Dual-Path RF Power Amplifier With Switch-Isolated Backoff Mode
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Solution Overview
Problem
Existing power amplifiers in mobile handsets are inefficient in current consumption and suffer from excessive linearity margin, especially at low power levels, due to complex circuitry and trade-offs required for high and low power modes, leading to non-optimal performance and increased power loss.
Innovation Solution
A multi-mode RF power amplifier design with two paths, one for high power and one for low power modes, utilizing an RF switch to isolate paths and optimize impedance matching, reducing power leakage and current consumption by sharing power between paths in high power mode and using a bypass network in low power mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single power amplifier design is used for all power levels, then the linearity specification is met at maximum power level, but power added efficiency drops off rapidly at backoff or low power levels resulting in non-optimal current consumption
Solution Approach 1:
The power amplifier is divided into two separate paths: a high power path with a first power amplifier for maximum power operation, and a low power path with a second power amplifier for backoff operation. Each path is independently optimized for its respective power range, allowing the system to achieve both linearity at high power and efficiency at low power by selecting the appropriate path.
Solution Approach 2:
The system dynamically switches between high power and low power paths based on the required output power level. An RF switch controls the selection between paths, and bias control circuitry adjusts the operating state of each amplifier to match the current power level requirements, enabling optimal efficiency across the full power range.
2Use of energy by moving object
If two different parallel signal paths are utilized for LP and HP modes with switches, then efficiency is improved in low power mode, but the switches are lossy, costly, and complex control is required increasing device complexity
Solution Approach 1:
The two power amplifier paths share common input and output impedance matching networks, bias control circuitry, and RF switch control logic. This merging of shared components reduces overall device complexity and cost while maintaining the efficiency benefits of separate optimized paths for high and low power operation.
3Adaptability or versatility
If switches are used to control power flow between paths, then mode switching is enabled, but power loss and current consumption increase and large physical size is required
Solution Approach 1:
The RF switch is strategically placed at a specific location in the signal path where the RF power level is minimized. This positioning reduces the power loss and current consumption associated with the switch operation, as the switch handles lower power levels rather than the full output power of the amplifier.
Data Source
AI summary
A multi-mode RF amplifier is disclosed having high and low output power modes and two power paths. A first RF amplifier delivers power to both paths. When the multi-mode RF amplifier is biased into the high power, HP, mode, substantial power is delivered via both (first and second) paths. While in the low power, LP, mode, an RF switch is turned off, creating a high input impedance, open circuit for the first path, and effectively isolating the two paths. Therefore, power is delivered by the first RF amplifier to the second path only. The impedance presented to the output of the first RF amplifier is equal to the input impedance of the second path which may be optimally set for maximizing power added efficiency or output power in LP mode. Note that, in a preferred embodiment, even in the HP mode more power is delivered to the second power path than to the first power path.