Amplifier Output Power Correction for Load Impedance Changes
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Solution Overview
Problem
Conventional power amplifier systems fail to maintain constant output power under variations in load impedance, particularly in transmitter systems using predistortion for complex data modulations like EDGE, leading to significant power fluctuations.
Innovation Solution
An output power correction system that adjusts the average peak voltage of the power amplifier by calculating a correction factor based on the measured collector current, ensuring constant collector efficiency and thus maintaining constant 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 adequate, but significant variations in power delivered to varying load occur (up to 10.0 dB)
Solution Approach 1:
The patent implements a feedback mechanism that directly measures the output power of the power amplifier and uses this measurement to adjust the control voltage. The feedback loop compares the actual output power with the desired output power and generates a correction signal to minimize the difference, thereby maintaining constant power delivery despite load impedance variations.
Solution Approach 2:
The patent changes the control parameter from indirect voltage/current control to direct output power control. By measuring the actual output power and using this parameter to adjust the amplifier's operating point, the system achieves both adequate compensation for operating conditions and stable power delivery to varying loads.
2Power
If constant DC power is delivered to power amplifier by utilizing feedback loop to adjust collector voltage, then constant output power can be provided if constant collector efficiency is maintained, but significant problems occur in transmitter systems utilizing predistortion
Solution Approach 1:
The patent changes the control approach from maintaining constant collector efficiency to directly controlling output power measurement. This parameter change allows the system to work effectively with predistortion techniques by focusing on the actual output power rather than intermediate efficiency parameters, thereby achieving both constant power output and compatibility with predistortion transmitter systems.
3Device complexity
If conventional power control techniques are used, then simple control architecture is maintained, but output power varies significantly (up to 10.0 dB) under load impedance changes
Solution Approach 1:
The patent introduces a direct output power feedback loop that measures the actual power delivered to the load and uses this information to adjust the amplifier's operating point. This feedback mechanism significantly improves output power stability under varying load conditions while adding minimal complexity to the overall control architecture.
Data Source
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AI summary
An embodiment of a transmitter system (200) includes a power amplifier (206) receiving a supply voltage (254) and a supply current (234) from a power control/current detection circuit (208). The transmitter system further includes a power correction module (224) configured to sample the supply current and to cause a change in a control voltage (242), 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 (232) determined by an average value of the supply current. The transmitter system further includes a predistortion module (216) configured to determine the control voltage from a product of the corrected peak voltage and an amplitude modulation component (238) and to output the control voltage to the power control/current detection circuit.