Amplifier Output Power Correction Under Load Impedance Variation
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Solution Overview
Problem
Conventional power amplifier techniques fail to maintain constant output power under variations in load impedance, leading to significant power fluctuations, especially in transmitter systems using predistortion for complex data modulations like EDGE communications.
Innovation Solution
An output power correction module that adjusts the collector voltage and current of power amplifiers using a feedback loop and correction factor, derived from ideal and measured collector currents, to maintain constant collector efficiency and output power despite load impedance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage or current control techniques are used to indirectly control output power, then compensation for variations in operating conditions (temperature and supply voltage) is achieved, but significant variations in power delivered to varying load occur (up to 10.0 dB)
Solution Approach 1:
The patent implements a feedback loop that directly measures the output power of the power amplifier and uses this measurement to adjust the control voltage. This closed-loop feedback mechanism ensures that the output power remains constant despite variations in load impedance, temperature, or supply voltage, resolving the contradiction between operating condition compensation and power delivery stability.
Solution Approach 2:
The patent dynamically adjusts the control parameters of the power amplifier based on real-time output power measurements and load impedance detection. By continuously adapting the control voltage and current according to actual operating conditions, the system maintains constant output power across varying loads, temperatures, and supply voltages.
2Power
If constant DC power is delivered to power amplifier by utilizing feedback loop to adjust collector voltage, then constant output power is achieved under constant collector efficiency, but significant problems occur in transmitter systems utilizing predistortion
Solution Approach 1:
The patent changes the control parameter from collector voltage alone to a combination of collector voltage and collector current control. By adjusting both parameters based on output power measurements and load impedance detection, the system achieves constant output power while maintaining compatibility with predistortion techniques used in modern communication systems.
Solution Approach 2:
The patent incorporates load impedance detection and correction factor calculation in advance of the power amplification process. By determining the appropriate correction factors based on detected load conditions and applying them to the control signals before amplification, the system ensures constant output power while maintaining predistortion functionality.
3Power
If output power is maintained constant under load impedance variations, then power amplifier performance is improved, but complex control mechanisms are required
Solution Approach 1:
The patent implements a control mechanism that simultaneously handles multiple functions: output power measurement, load impedance detection, correction factor calculation, and control signal adjustment. This multi-functional approach achieves constant output power under varying load conditions while avoiding the need for separate complex control circuits for each function.
Data Source
AI summary
According to an exemplary embodiment, a transmitter system includes a power amplifier receiving a supply voltage and a supply current from a power control/current detection circuit, where the power amplifier drives a load impedance. The transmitter system further includes a power correction module configured to sample the supply current and to cause a change in a control voltage, which corrects the supply voltage in response to a change in the load impedance. The supply voltage is corrected to cause the power amplifier to have a substantially constant output power. The power correction module is further configured to output a corrected peak voltage determined by an average value of the supply current. The transmitter system further includes a predistortion module configured to determine the control voltage from a product of the corrected peak voltage and an amplitude modulation component and to output the control voltage to the power control/current detection circuit.