elements of different element sizes connected in parallel and switching the amplifying elements in accordance with a level of output power. In particular, the high frequency amplifier includes an output matching circuit for matching to characteristic impedance (50 ohms) both when the output power is high and low, and increasing impedance when the turned-off amplifying element is viewed from a connection node on an output side of the two amplifying elements. Consequently, characteristics such as high output power and high efficiency can be achieved and it is possible to prevent an amplified high frequency signal from passing around to a matching circuit on a turned-off amplifying element side.