PA Compression Control Circuit for Dynamic Supply Voltage Tracking
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Solution Overview
Problem
Conventional RF power amplifier (PA) systems face inefficiencies due to fixed biasing during off-peak amplitudes of RF signals, leading to wasted power and increased spectral occupancy, and struggle with amplitude-to-phase modulation (AM-to-PM) distortion, especially in high-bandwidth applications, where existing efficiency enhancement techniques like Envelope Elimination and Restoration (EER) fail to provide significant gains.
Innovation Solution
A power amplifier controller circuit with closed amplitude and phase control loops that adjusts the supply voltage and phase of the RF signal based on amplitude and phase error signals, using a combination of switched mode power supplies and variable gain amplifiers to optimize efficiency and reduce AM-to-PM distortion, while avoiding the use of SAW filters in the correction loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the output transistor is biased to remain linear at peak power transmitted, then spectral occupancy is reduced, but power is wasted during off-peak amplitude periods
Solution Approach 1:
The patent implements dynamic biasing of the output transistor by adjusting the supply voltage according to the instantaneous amplitude of the RF input signal. The bias control circuit modifies the operating point of the transistor in real-time, transitioning from fixed biasing to dynamic biasing that adapts to signal conditions, thereby resolving the contradiction between maintaining linearity and reducing power waste.
Solution Approach 2:
The patent changes the supply voltage parameter of the power amplifier based on the amplitude of the input signal. By varying the supply voltage dynamically, the system maintains optimal efficiency across different operating conditions while preventing spectral regrowth, thus addressing both spectral occupancy and power efficiency concerns.
2Loss of energy
If the supply voltage is varied to accommodate large variations in amplitude signal, then efficiency gains are achieved, but the voltage converter becomes complex and difficult to implement
Solution Approach 1:
The patent segments the voltage conversion function into discrete control stages. The bias control circuit divides the amplitude signal processing into detection, comparison, and control stages, implementing voltage adjustment in manageable steps rather than requiring a single complex wide-range voltage converter.
Solution Approach 2:
The patent introduces a bias control circuit as an intermediary between the amplitude signal and the power amplifier. This intermediary circuit simplifies the overall system by handling the voltage conversion and control functions in a dedicated module, reducing the complexity burden on the main voltage converter while achieving the desired efficiency gains.
3Reliability
If fixed biasing is used during off-peak amplitude, then linearity is maintained, but power consumption increases
Solution Approach 1:
The patent transitions from static fixed biasing to dynamic biasing where the bias voltage is continuously adjusted according to the instantaneous signal amplitude. This dynamic approach maintains linearity when needed while reducing power consumption during off-peak periods, directly addressing the contradiction between reliability and energy usage.
Solution Approach 2:
The patent changes the bias voltage parameter dynamically based on signal conditions. By adjusting this key parameter in response to amplitude variations, the system maintains the necessary linearity for reliable operation while optimizing power consumption, resolving the trade-off between these two requirements.
Data Source
AI summary
A power amplifier controller circuit controls a power amplifier based upon an amplitude correction signal indicating the amplitude difference between the amplitude of the input signal and an attenuated amplitude of the output signal. The power amplifier controller circuit comprises an amplitude control loop and a phase control loop. The amplitude control loop adjusts the supply voltage to the power amplifier based upon the amplitude correction signal.The amplitude loop may include a variable gain amplifier adjusting the amplitude of the input signal. The amplitude loop can include a compression control block which may be configured either to adjust the gain in the variable gain amplifier or the voltage from the power supply based upon the operating level of the other, in addition to being based upon the amplitude correction signal, thus providing a way of maintaining the depth beyond the PA's compression point and allowing a control of the efficiency of the RF power amplifier.